The Pathogenesis of Polycystic Ovary Syndrome (PCOS): The Hypothesis of PCOS as Functional Ovarian Hyperandrogenism Revisited

A. Biochemical and molecular overview of steroidogenesis

The rate-determining step for the formation of all steroid hormones in response to tropic hormones in both the gonads and adrenal glands is cholesterol side-chain cleavage, which is mediated by the enzyme cytochrome P450scc (encoded by CYP11A) (62). The ovarian steroidogenic response to LH is slow in the early follicular phase, and is accelerated in the luteinized preovulatory follicle as LH induces the steroidogenic acute regulatory protein, which delivers cholesterol into mitochondria (63).

Cytochrome P450c17 (CYP17A1) is the rate-limiting enzyme for the formation of androgens in the gonads and adrenal cortex (Figure 1) (22, 64). Its expression is absolutely dependent upon tropic hormone stimulation, LH in the ovary (65, 66) and ACTH in the adrenal cortex (67, 68), in a dose-dependent manner. This one enzyme possesses both 17-hydroxylase and 17,20-lyase activities. The first of these activities, 17-hydroxylase, is necessary for the formation of cortisol in the adrenal cortex and the potent sex steroids in the gonads. The second of these activities, 17,20-lyase, less efficiently acts sequentially on enzyme-bound 17-hydroxylated substrate to form 17-ketosteroids, eg, dehydroepiandrosterone (DHEA) or androstenedione. These 17-ketosteroids are, in turn, the precursors of all potent sex steroids in the gonads and adrenal zona reticularis. Specifically, P450c17 mediates conversion of pregnenolone by 17-hydroxylation to form 17-hydroxypregnenolone, which is transformed by 17,20-lyase activity to DHEA. DHEA is then converted by Δ5-isomerase-3β-hydroxysteroid dehydrogenase type 2 (3βHSD2) (HSD3B2) to androstenedione. Progesterone undergoes parallel P450c17 17-hydroxylation to 17OHP. Although 17OHP is a poor substrate for P450c17 17,20-lyase activity in theca cells or cell-free systems, formation of androstenedione has been documented in ovarian and adrenal homogenates and minces (69,–71), compatible with the possibility that either paracrine interactions with granulosa cells may up-regulate 17,20-lyase activity for this substrate or that another enzyme accounts for this activity (22).

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Figure 1.

Depiction of the organization and regulation of the major steroid biosynthetic pathways in the small antral follicle of the ovary according to the 2-gonadotropin, 2-cell model of ovarian steroidogenesis. LH stimulates androgen formation within theca cells via the steroidogenic pathway common to the gonads and adrenal glands. FSH regulates estradiol biosynthesis from androgen by granulosa cells. Long-loop negative feedback of estradiol on gonadotropin secretion does not readily suppress LH at physiologic levels of estradiol and stimulates LH under certain circumstances. Androgen formation in response to LH appears to be modulated by intraovarian feedback at the levels of 17-hydroxylase and 17,20-lyase, both of which are activities of cytochrome P450c17 that is expressed only in theca cells. The relative quantity of androstenedione formation via 17OHP (dotted arrow) in the intact follicle is probably small, as is the amount of progesterone formed from granulosa cell P450scc activity in response to FSH (data not shown). 17βHSD2 activity is minor in the ovary, and estradiol is primarily formed from androstenedione. Androgens and estradiol inhibit (minus signs) and inhibin, insulin, and IGF-1 (IGF) stimulate (plus signs) 17-hydroxylase and 17,20-lyase activities. Pertinent enzyme activities are italicized: the 17-hydroxylase and 17,20-lyase activities of P450c17 are shown, otherwise enzyme abbreviations are as in the text. Modified with permission from Ehrmann et al, Polycystic ovary syndrome as a form of functional ovarian hyperandrogenism due to dysregulation of androgen secretion. Endocr Rev. 1995;16:322–353 (22).

The differential regulation of the 2 enzyme activities of P450c17 is incompletely understood. The preferential formation of androgen by P450c17 of the gonads and adrenal zona reticularis is largely dependent on 3 posttranslational factors that up-regulate its 17,20-lyase activity (64). First, this activity is especially sensitive to the molar abundance of the electron-transfer protein cytochrome P450-oxidoreductase (POR). Second, cytochrome b5 (CYB5A) strongly promotes 17,20-lyase activity, principally by acting as an allosteric factor promoting the interaction of P450c17 with POR. Third, the serine/threonine phosphorylation of P450c17 itself by a specific MAPK (p38α) appears to selectively promote 17,20-lyase activity by also promoting the interaction of P450c17 with POR.

Androstenedione is the major precursor for both testosterone and estrogen synthesis in the ovaries (Figure 1) and adrenal cortex (Figure 2) (62). In the ovaries it is in part converted in theca cells by 17βHSD5 (HSD17B5; also termed α-ketoreductase type 1C3 [AKR1C3]) to form testosterone (72) and is in part aromatized in granulosa cells by cytochrome P450aro (CYP19A1) to form estrone. Androstenedione predominates over testosterone as the aromatase substrate, because it is available in 10-fold greater amounts (60, 62, 72,–75). Estrone is then converted to estradiol by 17βHSD1 (HSD17B1).

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Figure 2.

Depiction of the organization of the major steroid biosynthetic pathways in the adrenal cortex. The top row shows the pathway to aldosterone; the middle row shows the zona fasciculata pathway to cortisol; the lowest, darkly shaded row shows the zona reticularis steps to 17-ketosteroids that are not expressed in the other adrenal zones. Note similarities between the biosynthetic capacities of the zona reticularis and that of ovarian theca cells. Dotted pathways are minor. The zona reticularis is notable for its low 3βHSD2 activity (denoted by small arrow) and unique expression of cytochrome b5, a cofactor which enhances the 17,20-lyase activity of P450c17. Sulfotransferase 2A1 is uniquely expressed in the zona reticularis and rapidly converts DHEA to DHEAS. Compound S (Cpd S), 11-deoxycortisol. Corticosterone and 18-hydroxycorticosterone, the successive intermediates between deoxycorticosterone (DOC) and aldosterone, are not shown. The steroidogenic enzymes are italicized. The clinically relevant electron transfer enzymes also shown are POR and type 1 3′-phosphoadensosine-5′-phosphosulfate synthase (PAPSS). Formation of androstenedione from 17OHP and Cpd S does not seem attributable to CYP450c17. Modified with permission from Rosenfield, Identifying children at risk of polycystic ovary syndrome. J Clin Endocrinol Metab. 2007;92:787–796 (431).

Androgens are preferentially metabolized to dihydrotestosterone rather than estradiol in small ovarian follicles, before follicle selection, because of high steroid 5α-reductase (5αRD) (SRD5A) activity (76). This is carried out by both type 1 and 2 5αRD isozymes in theca, stroma, and granulosa cells, but the predominant reaction is type 1 activity in granulosa cells (77). 17βHSD2 reconversion of testosterone to androstenedione and reconversion of estradiol to estrone are minor pathways.

