Polycystic ovary syndrome (PCOS) is characterized by ovulatory dysfunction and hyperandrogenemia and is accompanied by neuroendocrine abnormalities including increased GnRH pulse frequency, increased LH pulsatility, and relatively decreased FSH, which together contribute to its pathogenesis[1]. A core neuroendocrine mechanism is impaired steroid negative feedback, in which hyperandrogenemia reduces progesterone-mediated inhibition of GnRH pulse frequency, promoting rapid LH pulse secretion and increasing ovarian androgen production[1]. This loss of sex-steroid feedback is thought to arise upstream of GnRH neurons, which lack receptors for oestrogens and progesterone, implicating intermediary neural networks such as the KNDy (kisspeptin/neurokinin B/dynorphin) system that functions as a GnRH pulse generator and shapes GnRH/LH episodicity[2, 3]. In parallel, evidence accumulated over decades indicates functional ovarian hyperandrogenism as an immediate pathophysiologic abnormality in most PCOS, with steroidogenesis dysregulated particularly at CYP17 and amplified by insulin-resistant hyperinsulinism in a substantial subset[4]. Insulin resistance is common and can be independent of obesity, driving compensatory hyperinsulinemia that synergizes with LH to augment theca-cell androgen production and reduce SHBG, thereby increasing bioactive free testosterone[5–7]. PCOS risk is substantially heritable yet polygenic and non-Mendelian, with GWAS-implicated loci in metabolic and neuroendocrine pathways and additional contributions from developmental programming and epigenetic alterations[2, 4, 8]. Chronic low-grade inflammation and oxidative stress also co-occur and may interact with metabolic dysfunction through innate immune signaling and impaired antioxidant defenses[9, 10].
Introduction
PCOS is described as a disorder featuring ovulatory dysfunction and hyperandrogenemia, with neuroendocrine abnormalities that include increased GnRH pulse frequency, increased LH pulsatility, and relatively decreased FSH[1]. Contemporary mechanistic frameworks emphasize that PCOS is not solely an ovarian androgen-excess disorder, because adrenal glands and peripheral tissues are also considered important androgen sources in affected patients[2, 6]. Furthermore, insulin resistance and hyperinsulinemia are well established as associated with PCOS, providing a metabolic axis that links systemic nutrient signaling to ovarian steroidogenesis and neuroendocrine tone[5, 7]. This review synthesizes evidence for interconnected mechanisms spanning neuroendocrine circuitry, androgen biosynthesis, insulin signaling defects, genetic and epigenetic susceptibility, altered folliculogenesis, and inflammatory-oxidative pathways that together can form self-reinforcing pathogenic loops in PCOS[1, 4, 5, 9].
Neuroendocrine mechanisms
PCOS neuroendocrine dysfunction includes increased GnRH pulse frequency, increased LH pulsatility, and relatively decreased FSH, changes that contribute to disease pathogenesis[1]. A key proposed driver is impaired sex-steroid negative feedback: hyperandrogenemia reduces inhibition of GnRH pulse frequency by progesterone, thereby causing rapid LH pulse secretion and increasing ovarian androgen production[1]. More broadly, reduced sex-steroid feedback on GnRH release is proposed to occur upstream of GnRH neurons, because GnRH neurons do not have receptors for oestrogens or progesterone, implying that altered responsiveness resides in upstream neuronal networks[2].
Pulse-generator circuitry
Kisspeptins (encoded by KISS1) act via KISS1R and, in the infundibular nucleus, KNDy neurons function as the GnRH pulse generator and mediate negative feedback from oestradiol[2]. Within this network, kisspeptin serves as an output signal to GnRH neurons that stimulates their activity, while dynorphin acts within the KNDy network to stop synchronization and thereby end GnRH/LH release[3]. These observations support a mechanistic model in which altered KNDy signaling can shift GnRH pulse dynamics toward persistent LH-dominant stimulation of the ovary[1–3].
Androgen and insulin modulation of feedback
Clinical and experimental observations link hyperandrogenemia to reduced progesterone feedback sensitivity, including findings that half of adolescent girls with hyperandrogenemia have impaired GnRH sensitivity to progesterone inhibition similar to adult PCOS[1]. In rodent models, testosterone infusion reduces expression of progesterone receptors required for progesterone-negative feedback and blocks progesterone feedback effects on GnRH release, motivating the hypothesis that high testosterone reduces estradiol-mediated progesterone receptor expression in the hypothalamus[11]. Preclinical work further points to progesterone-sensitive neuronal populations upstream of GnRH neurons, including GABA and KNDy cells, as probable mediators of impaired negative feedback in PCOS[11]. Consistently, resistance to negative feedback appears to relate in part to hyperandrogenemia per se, because it can be reversed by the androgen-receptor antagonist flutamide[12].