B. Regulation of ovarian function

Androgens are not only obligate intermediates in the biosynthesis of estradiol. They also have complex effects on follicular growth (78), including up-regulation of aromatase activity (79). It is crucial for the function of the ovary that ovarian androgen secretion be coordinated with the formation of estrogen so that both are optimized for ovulation. Although these processes are critically dependent on LH and FSH concentrations, a variety of intrafollicular modulators are essential to the coordinated function of the ovarian follicle.

2. Regulation of ovarian steroidogenesis

In small antral follicles steroidogenesis is organized as shown in Figure 1 (22). Theca cells produce androgens in response to LH, but granulosa cells do not do so because they do not express CYP17A1 (62). Androgens then diffuse from theca cells to granulosa cells, where they are substrates for estrogen formation in response to FSH because granulosa cells differentially express CYP19A1, which encodes aromatase (62).

a. Homologous desensitization to LH.

The expression of thecal steroidogenic enzymes is absolutely dependent upon LH in a dose-response relationship (22). The normal secretory dose-response curve is asymptotic, however, because as LH rises, desensitization of ovarian responses to LH commences (88,–90). Animal models indicate desensitization is in part mediated by down-regulation of LH receptor-binding sites by ligand binding (22, 91), an endocytic process that involves recycling of receptors via membrane raft microdomains or degradation (92,–94), and in part by down-regulation of the 17,20-lyase activity of P450c17 (22). Thus, as LH stimulation approaches maximal, 17OHP secretion rises, yet normally androgen production increases very little. Judging from serum 17OHP and steroidogenic responses to the LH analog human chorionic gonadotropin (hCG) in normal women, desensitization normally has commenced by half-maximal stimulation of the LH receptor (Figure 3) (90, 95), whereas maximal stimulation causes about a 5-fold increase in 17OHP and small (2-fold) increases in sex steroids (96). Serum 17OHP responses assessed at 4-hour intervals in response to interim dose changes of pulsatile LH suggest that elevating the serum LH 2-fold affects steroid output in normal women comparably with half-maximal LH receptor stimulation (97); however, it is dubious whether 4 hours are sufficient to ascertain the effect full effect of LH on steroidogenesis.

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Figure 3.

Response to half-maximal hCG stimulation during overnight dexamethasone suppression of normal and PCOS subjects. After bedtime dexamethasone 0.25 mg/m², 500-IU hCG was administered im at 8 am; a basal blood sample was drawn before hCG, and the peak response to hCG was sampled after a repeat dexamethasone dose 24 hours later. Subjects were healthy volunteers with normal ovarian morphology (V-NOMs), PCOS patients with functionally typical FOH (ie, 17OHP hyperresponsiveness to GnRHag; PCOS-T), and PCOS patients with functionally atypical FOH (ie, normal 17OHP responsiveness to GnRHag; PCOS-A). V-NOM had a small but significant rise in serum 17OHP but not in other steroids. PCOS-T had hyperresponsiveness of all steroids. PCOS-A, a heterogenous group, had elevated basal serum free testosterone, but normal hCG-responses of all steroids. To convert to SI units, multiply 17OHP by 0.0303 (nM), androstenedione (A'dione) by 0.0340 (nM), free testosterone by 3.47 (pM), and estradiol by 3.67 (pM). Regraphed from data of Hirshfeld-Cytron et al, Characterization of functionally typical and atypical types of polycystic ovary syndrome. J Clin Endocrinol Metab. 2009;94:1587–1594 (95).

b. Modulation of LH action.

Modulation of ovarian androgenic responsiveness to LH involves a number of hormones and growth factors acting in paracrine, autocrine, and endocrine fashions, as modeled in Figure 1 (22). Substantial evidence indicates that estrogen inhibits P450c17 activity by a short-loop (paracrine) negative feedback mechanism (98,–100). Intraovarian androgens inhibit thecal P450c17 activity, but the testosterone effect is not reversed by antiandrogen (101), so it is possible that this androgen effect is estrogen mediated. These inhibiting modulators are counterbalanced by growth factors of granulosa cell origin that are under FSH control and by hormones and cytokines extrinsic to the ovary that amplify P450c17 activities (22, 102,–105). Insulin, IGFs, and inhibin are the best recognized of these modulators (Figure 1). Insulin and IGFs up-regulate P450c17 activities (102) and in rat studies have been shown to up-regulate LH receptor sites (16, 91, 106). This counters the normal process of homologous desensitization to LH and thereby potentiates LH-induced androgen synthesis (22, 88). Insulin is approximately equipotent with IGF-1 in this regard, which makes it unlikely that insulin acts through the IGF-1 receptor, because its affinity is about 500-fold less than that for its cognate receptor. More recent studies have indicated that insulin acts through the insulin receptor itself: the effect on human theca cells is specifically neutralized by an antibody to the insulin receptor (105), and selective knockout of theca cell insulin receptors attenuates the androgenic response to hCG in mice (25). Furthermore, the hyperandrogenic anovulation induced by an obesogenic diet in association with 10- to 20-fold elevation of serum insulin in wild-type mice does not occur in transgenic littermates that lack the theca cell insulin receptor (25). Insulin also directly up-regulates 17βHSD5 gene expression and activity, stimulating testosterone formation from androstenedione (107).

Studies in women with PCOS have demonstrated that a previously unrecognized protein variant, differentially expressed in normal and neoplastic development (DENND)1A.V2, is a facilitator of steroidogenesis in androgen-producing cells, as discussed below in the section on etiology of PCOS/genetic traits (see section VI) (108). At this time, its mechanism of action is unclear.

Inhibin-B, a peptide secreted by granulosa cells of small antral follicles in response to FSH, seems essential for androgenic responses to LH and may be modulated by androgens (95, 109). It seems necessary but not sufficient for up-regulation of CYPA1 gene expression (110). Patients with inactivating mutations of FSH lack hyperandrogenism, despite very high levels of LH. Such patients have low inhibin-B levels, and when exogenous FSH is given, inhibin-B rises dramatically, and the response of theca cell steroids to hCG/LH increases markedly (103, 111). Inhibin-B seems to play a permissive role, rather than a stimulatory role, in determining theca cell LH responsiveness because our data indicate that FSH administration normally suppresses testosterone levels, seemingly through the paracrine action of other granulosa cell factors under its control (95).

Numerous other small molecules of granulosa cell and oocyte origin both positively and negatively modulate LH action in theca cells so as to optimize the follicular environment for oocyte maturation (22). These factors include TGF-β superfamily members such as bone morphogenetic proteins (BMPs), other growth and differentiation factors, cytokines such as TNFα, and microRNAs (90, 112,–119).

Catecholaminergic overactivity also amplifies the ovarian steroidogenic response to hCG in rodents, with signaling via β2-adrenoreceptors on thecal cells (120,–123). In a unique rodent model of PCOM induced by a single injection of estradiol valerate, central sympathetic nervous system (SNS) activity is increased resulting in increased adrenomedullary noradrenergic activity, increased ovarian sympathetic nerve stimulation, and increased intraovarian synthesis of nerve growth factor (NGF), a sympathetic neurotrophin secreted by thecal cells. This is followed by the development of PCOM, anovulation, and increased androgen responses to hCG. These changes are reversed by transection of the superior ovarian nerve. Transgenic mouse NGF overexpression causes increased androgen production in response to pregnant mare serum, a higher prevalence of follicular cysts after sustained increases in LH, enhanced sympathetic outflow, increased body fat with disproportionate hyperinsulinemia, and glucose intolerance (121, 123).

In summary, androgen blood levels are not tightly controlled by direct negative feedback by the pituitary trophic hormones, as is the case for estradiol and cortisol. Rather, intraglandular paracrine and autocrine mechanisms seem to play a major role in the regulation of ovarian androgen secretion. Due to the process of homologous desensitization to LH, once serum LH levels approximate high-normal, intraovarian modulation of LH action seems to be the major factor determining ovarian androgen formation. Insulin counters the desensitization process and sensitizes the ovary to LH.

C. Regulation of adrenal androgen production

The zona reticularis of the adrenal gland (Figure 2) resembles the theca cell compartment of the ovary in its expression of the core enzymatic pattern for androgen production. Zona reticularis cells become discernable in the central adrenal cortex at 3 years of age. As it begins to develop into a continuous zone at about 5–6 years of age, it becomes discernable as “adrenarche,” the maturational increase in adrenal androgen production that is indexed by increased DHEA sulfate (DHEAS) production (161).

Adrenarche represents a change in the pattern of the adrenocortical secretory response to ACTH. It is characterized over time by disproportionately increasing responsiveness of Δ⁵-steroid intermediates (17-hydroxypregnenolone and DHEA) compared with Δ⁴-steroids (eg, 17OHP and androstenedione) in the presence of stable responses of cortisol (162, 163).

A unique zona reticularis enzyme expression profile underlies this adrenarcheal pattern of adrenal secretion. Zona reticularis cells express low 3βHSD2, but high CYB5, and steroid sulfotransferase (SULT2A1) activities (Figure 2) (64, 164, 165). The combination of low 3βHSD2 and high CYB5 activity diverts pregnenolone formation from cortisol to DHEA, and the unique expression of SULT2A1 rapidly sulfates DHEA, forming DHEAS, which accounts for the high secretion of DHEAS by the adrenal cortex (166). SULT2A1 thus acts as a “sump” to direct steroidogenesis to this relatively inert terminal product and prevents adrenal DHEA from being converted into biologically active androgens (165). Seladin-1 (24-dehydrocholesterol RD), expressed in both zona fasciculata and reticularis cells, enhances DHEA, but not cortisol, secretion in vitro, which suggests that it enhances 17,20-lyase activity (167). Enhanced expression of HSD17B5 by this zone accounts for the small but significant adrenal contribution to testosterone secretion (168).

Zona reticularis development requires ACTH, but its determinants are otherwise poorly understood. The stimulus has long been thought to be of pituitary origin (169, 170). Adrenarche is not directly related to the pubertal maturation of the neuroendocrine-gonadotropin-gonadal axis. Adiposity is strongly related to adrenarche, and insulin, IGF-1, and leptin have been suggested as determinants of this relationship (171,–177). Adrenarche is severely attenuated in somatotropin- and thyroxine-replaced patients with deficiency of the pituitary-specific transcription factor Pit-1/POU1F: because this gene defect causes a congenital deficiency of somatotropin, thyrotropin, and prolactin, and the former hormones were replaced, a role for prolactin is suggested (178). IL-6 is another candidate because it is strongly expressed in the zona reticularis of the adrenal cortex and stimulates DHEA secretion (179). On the other hand, a BMP4 signaling system has been identified in the zona reticularis that is inhibitory to androgen formation (180). Notably, the theca cell steroidogenesis facilitator protein DENND1A.V2 has been localized to the zona reticularis (see section V.A.1.). Other pathways that potentially modulate adrenal androgen formation have been identified in a human adrenocortical carcinoma cell line (181). We favor the hypothesis that whatever the factor(s) responsible for adrenarche, it affects the growth or differentiation of zona reticularis precursor cells, so that they acquire the enzymatic properties that permit them to respond to ACTH by secreting androgens.

D. Regulation of peripheral androgen production

Peripheral formation of testosterone from androstenedione primarily occurs in liver, skin and fat (107, 182,–184). Skin and fat tissue express 3βHSDB1 and 17βHSD5 activities as well as P450aro activity. Although early direct studies of steroid metabolism did not reveal it (185), recent evidence suggests that adipose tissue excess is an important contributor to androgen as well as estrogen excess (47).

No clear picture has emerged of tissue-specific regulation of androgen production in nonendocrine sites. Adipose tissue has become recognized in recent years as an endocrine organ that is an important site of generation of sex steroids and inflammatory cytokines in obesity (186, 187). The ratio of androgenic 17βHSD to aromatase activity in visceral fat is positively correlated with central adiposity, and experimental aromatase deficiency in animals and humans is associated with visceral adiposity (187), implicating increased local androgen production in central adiposity (reviewed in section V.B.1). Notably, insulin up-regulates adipocyte 17βHSD5 gene expression and activity in sc fat (107). Furthermore, 17βHSD5 expression in sc fat correlates with body mass index (BMI) (184). Insulin, glucocorticoids, and inflammatory cytokines also stimulate aromatase activity in adipocytes or preadipocytes (188, 189).

Hepatic 17βHSD5 gene expression, hence testosterone formation from androstenedione, appears to be down-regulated by insulin in liver (107). On the other hand, 5αRD activity, which promotes androgen action, is up-regulated in hyperandrogenic states by mechanisms that involve both insulin resistance (190) and possibly androgen excess itself (191).

Sex hormone-binding globulin (SHBG) is of hepatic origin; it is an important factor in androgen action and metabolism. The SHBG concentration determines the fraction of serum testosterone and other 17β-hydroxysteroid ligands (eg, estradiol, dihydrotestosterone) that are free or bound to albumin. It is thus a major determinant of ligand egress from serum to androgen target tissues and to liver for clearance from the circulation (192). SHBG levels are raised by estrogen and suppressed by androgen, insulin resistance in obesity, and hypothyroidism (192, 193). Although the low SHBG in obese individuals has long been attributed to hyperinsulinemia (194), recent evidence suggests that monosaccharide excess itself, signaling via inflammatory cytokines, mediates the SHBG response to obesity (193, 195). Rarely, mutations cause very low levels of SHBG (196).