Metabolic cues can also modulate this neuroendocrine phenotype because insulin may act directly in the hypothalamus, the pituitary, or both and thereby contribute to abnormal gonadotropin levels[13]. Mechanistically, insulin has a direct action on the pituitary enhancing GnRH-stimulated LH release, with consequent hyperandrogenism resulting from increased LH secretion[13]. Finally, ovarian-derived signals can feed back to the brain: AMH is described as a dual regulator of follicle growth and hypothalamic GnRH secretion, thus creating a vicious cycle, and high AMH can directly stimulate GnRH neuron activity to favor LH release[10].
Hyperandrogenism and androgen biosynthesis
Evidence accrued over the past 30 years indicates that the immediate pathophysiologic abnormality underlying the vast majority of PCOS is functional ovarian hyperandrogenism, and that insulin-resistant hyperinsulinism found in about half of PCOS aggravates it[4]. Steroidogenesis in this context is described as abnormally regulated, particularly at the level of CYP17 (cytochrome P450c17)[4]. The theca-cell abnormality underlying functional ovarian hyperandrogenism appears intrinsic because it persists in response to gonadotropin stimulation after long-term suppression of endogenous gonadotropins and because a steroidogenic defect with overexpression of steroidogenic enzymes (particularly CYP17) can be demonstrated in PCOS theca cells through multiple passages[4].
Ovarian theca-cell steroidogenic signaling
LH stimulates adenylate cyclase via a G-protein–coupled receptor, providing a canonical second-messenger route for steroidogenic activation in theca cells[6]. In response to LH, theca cells convert cholesterol into androgen using CYP11A, CYP17, and 3β-hydroxysteroid dehydrogenase[6]. Hyperandrogenic PCOS is associated with elevated levels of androgens and pro-androgens (including testosterone, androstenedione, and DHEAS) and elevated gene expression related to androgen production (including CYP17, CYP11A, 3β-HSD, and the LH receptor)[6].
Insulin amplification and systemic sources
Hyperinsulinism can counter normal homologous desensitization, upregulating thecal LH receptors and CYP17 activities and thereby aggravating functional ovarian hyperandrogenism[4]. Insulin can also modulate steroidogenesis via its own receptors present on both granulosa and theca cells, supporting direct intra-ovarian insulin signaling as an amplifier of androgen output[13]. At the same time, hyperandrogenism can persist even when ovarian androgen synthesis is suppressed, supporting the contribution of extra-ovarian sources and peripheral activation pathways[10].
Androgens have multiple sources, including ovary, adrenal gland, and adipose tissues, and PCOS is now considered to involve adrenal and peripheral tissues as important androgen sources in addition to the ovaries[2, 6]. In approximately 20% to 30% of cases, there is a concomitant increase in adrenal androgens such as DHEA-S[5]. Mass spectrometry analyses show that 11-oxygenated androgens are the dominant circulating androgens in women with PCOS and correlate substantially with markers of metabolic risk, with their synthesis reliant on peripheral activation of adrenal-derived androgens[2].
Androgen effects on follicle development
Elevated androgens can exert a “folliculotoxic” effect by arresting the growth of primary follicles and preventing maturation into Graafian follicles, providing a direct mechanistic bridge from androgen excess to anovulatory ovarian morphology[5].
Developmental epigenetic programming
Prenatal androgen administration is described as a potent epigenetic regulator that causes transgenerational epigenomic changes in a mouse PCOS model with similarities to those in human PCOS and PCOS daughters, supporting developmental programming as a contributor to sustained hyperandrogenic phenotypes[4].
Insulin resistance and metabolic dysfunction
Insulin resistance is described as a fundamental component of PCOS that is present in both obese and lean phenotypes, although obesity significantly exacerbates its severity[5]. About half of women with PCOS have an abnormal degree of insulin resistance relative to their adiposity, supporting a component that is not fully explained by adiposity alone[4]. Consistently, insulin resistance can be independent of obesity, changes in body composition, and impairment of glucose tolerance[6], and estimates suggest that 50% to 90% of women diagnosed with PCOS have insulin resistance[6].