B. FOH in PCOS

PCOS is a diagnosis of exclusion by standard criteria (Table 1). Therefore, it is necessary to consider other causes of hyperandrogenism in the differential diagnosis, although they account for only 10%–20% of adults presenting with hyperandrogenic symptoms (Table 4) (50, 204,–206).

The unique ovarian dysfunction of PCOS (primary FOH) was first demonstrated by GnRHag testing (22). The pattern of steroidogenesis indicated generalized overactivity of the entire ovarian steroidogenic cascade involved in sex steroid secretion. An elevated 17OHP response was the most consistent abnormality in classic PCOS, which suggested a prominent abnormality at the level of P450c17 activities. Subsequent clinical studies have shown that ovarian steroidogenesis in PCOS is typically similarly hyperresponsive to both the endogenous LH and FSH surge elicited by administration of GnRHag challenge or by hCG challenge (90, 96, 199, 207).

FOH is the common denominator in the vast majority of PCOS. However, as reviewed next, FOH is neither always typical nor always demonstrable in PCOS (Table 2).

1. Spectrum of ovarian androgenic function in PCOS: Typical and atypical FOH

Initially, we reported that the first 7 women with classic PCOS who underwent GnRHag testing had 17OHP hyperresponsiveness in comparison with 16 nonhirsute eumenorrheic women in the midfollicular phase of their menstrual cycle (17). Then, we demonstrated that most (58%) hyperandrogenic women (n = 40) had this PCOS type of 17OHP hyperresponsiveness to GnRHag testing conducted post-DAST in comparison with 13 controls (19). Eighty-seven percent of those with abnormal responses to GnRHag were oligomenorrheic. This abnormality in hyperandrogenic women correlated well (r = 0.75; r² = 0.56) with elevated plasma free testosterone in response to the 5-day DAST, with concordance in 85% of women, in contrast to the findings that polycystic ovaries or elevated LH levels occurred in only about half.

Although subsequent reports confirmed the presence of a significant difference in 17OHP responses to GnRHag between PCOS and control women, they differed widely in their estimates of the prevalence of this abnormality, with some reporting its presence in only a distinct minority (208, 209). We believe this low prevalence is due to failure to exclude women with PCOM from the reference control group, for reasons discussed in the following section.

From 2000 to 2007, we sought to determine the prevalence of FOH in hyperandrogenic women with anovulatory symptoms (PCOS), controlling for the presence of PCOM (197). We performed a GnRHag test and a DAST in 99 consecutively consenting PCOS patients who presented to our clinics and who met NIH criteria (elevated serum free testosterone and ovulatory dysfunction) and compared them with nonhirsute eumenorrheic volunteers, the reference group being volunteers with ultrasonographically normal ovarian morphology (V-NOM) (n = 21). Volunteers were studied in the midfollicular phase of their menstrual cycles (d 4–10) so as to match them for follicular status as well as possible with PCOS. The study protocol included assessment for PCOM, AMH levels, and glucose tolerance. We found that 69% of PCOS, defined by NIH criteria, had typical 17OHP hyperresponsiveness to GnRHag (197).

To better understand the differences between those PCOS patients with 17OHP hyperresponses (functionally typical PCOS [PCOS-T]) and those who lacked 17OHP hyperresponsiveness (functionally atypical PCOS [PCOS-A]), we then analyzed age-matched subsets of PCOS-T (n = 40), PCOS-A (n = 20), and nonhirsute eumenorrheic volunteers, the reference group being V-NOM. We determined the sources of androgen in these 2 functional types of PCOS and related the findings to glucose intolerance in 1 report (47), related ovarian androgenic function to markers of folliculogenesis (PCOM and serum AMH) in another (39), and then integrated these findings (30). Approximately half of the study subjects were adolescents (>1.0 y postmenarcheal and 11.0–17.9 y of age); adults were 18.0–39.9 years old. Within the volunteer and PCOS groups, adolescents and adults had similar baseline androgen, 17OHP, and LH levels (30). The data are displayed in Figure 4 (30).

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Figure 4.

Scatterplots demonstrating relationships among tests for ovarian hyperandrogenism, PCOM, and serum AMH concentrations. Subjects are patients with PCOS identified by NIH criteria (n = 20 PCOS-A, n = 40 PCOS-T) and age-matched healthy eumenorrheic nonhirsute volunteers with normal or PCOM (V-NOM n = 21, V-PCOM n = 32, respectively). Serum for AMH was available in 92% of PCOS and 82% of these volunteers (39). PCOM was defined according to modified Rotterdam criteria: in adults, it was defined as an ovary more than 10.5 cc (in adolescents, >10.8 cc) using the formula for a prolate ellipsoid and/or more than or equal to 10 follicles 2–9 mm in diameter in the maximum plane (27, 39). Dotted lines show normal ranges for the V-NOM reference group; thus (a) quadrant panels show normal ranges. A, PCOS-T is defined by an elevated 17OHP response to the GnRHag test (c and d). SDAST results correlate with GnRHag results (r = 0.671, P < .0001). SDAST is abnormal in 92.5% of PCOS-T. PCOS-A is defined by lack of 17OHP hyperresponse to GnRHag. The SDAST divides PCOS-A into those with (b) and without (a) ovarian androgenic dysfunction. SDAST indicates that 60% of these PCOS-A cases have atypical FOH (b) and 40% of PCOS-A cases have normal ovarian androgenic function (a). B, SDAST relationship to baseline AMH levels. C, 22% (n = 7) of asymptomatic V-PCOM have baseline hyperandrogenemia (hyperandrogenic PCOM [V-PCOMh]). These all proved to have FOH, as indicated by an abnormal SDAST or GnRHag test (b–d). Adolescent V-PCOM tended to have this asymptomatic FOH less often (1/9) than adult (6/23) V-PCOM. Dysregulated PCOM (V-PCOMd), defined by an abnormal 17OHP response to GnRHag in the absence of baseline hyperandrogenemia (d), was found in 25% (n = 8) V-PCOM. D, Mild AMH elevation was found in V-PCOM independently of hyperandrogenemia. So as to best illustrate differences among groups, very high values (post-SDAST testosterone up to 107 ng/dL and post-GnRHag l7OHP up to 1380 ng/dL) are plotted off-scale. To convert to SI units, multiply total testosterone by 0.0347 (nM), 17OHP by 0.0303 (nM), and AMH by 7.125 (pM). Reproduced with permission from Rosenfield, The polycystic ovary morphology-polycystic ovary syndrome spectrum. J Pediatr Adolesc Gynecol. 2015;28:412–419 (30). Since publication of these data, accumulated evidence suggests that in adolescents mean ovarian volume more than 12 cc is a more appropriate criterion for PCOM than more than 10.8 cc (50, 51). Doing so alters the constitution of the V-NOM and V-PCOM groups. With this adjustment and the addition of data on 4 contemporaneously studied but previously overlooked healthy volunteers, our current upper limits for V-NOM (n = 31) are: baseline-free testosterone 9.3 pg/mL and AMH 6.3 ng/mL; SDAST total testosterone 26 ng/dL; and postdexamethasone GnRHag 17OHP 152 ng/dL (50).

Among PCOS-T, those with 17OHP hyperresponsiveness (Table 2 and Figure 5), hyperandrogenism was more severe than in PCOS-A, and the great majority (92.5%) also had an abnormal short DAST (SDAST) and PCOM (Figure 4Ac). Serum AMH was increased in 81%, and the increase was significantly greater than that of any other group. Coincidental FAH was present in 28%. Impaired glucose tolerance (IGT) and frank diabetes were present significantly more often than in PCOS-A or controls; in this series, the only diabetic cases were in PCOS-T. In addition, estradiol secretion was hypersensitive to submaximal hCG stimulation (Figure 3) and FSH administration did not result in the normal inhibition of baseline serum testosterone in PCOS-T (95).

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Figure 5.

Relationships among sources of androgen in PCOS. About two-thirds of cases have functionally typical PCOS (PCOS-T) that is due to typical FOH, in which there is hypersensitivity to LH, characterized by hyperresponsiveness of 17OHP to a GnRHag or hCG test. The remaining one-third of PCOS is functionally atypical, lacking 17OHP hyperresponsiveness. This is a heterogeneous group, most of which have atypical FOH, in which ovarian androgen excess is indicated only by a DAST. A small number are due to isolated FAH. About one-quarter of FOH also have FAH. In a minority of cases, the source of androgen cannot be identified as ovarian or adrenal; most of these are associated with obesity. Modified and reproduced with permission from Rosenfield, Polycystic ovary syndrome in adolescents. In: Rose BD, ed. www.uptodate.com. Waltham, MA: UpToDate; 2014.

PCOS-A is a functionally heterogeneous group (Table 2 and Figure 5). Sixty percent had an abnormal DAST (Figure 4Ab), which defines an atypical form of FOH (Table 2, atypical FOH). FAH coexisted with FOH in 30% of this subgroup. PCOM (65%) and AMH elevation (39%) were found significantly less frequently than in PCOS-T. The prevalence of glucose intolerance was significantly less than in PCOS-T and did not differ from that in the control subjects.

The other 40% of PCOS-A had a normal DAST (Figure 4Aa), ie, no evidence of an ovarian source of androgen. They had significantly milder hyperandrogenemia. This “nonovarian PCOS” itself seems functionally heterogeneous (Table 2). ACTH testing showed “isolated FAH” (Table 2) in 15% of PCOS-A; two-thirds of these had an elevated baseline DHEAS level. However, 85% of the nonovarian subgroup (25% of PCOS-A) lacked FAH, so evidence for a glandular source of androgen was lacking. All in this small subgroup were obese, and we have attributed their androgen excess to excessive peripheral testosterone formation by excessive adipose tissue (“PCOS-A of obesity” in Table 2) (47).

We conclude that there is a spectrum of pathophysiologic dysfunction in PCOS that generally corresponds to clinical severity (30): the PCOS-T group, which has an ovarian secretory pattern suggestive of dysregulation of steroidogenesis prominent at the level of the 17-hydroxylase/17,20-lyase activities of P450c17 (Figure 1), constitutes two-thirds of PCOS and is significantly more clinically severe than PCOS-A, although considerable clinical overlap exists. Furthermore, these data suggest heterogeneity in the pathophysiologic basis of FOH. It remains to be proven whether these pathophysiologic categorizations have clinical utility beyond possibly identifying a subpopulation of PCOS patients whose androgen excess arises from simple obesity and so would be expected to be reversible by weight loss (210, 211) or distinguishing adolescents with PCOS from those with physiologic anovulation (53). Biochemical categorization is expected to prove useful in developing phenotype-genotype correlations, as discussed later: only when we understand the etiology of PCOS will it be possible to truly assess the sensitivity and specificity of these tests.

2. Spectrum of ovarian androgenic function in asymptomatic women with PCOM

PCOM is a common finding among healthy women. Many of these women have mild PCOS features, ie, irregular menstrual cycles and/or hirsutism (212, 213). When care has been taken to exclude those with such symptoms, groups of apparently normal women with PCOM, including some with documented ovulatory cycles, have been shown to have subclinical androgenic ovarian dysfunction that is intermediate between that of women with normal ovaries and those with PCOS (31, 207, 214).

AMH serum concentrations in normal subjects with PCOM are also intermediate between those of women with NOM and those with PCOS (215,–217). Data vary as to whether insulin resistance is associated with PCOM in healthy adult volunteers (31, 214, 218).

We have studied the ovarian androgenic function of normal females with PCOM in some detail. We compared nonhirsute eumenorrheic volunteers with PCOM (V-PCOM) to both the otherwise entirely similar reference group of females with NOM (V-NOM) and to PCOS, all groups age-matched, using the above protocol (39, 197), as shown in Figure 4.

Healthy adolescent and adult volunteers had similar ovarian function, except that V-NOM adolescents by definition had slightly larger ovaries (volume ≤ 10.8 cc) than V-NOM adults and slightly lower FSH and higher AMH levels (30, 197). V-PCOM are heterogeneous, with a spectrum of ovarian function (Figure 4, C and D). At one end of the V-PCOM spectrum was a subgroup of 40% with an extreme variation of normal size and morphology; they had ovarian androgenic function test results and serum AMH like that of V-NOM (Figure 4, Ca–Da). At the other end of the V-PCOM spectrum, was a subgroup of 22% with “hyperandrogenic PCOM” (V-PCOMh in Figure 4C, b–d); although asymptomatic, they had baseline hyperandrogenemia, and so seemed to meet the definition of ovulatory PCOS (Table 1, phenotype 3) since eumenorrheic; all also had a positive SDAST and/or GnRHag test, which indicates subclinical FOH. They also had mildly increased adrenal androgenic function: DHEAS was 159 ± 58, SD, μg/dL, significantly higher than that of V-NOM (80 ± 41 μg/dL), unlike any other V-PCOM subgroup (P < .01); they also tended to have a higher DHEA response to ACTH (P = .15). DHEAS and DHEA peaks were, respectively, elevated (>180 and > 1100 ng/dL) in 42% and 14% of this subgroup.