Insulin resistance, hyperinsulinemia, and androgen excess
Insulin resistance is, by definition, tethered to hyperinsulinemia, and there is a well established association between PCOS, insulin resistance, and hyperinsulinemia[7]. A mechanistic framework proposes that this metabolic abnormality leads to a compensatory increase in circulating insulin, and elevated insulin directly stimulates the ovary and adrenal gland to produce excess androgens, with a positive vicious cycle increasing both hyperinsulinemia and hyperandrogenism[7]. Hyperinsulinemia acts synergistically with LH to augment theca-cell androgen production and simultaneously suppresses hepatic synthesis of SHBG, thereby increasing the fraction of free, biologically active testosterone and worsening clinical features[5]. Additional proposed hyperinsulinemic effects include elevating LH, increasing conversion of androstenedione to testosterone, and reducing LH desensitization at the level of the ovary[14].
Molecular defects in insulin signaling
Intrinsic post-receptor defects in insulin metabolic signaling have been proposed to account for insulin resistance in PCOS in a substantial subset of patients[4]. At the signaling level, increased serine phosphorylation and reduced tyrosine phosphorylation of insulin receptors and IRS1 can impair downstream insulin signal transduction and is described as a primary reason for insulin resistance in PCOS[10]. In adipocytes, GLUT4 expression is reduced in PCOS and GLUT1 expression is not increased in compensation, consistent with impaired glucose transport capacity[10]. In skeletal muscle, decreased circulating adiponectin levels that impair AMPK activity and a decreased response of pyruvate dehydrogenase to insulin stimulation are described as additional drivers of insulin resistance[10].
Ovarian actions of insulin
Insulin interacts synergistically with LH to stimulate androgen production in theca cells, and hyperinsulinemia can increase steroidogenic enzyme expression, especially CYP17, leading to increased androgen output[6]. In granulosa cells, insulin’s synergistic enhancement of LH-induced steroidogenesis could account for arrest of follicle growth with enhanced estradiol production, linking systemic insulin exposure to intra-follicular steroidogenic imbalance[13].
Metabolic sequelae and heterogeneity
Over time, chronic hyperinsulinemia predisposes to metabolic syndrome, non-alcoholic fatty liver disease, and early-onset atherosclerosis, connecting PCOS metabolic dysfunction to longer-term cardiometabolic risk[5]. The metabolic sequelae, particularly insulin resistance and compensatory hyperinsulinemia, are described as creating a feedback loop that sustains ovarian androgen overproduction and contributes to dyslipidemia and glucose intolerance[5]. However, insulin resistance is not a universal feature of PCOS, as indicated by systematic review evidence from hyperinsulinaemic-euglycaemic clamp studies showing lower insulin sensitivity in PCOS than controls (mean effect size −27%) while emphasizing heterogeneity and the potential value of steroid metabolomics for subgrouping[2]. Steroid metabolomics-based phenotyping also suggests that an adrenal-derived androgen group has the highest rates of hirsutism, insulin resistance, and type 2 diabetes, highlighting mechanistic diversity across PCOS presentations[2].
Modifiers and candidate mechanistic targets
Dietary challenges can modulate these pathways because glucose or saturated fat ingestion can aggravate insulin resistance and functional ovarian hyperandrogenism by triggering increased serum levels of proinflammatory factors[4]. Insulin excess can stimulate adipogenesis and abdominal lipogenesis and inhibit lipolysis, leading to adipocyte hypertrophy, which can further modify systemic metabolic and inflammatory signaling[4]. At the signaling pathway level, insulin primarily regulates PI3K/AKT signaling to mediate its metabolic effects in granulosa cells, and insulin sensitizers such as metformin can suppress insulin resistance by regulating the PI3K/AKT pathway, supporting this axis as a mechanistic therapeutic target[15]. More broadly, the glucose and insulin metabolism pathways have been debated regarding whether insulin resistance reflects a defect in insulin action, a primary defect in β-cell function, decreased hepatic clearance of insulin, or combinations thereof, underscoring remaining mechanistic uncertainty[13].
Genetic and epigenetic factors
Twin studies indicate PCOS heritability to be over 70%, supporting a substantial inherited component[4]. Nonetheless, PCOS does not follow a clear Mendelian inheritance pattern, consistent with polygenic risk and phenotypic heterogeneity[8]. Meta-analyses of GWAS indicate that the genetic architecture of PCOS is consistent across diagnostic criteria and ethnic groups, and these observations reinforce the importance of neuroendocrine and metabolic pathways in disease pathogenesis[2].