Between these extremes lay 2 different kinds of ovarian functional variants (39). On the normal side of the spectrum was a V-PCOM subgroup (10% of V-PCOM) with an isolated AMH elevation (V-PCOM in Figure 4Dd) that indicates increased folliculogenesis. On the PCOS side of the spectrum was a V-PCOM subgroup with “dysregulated PCOM,” ie, steroidogenic hyperresponsiveness to GnRHag (17OHP elevation without hyperandrogenemia) (Figure 4Cd); these constituted 28% of V-PCOM, one-third of whom had mildly elevated serum AMH. It seems probable that this dysregulation indicates a very mild and subclinical degree of intraovarian androgen excess. In a multivariate model, AMH correlated independently across all groups (healthy volunteers with or without PCOM and PCOS) with SDAST testosterone (P = .001), but not peak 17OHP response to GnRHag (P = .5). Summary multiple regression analysis across all groups (Figure 4) shows that serum AMH is independently (R² = 0.3) related to the presence of ovarian hyperandrogenism (P < .001) and to that of PCOM (P = .014).

The picture that emerges from this biochemical spectrum of differences in ovarian function among V-PCOM subjects is that apparently normal women with PCOM occupy a middle position on a spectrum of ovarian function between women with clearly normal ovarian function and those with PCOS (Figure 6). About half have no evidence of steroidogenic dysfunction and, thus, no relation to PCOS. On the other hand, about half of V-PCOM have subclinical evidence of a PCOS-related dysregulation of ovarian steroidogenesis. However, most V-PCOM appear to be ovulatory and at low risk of developing symptomatic PCOS (31, 197, 207, 214, 219). How is this to be interpreted? The subgroup of eumenorrheic young women who have subclinical hyperandrogenemia, which suggests ovulatory PCOS, may well represent a carrier state, or occasionally a risk factor, for PCOS (197), although this remains to be established. The spectrum of ovarian androgenic ovulatory dysfunction may well be wider than ascertained through the presence of PCOM or hyperandrogenemia. Among apparently normal eumenorrheic women, a prospective study indicated that about 8% had sporadic anovulatory cycles and that serum free testosterone and AMH levels were significantly increased in these cycles, although within the normal range (220).

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Figure 6.

Schematic representation of the spectrum of ovarian function found in eumenorrheic nonhirsute V-PCOM (normal-variant PCOM) in relation to that of normal and PCOS women. Approximately 40% of V-PCOM are functionally variations of normal: this group has ovarian function like that of similar V-NOMs. Another 10% of V-PCOM has elevated AMH in the absence of any evidence of ovarian steroidogenic dysfunction, which suggests an isolated increase in folliculogenesis unrelated to ovarian androgenic dysfunction. The remaining half of V-PCOM have some degree of PCOS-related steroidogenic dysregulation, often with AMH elevation. Of these, nearly half (22% of the V-PCOM group) have biochemically hyperandrogenic PCOM, ie, subclinical FOH that suggests ovulatory PCOS. The remainder have isolated dysregulation of ovarian steroidogenesis (ie, isolated in the sense that 17OHP hyperresponsiveness to GnRHag testing occurs in the absence of hyperandrogenemia). Based on data in Figure 4; percentages are averages derived from different denominators for GnRHag test (n = 32) and AMH (n = 28) determinations in V-PCOM.

On the other hand, a substantial minority of our asymptomatic volunteers have isolated (normoandrogenemic) PCOS-like dysregulated steroidogenic function. Many of this subgroup have elevated AMH levels, which is compatible with a very mild degree of intraovarian androgen excess promoting folliculogenesis (79, 143) without interfering with ovulatory function.

Those V-PCOM with AMH elevation, some of whom have absolutely normal steroidogenic function and some of whom have subclinical evidence of steroidogenic dysregulation (Figure 6), are expected to have an increased population of growing follicles (39, 144). Thus, they can be predicted to have a slightly prolonged reproductive lifespan (221).

In conclusion, about half of asymptomatic V-PCOM have evidence of an ovarian steroidogenic dysfunction related to PCOS, including some who seem to have ovulatory PCOS. They are postulated to be carriers for, or at risk for, PCOS.

C. Functional adrenal hyperandrogenism (FAH) in PCOS

Less than 10% of FAH can be accounted for by well-established pathophysiologic entities, the most common of which is nonclassical virilizing congenital adrenal hyperplasia with a prevalence approximating 5% (Table 4). Most FAH is idiopathic (primary), ie, it cannot be incontrovertibly assigned to any of these well-established disorders.

Primary FAH is defined as 17-ketosteroid hyperresponsiveness to ACTH that is otherwise unexplained, which practically speaking involves ruling out steroidogenic blocks (17). The steroidogenic pattern of response to ACTH resembles an exaggerated adrenarche (22). DHEA is the sole hyperresponsive 17-ketosteroid when testing is performed with low-dose ACTH; it was abnormal in 27% of our PCOS series, with similar prevalence in both PCOS-T and PCOS-A (47). DHEA hyperresponses are accompanied by 17-hydroxypregnenolone hyperresponses (r = 0.773), which suggests a relationship between these two entities. Higher-dose ACTH testing yielded a higher prevalence estimate for FAH in PCOS (46%), and androstenedione hyperresponses accounted for most of the difference (22). The pattern of adrenal secretion is compatible with dysregulation of zona reticularis steroidogenesis prominent at the level of the 17-hydroxylase/17,20-lyase activities of P450c17 (Figure 2). The FAH of PCOS is accompanied by an average 50% increase in adrenal volume that correlates with hyperandrogenemia severity (222).

About one-quarter of FOH have the common (primary) type of FAH (Figure 5). This agrees with most estimates of FAH prevalence in PCOS from serum DHEAS measurements (28). However, the magnitude of the DHEAS correlation with DHEA responsiveness to ACTH (r = 0.7) is such that there is considerable nonspecificity in this estimate, which seems due to the high (∼70%) heritability of DHEAS serum levels (223,–225).

D. Other sources of androgen in PCOS

A glandular source of androgen cannot be identified in approximately 8% of hyperandrogenic patients despite thorough testing. Those who present with hirsutism and normal menses, but lack a polycystic ovary, are traditionally given a diagnosis of idiopathic hyperandrogenism.

In our series of PCOS patients who met NIH diagnostic criteria, the subset with no demonstrable ovarian or adrenal dysfunction was obese (Figure 4a and Table 2) (47). We postulated that their excess adipose tissue was both the cause of the testosterone excess (because adipocytes are a site of conversion of circulating androstenedione to testosterone) and the cause of the ovulatory dysfunction (because obesity suppresses LH levels) (83, 226,–229), as discussed below (see section V.B.2). These patients with the PCOS-A of obesity were characterized by mild hyperandrogenemia (normal total testosterone, mildly elevated free testosterone, normal DHEAS, low SHBG), and most had normal-size ovaries, normal LH levels, and normal AMH levels; all had insulin resistance that was similar to that of the other PCOS-A subgroups.

The possibility is unexplored that some cases in whom there is no glandular source of androgen are caused by hereditary defects in the peripheral metabolism of steroids, such that testosterone formation from precursors is excessive.