Polygenic loci and pathway convergence
Robust candidate susceptibility loci are reported near genes in metabolic pathways (including INSR, INS-VNTR, and DENND1A) and neuroendocrine pathways (including FSHR, LH receptor, and THADA), supporting biologic convergence on gonadotropin and insulin-related mechanisms[2]. Consistently, GWAS-led discovery identified a regulatory protein variant proposed to explain typical PCOS secretory abnormalities, DENND1A.V2, illustrating a possible molecular route from genetic variation to altered endocrine output[4].
Developmental programming and missing heritability
GWAS loci currently account for only about 10% of known PCOS heritability (about 70%), suggesting additional influences on disease pathogenesis beyond common-variant associations[2]. In this context, prenatal androgen administration is described as a potent epigenetic regulator that causes transgenerational epigenomic changes in mouse models that resemble human PCOS and PCOS daughters, supporting developmental programming as a mechanism contributing to “missing heritability” and gene–environment interplay[4].
Epigenomic alterations and androgen signaling
Epigenomic alterations in PCOS granulosa cells include >100 differentially methylated sites and abnormal methylation of genes involved in ovarian steroidogenesis (including aromatase), AMH/AMHR signaling, and insulin/IGF signaling, alongside miRNA abnormalities in theca cells and adipose tissue, supporting multi-tissue regulatory remodeling[4]. A mechanistic hypothesis links androgen receptor signaling to neuroendocrine feedback by proposing that activation of the AR complex causes epigenetic modifications of the progesterone receptor gene, leading to repression of progesterone receptor expression, loss of progesterone sensitivity in androgen receptor–expressing GABA neurons, and impaired progesterone negative feedback[16]. Additional epigenetic layers are suggested by findings that FOXO3 expression is increased in non-obese PCOS patients and is related to m6A modification, indicating potential post-transcriptional regulatory involvement[10].
Uncertainties
Because of underpowered studies and complex genetic and phenotypic heterogeneity, the results of many genetic and epigenetic association studies remain inconclusive, emphasizing the need for larger, better-phenotyped cohorts[17]. Furthermore, at least one study reported no significant differences in global DNA methylation between women with PCOS and controls, supporting the possibility that epigenetic effects are locus-specific or tissue-specific rather than global[18].
Ovarian folliculogenesis and dysfunction
In PCOS, an excess of small follicles forms, follicles prematurely luteinize, and few follicles reach the preovulatory stage, accounting for oligo-anovulation and polycystic ovarian morphology (PCOM)[4]. The arrest of follicles at the pre-antral and early antral stages (2–9 mm) gives the ovary its characteristic polycystic appearance on ultrasound, and this morphology is not representative of true cysts but rather a surplus of immature follicles unable to proceed to ovulation due to an androgen-dominant environment[5]. Additionally, the absence of a mid-cycle LH surge, attributed to lack of appropriate estrogenic feedback, results in chronic anovulation and the formation of numerous subcentimeter follicles that fail to reach dominance[5].
AMH and follicle arrest
Elevated serum AMH arises from the increased number of small follicles, and AMH normally acts as a folliculogenesis gatekeeper regulating early follicle growth and development[4]. High AMH levels and increased GnRH pulsatility, with subsequent increased androgen production by theca cells, are described as impairing follicle maturation and resulting in anovulation in PCOS[10]. Mechanistically, high AMH can decrease granulosa cell sensitivity to FSH, linking ovarian follicle composition to diminished FSH-dependent maturation signals[10].
Insulin and gonadotropin interactions within follicles
Insulin can synergistically enhance LH-induced steroidogenesis in granulosa cells, a mechanism proposed to account for follicle growth arrest alongside enhanced estradiol production[13]. In normal ovaries, granulosa cells respond to LH only when follicles reach about 10 mm, whereas in anovulatory PCOS granulosa cells from follicles as small as 4.5 mm respond to LH, supporting premature luteinization responsiveness consistent with altered endocrine-metabolic signaling[13].
Stromal, vascular, and cellular remodeling
Raised circulating levels and ovarian expression of vascular endothelial growth factor contribute to the hypervascular, hyperplastic appearance of ovarian stroma and theca interna in PCOS and might contribute to increased ovarian androgen synthesis[2]. At the cellular level, PCOS is characterized by increased density of small pre-antral follicles and a higher proportion of early growing follicles accompanied by abnormal granulosa cell proliferation, and PCOS is also associated with apoptosis of granulosa cells in antral follicles, supporting a remodeling process that can impair follicle selection and survival[15].