A. Dysregulation of ovarian function in PCOS

B. Relationship of metabolic syndrome to PCOS

Metabolic syndrome is defined by a cluster of hyperglycemia, central obesity, hypertension, and dyslipidemia. Expression of these individual components can vary between individuals. It ordinarily results from the interactions of insulin resistance and obesity with age (276, 277). Metabolic syndrome occurs in up to one-third of PCOS adolescents and nearly half of PCOS adults (278,–282). Among PCOS patients, an abnormal degree of insulin resistance is reported in about one- to two-thirds (although insulin resistance per se is not a defining feature) (13, 233, 283,–285); obesity prevalence is similar, with considerable variability among populations (1). A number of observations suggest that among obese women with PCOS, metabolic abnormalities related to insulin resistance and obesity are in many instances more important in the mechanism of anovulation in PCOS than androgen excess (286,–288).

Type 2 diabetes mellitus (DM) itself is related to PCOS (289, 290), and deterioration of glucose tolerance can be accelerated in PCOS (291). Glucose intolerance and diabetes arise when β-cell failure compromises the ability of insulin secretion to compensate for insulin resistance. There is a strong heritable component to β-cell dysfunction in women with PCOS (292), and glucose intolerance, ie, β-cell failure, seems to be specifically associated with PCOS-T rather than PCOS-A (47).

C. Relationship of LH excess to PCOS

Increased LH relative to FSH was the first laboratory abnormality identified in classic PCOS. Mean LH levels correlate positively with LH pulse frequency (384, 385). Patients with PCOS have an increased LH pulse frequency, which is particularly striking in overnight studies, because these women typically lack the normal nocturnal slowing of pulse frequency that is the residual effect of ovulation in the previous cycle on the subsequent early follicular phase (384, 402). PCOS LH pulse amplitude is also increased, which is reflected in the size of the pulse induced promptly by GnRH or GnRHag administration (83). Elevated LH levels occur in about half of PCOS patients (197, 384).

Elevated LH has been thought to play a role in the pathogenesis of PCOS by increasing androgen production and secretion by ovarian theca cells (Figure 1). LH is necessary for the expression of gonadal steroidogenic enzymes and sex hormone secretion (Figure 1). Consequently, PCOS is LH dependent (hence, functional), and any treatment or disorder that suppresses LH levels suppresses ovarian steroidogenesis.

However, there are reasons to doubt that serum LH elevation is often the primary cause of FOH. For one, about half of PCOS subjects, particularly obese cases, with a documented ovarian source of hyperandrogenism were demonstrated to have normal baseline and GnRH-stimulated LH levels, as discussed in the previous section (83). For another, normal homologous desensitization of theca cells begins limiting the androgenic response to LH/hCG at submaximal stimulation, as discussed above. Nevertheless, LH is capable of overstimulating steroidogenesis in the presence of the escape from desensitization that occurs with hyperinsulinism. The hyperinsulinism common in PCOS would thus seem to contribute to the frequent ovarian steroidogenic hypersensitivity to LH stimulation (Figure 3). LH excess also seems to play an important role in the PCOS that follows congenital virilization (see section VI).

Recent research also supports the concept that the increase in LH is the result of abnormal sex steroid feedback rather than the cause of androgen excess (83). The elevated mean LH and, particularly, LH pulse frequency, of PCOS are less sensitive to negative feedback by combined estrogen-progestin administration than are those of controls (80, 403). In particular, higher concentrations of progesterone are required to suppress LH pulse frequency in the presence of luteal phase estradiol levels in PCOS (403). Furthermore, sensitivity to estrogen-progestin negative feedback is restored by antiandrogen treatment of PCOS (404). These data indicate that androgen excess interferes with the hypothalamic inhibitory feedback of female hormones, particularly progesterone. This conclusion is supported by a recent reexamination of the effects of testosterone infusion using deconvolution analysis to quantify the pulsatile properties of LH secretion in a 12-hour overnight study, in which 7 normal postmenarcheal and 7 PCOS adolescent girls were tested (405). In normals, when testosterone levels were increased 3-fold (to 120 ng/dL = 4.1nM), LH pulsatile secretion increased 50% (P < .05), whereas basal LH secretion over the 12-hour period did not change. When testosterone levels were raised 6-fold (to 245 ng/dL = 8.5nM), mean serum LH fell 22% (P < .05) due to a fall in basal LH secretion and a return of pulsatile secretion to normal. PCOS adolescents' LH levels were resistant to testosterone: only when testosterone was raised 4-fold to 300 ng/dL (10.4nM) were effects seen: testosterone significantly further increased LH pulsatile secretion and reduced basal LH secretion. Thus, induction of modest hyperandrogenemia appears to stimulate increased LH pulsatility in both normal and PCOS females. It is unclear why the dose-response relationship is shifted in PCOS; it may be due to the different antecedent progesterone or testosterone milieu, or other factors may be involved, for example, in the prenatally androgenized mouse model of PCOS AMH has been shown to directly activate GnRH neurons and increase LH secretion (406).

The androgen effect can be accounted for by increased gonadotrope responsiveness to GnRH: the testosterone elevation of PCOS is associated with enhanced GnRH-stimulated early LH secretion (17, 95, 197, 407). In PCOS, as in normal men, GnRHag administration elicits exaggerated early LH release (Figure 7), reflecting a large gonadotrope pool of readily releasable LH, consistent with this being an effect of the ambient testosterone level (95, 407). However, unlike normal men, and like normal women, GnRHag elicits a subsequent LH surge (Figure 7), which seems to reflect the capacity of female gonadotropes to form the large pool of newly synthesized LH that men are incapable of forming. Notably, GnRHag elicits a lower FSH surge (seemingly secondary to negative feedback by the excessive estrogen and inhibin production), which may contribute to ovulatory inefficiency.

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Figure 7.

Effects of PCOS and sex on response to GnRHag. The early LH responses (1 h after 10-μg/kg GnRHag) of PCOS-T subjects resemble those of normal men (P < .05 vs V-NOM), whereas their surge responses (4 h after GnRHag) resemble those of normal women (P < .001 vs men). The FSH responses of PCOS-T subjects are significantly less than those of V-NOM from 4–24 hours and below those of normal men at 1 and 24 hours after GnRHag (P < .05). PCOS-T and V-NOM are previously reported age-matched groups (47), except NOM in postmenarcheal adolescents has been redefined as mean ovarian volume up to 12.0 cc, consistent with current consensus (30, 51). Adult male data shown for comparison were previously reported using a slightly different GnRHag sampling protocol (407); †, all head-to-head comparisons of normal male and female responses have shown a significant sex difference in the early releasable pool of LH (17, 407).

In summary, the data suggests that the response of LH to androgen is biphasic: mild testosterone excess is stimulatory, severe excess is inhibitory. LH is necessary for the expression of steroidogenic enzymes, and any treatment that suppresses LH levels improves ovarian hyperandrogenism. On the other hand, the phenomenon of homologous desensitization normally limits the role of LH in causing ovarian androgen excess. Thus, the data are compatible with LH excess in PCOS being the result rather than the cause of FOH. However, in the presence of escape from desensitization, such as is induced by hyperinsulinism, ovarian theca cells become more sensitive to LH, which aggravates ovarian hyperandrogenism. For these reasons, and because LH excess is an inconstant feature of PCOS, it is difficult to attribute a primary role to LH excess in the pathogenesis of most PCOS. However, LH excess seems to play a prominent role in the PCOS that follows congenital virilization.

D. Modulation of androgen action in PCOS

Although testosterone appears to be the main circulating androgen (38), the possibility has been raised that atypical adrenal androgens such as 11-ketotestosterone, which has 25% of testosterone's potency, might contribute to androgen action (408). Although serum bioactivity can essentially be accounted for by testosterone in normal women (409), the extent to which such atypical androgens contribute in hyperandrogenic remains to be systematically determined.

The formation of DHT from testosterone by 5αRD is a major determinant of androgen action. Evidence of increased global peripheral 5αRD activity in PCOS has been consistently obtained from evaluation of urinary androgen and cortisol metabolites (250). Indexes of increased 5αRD activity were increased in both nonobese and obese PCOS and significantly greater in the obese than nonobese subjects. The cause is unknown. The possibility of differential expression of “backdoor pathway” enzymes for the formation of DHT, such as 5αRD1/2, α-ketoreductase type 1C2, and 17β-HSD6 (62), in PCOS ovarian theca cells and adrenal zona reticularis cells has been raised by a preliminary report (410). It is possible that the increased 5αRD activity is a consequence of hyperandrogenism because 5αRD activity is up-regulated by androgen action (191, 411). Insulin appears to up-regulate 5αRD activity (250); this effect may be exerted on the type 1 isozyme (412), which in turn up-regulates insulin sensitivity (352, 353). Genetics may play a role, because 5αRD gene variants are associated with PCOS prevalence (413). The increased 5αRD activity has been postulated to play a role in adrenal hyperandrogenism (250). It could also potentiate androgen actions in other organs or tissues, such as the pilosebaceous unit and granulosa cells (77, 412, 413). Serum allopregnanolone, a 5α-reduced progesterone metabolite that is a γ-amino butyric acid receptor agonist, has been reported to be significantly higher in PCOS than in BMI-matched controls (25 vs 17 ng/dL; 0.8 vs 0.5nM) and proposed to play a role in appetite dysregulation (414).

Androgen receptor alternate splice variant heterozygosity has recently been reported in the luteinized granulosa cells of 62% of Han Chinese with PCOS undergoing in vitro fertilization; it is absent in controls (415). Either an insertion or a deletion isoform were coexpressed with wild-type receptor and accounted for the androgen receptor overexpression in these PCOS cells. They reduced nuclear translocation of wild-type receptor, which has an overall negative effect on androgen action. In isolation, neither transduced the normal up-regulation of aromatase by dihydrotestosterone, whereas the insertion variant transduced up-regulation of CYP17A1 by dihydrotestosterone. The expression pattern was tissue specific, not being found in peripheral lymphocytes, where wild-type receptor was found to be up-regulated. The variants were associated with more severe hyperandrogenemia, which was attributed to deficiency of aromatase activity secondary to deficient up-regulation by androgen receptor signaling. They were also associated with lowered expression of genes related to folliculogenesis and ovulation. The mechanism by which these gene variants arise appears to be locally regulated and in part may be epigenetically determined. It has been postulated that these changes are an adaptation of the PCOS ovary to the abnormally hyperandrogenic environment rather than a contributor to the hyperandrogenism (416).

The length of androgen receptor CAG trinucleotide repeats is known to be inversely related to the efficacy of androgen receptor activity. Many studies have examined the associations of polymorphic CAG repeats in the androgen receptor gene, or of X-inactivation favoring short repeats, with PCOS risk, but with inconsistent results (417). A 2013 metaanalysis demonstrated no evident association between the CAG length variations in the AR gene and PCOS risk, whereas the CAG length appeared to be positively associated with testosterone levels in PCOS patients (418).

In summary, although such clinical observations as hirsutism in the apparent absence of hyperandrogenemia and anovulation in association with isolated mild FAH suggest that androgen action may be excessive at the target tissue level in some individuals, information is scarce about the mechanism of such putative effects. Improved knowledge about the role of atypical androgens and postreceptor mechanisms of androgen action will be necessary to understand the role of tissue responsiveness to androgen in PCOS pathogenesis.

A. Heritable traits and genetic linkages

Familial cases of PCOS that appeared to be inherited as an autosomal dominant trait with variable penetrance were recognized long ago (430). Twin studies suggest that there is a strong contribution of familial factors to PCOS pathogenesis (419, 431). In a Dutch twin-family study, the correlation between monozygotic twins for PCOS was 0.71, and for dizygotic twin or nontwin sister pairs, the correlation was 0.38. Heritable traits that have been identified as PCOS risk factors are maternal PCOS, PCOM, hyperandrogenemia, and metabolic syndrome.

B. Intrauterine environment

It is becoming increasingly apparent that environmental insults during development induce persistent changes in the epigenome that lead to altered gene expression and adult disease (461, 462). Congenital virilization and intrauterine nutrition have been incriminated as risk factors for PCOS.

C. Postnatal environment

Postnatal environmental risk factors for PCOS can be viewed as precipitating latent, congenitally programmed susceptibility traits to become manifest.

D. Implications for evolutionary origin of PCOS

PCOS presents an evolutionary paradox; it is very common across populations, although it is an infertility disorder. The classical theories postulate that PCOS developed through natural selection as a spectrum of independent, diverse genetic adaptations that evolved to preserve anabolism and reproductive capacity via increased androgen and insulin production in ancient times of nutritional deprivation, although in current times of plenty this phenotype is disadvantageous (460, 530, 531). An alternate mechanism may be “intralocus sexual conflict,” that is, some PCOS-related genotypes may not disappear because they improve the reproductive fitness of the human male (eg, by promoting male hyperandrogenism) and thus compensate for reduced female fertility (531).

We thank Susan Sam, MD and Annie Newell-Fugate, DVM, PhD, for guidance about the role of insulin and androgen in adipocyte biology.

This research was supported in part by the Eunice Kennedy Shriver National Institute of Child Health and Human Development/National Institutes of Health through Cooperative Agreement U54–041859 as part of the Specialized Cooperative Centers Program in Reproduction and Infertility Research and by National Center For Research Resources Grants RR-00055 and UL1RR024999. Additional support was provided by The University of Chicago Grants DRTC P60-DK20595; and P50 HD057796 (“Sex Steroids, Sleep, and Metabolic Dysfunction in Women”) (to D.A.E.).

Disclosure Summary: The authors have nothing to disclose.