Metabolic and mechanical signaling pathways
In granulosa cells of PCOS patients, glycolysis is enhanced and is described as a marker of activated mTOR signaling and inactivation of AMPK, resulting in excessive activation of primordial follicles and reduction in resting follicle storage[10]. Ovarian mechanical microenvironment is implicated because a rigid ovarian cortex can activate Hippo pathway signaling to inhibit follicles from entering the growth phase and maintain primordial follicles in a dormant state, while fibrotic ECM and a thickened cortex can downregulate Hippo signaling, cause YAP1 over-activation, and lead to stromal hypertrophy and over-proliferation of theca cells[10]. This process is proposed to stimulate hyperplastic theca cells to over-produce androgens and cause multiple small immature follicles to be arrested simultaneously, linking tissue mechanics to androgen excess and follicular arrest[10].
Inflammation and oxidative stress
PCOS has manifestations of chronic inflammation evidenced by increases in CRP, pro-inflammatory cytokines and chemokines, white blood cell count, oxidative stress, and markers of endothelial inflammation, positioning inflammation and oxidative stress as interlinked components of PCOS pathobiology[9]. CRP is an acute-phase reactant produced by hepatocytes under stimulatory control of pro-inflammatory cytokines such as IL-6 and TNFα, and evidence supports CRP as not only a marker but also a mediator of inflammatory processes[9]. For example, CRP can induce endothelial dysfunction and promote MCP-1–mediated chemotaxis, supporting vascular-inflammatory contributions to cardiometabolic risk profiles described in PCOS[9].
Cytokines, innate immunity, and metabolic coupling
Chronic inflammatory processes are associated with elevations of cytokines and chemokines including IL-18, MCP-1, and MIP-1α, and IL-18 is described as closely related to insulin resistance and metabolic syndrome and as a predictor of long-term cardiovascular mortality[9]. Metabolic–immune coupling is supported by the concept that free fatty acids (elevated in obesity) are primary ligands for Toll-like receptors, central regulators of innate immunity[19]. At the receptor–pathway level, with co-receptors CD14 and MD2, TLR4 is activated by pathogen-associated and damage-associated molecular patterns such as LPS, oxLDL, and saturated fatty acid, providing a plausible route from nutrient excess or endotoxin signals to inflammatory activation in PCOS-associated metabolic states[10].
Oxidative stress and antioxidant defenses
Oxidative stress and chronic inflammation are described as closely inter-related, with extensive evidence supporting a vicious cycle in which inflammation induces generation of reactive oxygen species while oxidative stress promotes and aggravates inflammation[9]. Increased production of reactive oxygen species can initiate activation of inflammatory responses in PCOS subjects through mitochondrial damage and dysfunction, reinforcing this oxidative stress–inflammation cycle[20]. Several studies suggest oxidative stress is significantly increased in women with PCOS compared with healthy controls and is correlated with obesity, insulin resistance, cardiovascular disease, hyperandrogenemia, and chronic inflammation[20].
The Keap1/Nrf2 axis provides a counter-regulatory antioxidant program, as Nrf2 activation drives downstream genes that promote synthesis of antioxidant proteins and detoxification enzymes such as HO-1 and NQO-1[10]. However, serum HO-1 levels are reported to be considerably lower in non-obese PCOS patients due to exhaustion, implying reduced antioxidant reserve and altered redox resilience in at least a subset of patients[10].
Limitations of evidence
Interpretation of inflammatory associations is constrained because most studies are cross sectional and thus prohibit determination of causality between adiposity/metabolic risk and chronic inflammation in PCOS[9]. Nonetheless, altered fat distribution and adipocyte dysfunction along with chronic low-grade inflammation have been proposed as a mechanism contributing to increased cardiovascular risk in PCOS, supporting continued study of adipose–immune–ovarian interactions[19].
Discussion
A unifying mechanistic model of PCOS emerges from reciprocal interactions among neuroendocrine drive, androgen excess, and insulin-dependent metabolic amplification[1, 4]. At the neuroendocrine level, impaired steroid negative feedback increases GnRH pulse frequency and LH pulsatility with relatively decreased FSH, and hyperandrogenemia can reduce progesterone inhibition of GnRH pulses, producing rapid LH secretion that increases ovarian androgen production and reinforces upstream dysregulation[1]. KNDy neurons function as a GnRH pulse generator in which kisspeptin provides an output signal to GnRH neurons and dynorphin terminates GnRH/LH release, providing specific circuit nodes through which steroid feedback alterations can affect pulsatility patterns[2, 3]. Androgen-mediated impairment of progesterone receptor expression and upstream progesterone-sensitive GABA/KNDy networks, plus reversal of feedback resistance by androgen receptor antagonism in supportive models, together support a feed-forward neuroendocrine loop driven by androgen signaling[11, 12].
At the ovarian level, functional ovarian hyperandrogenism is proposed as an immediate abnormality in most PCOS, characterized by dysregulated steroidogenesis particularly at CYP17 and intrinsic theca-cell overexpression of steroidogenic enzymes across passages, aligning with sustained hyper-responsiveness to gonadotropin stimulation[4]. Hyperinsulinemia can upregulate thecal LH receptors and CYP17 activities and synergize with LH to increase theca androgen production while suppressing SHBG and increasing free testosterone, thereby coupling metabolic insulin exposure to androgen bioavailability and ovarian steroid output[4, 5]. Because hyperandrogenism can persist even when ovarian androgen synthesis is suppressed and because androgens can arise from ovary, adrenal gland, and adipose tissue (including dominant circulating 11-oxygenated androgens dependent on peripheral activation), systemic androgen ecology likely determines phenotype severity in many patients[2, 6, 10].
Ovarian morphology and anovulation can be interpreted as downstream consequences of these upstream loops because PCOS features an excess of small follicles, premature luteinization, and failure to reach the preovulatory stage, and elevated androgens can arrest follicle growth (“folliculotoxic” effects)[4, 5]. AMH provides a mechanistic bridge between follicle composition and neuroendocrine dysregulation, because AMH is described as a dual regulator of follicle growth and hypothalamic GnRH secretion that can create a vicious cycle by stimulating GnRH neuron activity and favoring LH release while decreasing granulosa sensitivity to FSH[10]. Metabolic-inflammation pathways further modulate this system: cytokines, endotoxin-related ligands, and oxidative stress are interrelated, and oxidative stress can promote inflammation in a vicious cycle, plausibly exacerbating insulin resistance and thereby feeding back into the insulin–LH–androgen axis described in PCOS[5, 9, 10].
The table below summarizes central self-reinforcing loops supported in the cited mechanistic literature.
Genetic and epigenetic susceptibility provides an upstream substrate that may modulate the strength and tissue specificity of these loops, because PCOS heritability exceeds 70%, loci cluster in metabolic and neuroendocrine pathways, GWAS explains only a minority of heritability, and epigenomic alterations are reported in granulosa cells and in androgen and insulin-related pathways[2, 4]. Remaining challenges include heterogeneity (for example, insulin resistance is not universal) and limitations of cross-sectional inflammatory studies, indicating that the directionality and primary initiating defect likely differ across individuals and require mechanistically anchored patient stratification approaches such as steroid metabolomics[2, 9].
Conclusion
Mechanistic evidence supports PCOS as a systems-level disorder in which neuroendocrine abnormalities (rapid GnRH and LH pulsatility with relatively decreased FSH) interact with impaired steroid negative feedback to drive ovarian androgen production[1]. Functional ovarian hyperandrogenism, characterized by dysregulated steroidogenesis particularly at CYP17 and intrinsic theca-cell abnormalities, provides a proximate endocrine source of hyperandrogenemia that can be amplified by hyperinsulinemia through upregulated LH receptor/CYP17 activity and reduced SHBG[4, 5]. Insulin resistance, often present across obese and lean phenotypes and tethered to hyperinsulinemia, is underpinned by post-receptor signaling defects and altered phosphorylation states and glucose transport biology, linking metabolic impairment to reproductive dysfunction through the insulin–LH–theca axis[5–7, 10]. Genetic susceptibility is substantial and polygenic, with GWAS-implicated loci in metabolic and neuroendocrine pathways, while developmental programming and epigenetic modifications offer plausible mechanisms for missing heritability and persistent pathway re-tuning[2, 4]. Finally, chronic low-grade inflammation and oxidative stress co-occur and can form a vicious cycle connected to innate immune activation and impaired antioxidant defenses, potentially worsening metabolic risk and thereby indirectly reinforcing endocrine abnormalities[9, 10]. Future work should prioritize mechanistic stratification of PCOS subtypes, integrating endocrine pulsatility, steroid metabolomics, insulin signaling phenotypes, and tissue-resolved epigenomic and immune-redox profiling to clarify causality and identify subtype-specific therapeutic targets[2, 13, 17].
