Absence of insulin receptor gene mutations in three insulin-resistant women with the polycystic ovary syndrome

The polycystic ovary syndrome: the first 150 years of study

The communities of reproductive medicine and reproductive sciences have been witness to an enormous acceleration of interest in polycystic ovary syndrome (PCO) since the mid-19th century. Although progress has been increasingly palpable, the fundamentals of the etiology and pathophysiology of PCO remain as elusive as ever. Particularly lacking is a requisite understanding of events at the cellular and molecular levels. As we cross the millennial divide, it appears appropriate that an interim progress report be crafted. This treatise is attempting to meet this objective. What follows traces the chronology of the recorded history of PCO in 4 parts.

Female infertility in the era of obesity: The clash of two pandemics or inevitable consequence?

Obesity is an epidemic that has led to a rise in the incidence of many comorbidities: among others, reduced fertility is often under-evaluated in clinical practice. The mechanisms underlying the link between reduced fertility and obesity are numerous, with insulin resistance, hyperglycaemia and the frequent coexistence of polycystic ovary syndrome being the most acknowledged. However, several other factors concur, such as gut microbiome alterations, low-grade chronic inflammation and oxidative stress. Not only do women with obesity take longer to conceive, but in vitro fertilization (IVF) is also less likely to succeed. We herein provide an updated state-of-the-art regarding the molecular bases of what we could define as dysmetabolic infertility, focusing on the clinical aspects, as well as possible treatment.

Deconstructing a Syndrome: Genomic Insights Into PCOS Causal Mechanisms and Classification

Polycystic ovary syndrome (PCOS) is among the most common disorders in women of reproductive age, affecting up to 15% worldwide, depending on the diagnostic criteria. PCOS is characterized by a constellation of interrelated reproductive abnormalities, including disordered gonadotropin secretion, increased androgen production, chronic anovulation, and polycystic ovarian morphology. It is frequently associated with insulin resistance and obesity. These reproductive and metabolic derangements cause major morbidities across the lifespan, including anovulatory infertility and type 2 diabetes (T2D). Despite decades of investigative effort, the etiology of PCOS remains unknown. Familial clustering of PCOS cases has indicated a genetic contribution to PCOS. There are rare Mendelian forms of PCOS associated with extreme phenotypes, but PCOS typically follows a non-Mendelian pattern of inheritance consistent with a complex genetic architecture, analogous to T2D and obesity, that reflects the interaction of susceptibility genes and environmental factors. Genomic studies of PCOS have provided important insights into disease pathways and have indicated that current diagnostic criteria do not capture underlying differences in biology associated with different forms of PCOS. We provide a state-of-the-science review of genetic analyses of PCOS, including an overview of genomic methodologies aimed at a general audience of non-geneticists and clinicians. Applications in PCOS will be discussed, including strengths and limitations of each study. The contributions of environmental factors, including developmental origins, will be reviewed. Insights into the pathogenesis and genetic architecture of PCOS will be summarized. Future directions for PCOS genetic studies will be outlined.

A brief insight into the etiology, genetics, and immunology of polycystic ovarian syndrome (PCOS)

Polycystic ovarian syndrome (PCOS) is a prevailing endocrine and metabolic disorder occurring in about 6-20% of females in reproductive age. Most symptoms of PCOS arise early during puberty. Since PCOS involves a combination of signs and symptoms, thus it is considered as a heterogeneous disorderliness. The most accepted diagnostic criteria is Rotterdam criteria which involves two of the latter three features: (a) hyperandrogenism, (b) oligo- or an-ovulation, and (c) polycystic ovaries. The persistent hormonal imbalance leads to multiple small antral follicles formation and irregular menstrual cycle, ultimately causing infertility among females. Insulin resistance, cardiovascular diseases, abdominal obesity, psychological disorders, infertility, and cancer are also related to PCOS. These pathophysiologies associated with PCOS are interrelated with each other. Hyperandrogenism causes insulin resistance and hyperglycemia, leading to ROS formation, oxidative stress, and abdominal adiposity. In consequence, inflammation, ROS production, insulin resistance, and hyperandrogenemia also increase. Elevation of AGEs in the body either produced endogenously or consumed from diet exaggerates PCOS symptoms and is also related to ovarian dysfunction. This review summarizes how AGE formation, inflammation, and oxidative stress are significantly essential in PCOS progression. Alterations during prenatal development like exposure to excess AMH, androgens, or toxins (bisphenol-A, endocrine disruptors, etc.) may also be the etiologic mechanism behind PCOS. Although the etiology of this disorder is unclear, environmental and genetic factors are primarily involved. Physical inactivity, as well as unhealthy eating habits, has a vital role in the progression of PCOS. This review outlines a collection of specific genes phenotypically linked with PCOS. Furthermore, beneficial effect of metformin in maintaining endocrine abnormalities and ovarian function is also mentioned. Kisspeptin is a protein which helps in onset of puberty and increases GnRH pulsatile release during ovulation as well as role of KNDy neurons in GnRH pulsatile signal required for reproduction are also elaborated. This review also focuses on the immunology related to PCOS involving chronic low-grade inflammation, and how the alterations within the follicular microenvironment are intricated in the development of infertility in PCOS patients. How PCOS develops following antiepileptic and psychiatric medication is also expanded in this review. Initiation of antiandrogen treatment in early age (≤ 25 years) might be helpful in spontaneous conception in PCOS women. The role of BMP (bone morphogenetic proteins) in folliculogenesis and their expression in oocytes and granulosa cells are also explained. GDF8 and SERPINE1 expression in PCOS is given in detail.

Genetic Basis of Polycystic Ovary Syndrome (PCOS): Current Perspectives

Polycystic ovary syndrome (PCOS) is a common infertility disorder affecting a significant proportion of the global population. It is the main cause of anovulatory infertility in women and is the most common endocrinopathy affecting reproductive-aged women, with a prevalence of 8-13% depending on the criteria used and population studied. The disease is multifactorial and complex and, therefore, often difficult to diagnose due to overlapping symptoms. Multiple etiological factors have been implicated in PCOS. Due to the complex pathophysiology involving multiple pathways and proteins, single genetic diagnostic tests cannot be determined. Progress has been achieved in the management and diagnosis of PCOS; however, not much is known about the molecular players and signaling pathways underlying it. Conclusively PCOS is a polygenic and multifactorial syndromic disorder. Many genes have been associated with PCOS, which affect fertility either directly or indirectly. However, studies conducted on PCOS patients from multiple families failed to find a fully penetrant variant(s). The present study was designed to review the current genetic understanding of the disease. In the present review, we have discussed the clinical spectrum, the genetics, and the variants identified as being associated with PCOS. The mechanisms by which variants in the genes confer risk to PCOS and the nature of the physical and genetic interaction between the genetic elements underlying PCOS remain to be determined. Elucidation of genetic players and cellular pathways underlying PCOS will certainly increase our understanding of the pathophysiology of this syndrome. The study also discusses the current status of the treatment modalities for PCOS, which is important to find new ways of treatment.

Perspectives in Polycystic Ovary Syndrome: From Hair to Eternity

CONTEXT

Polycystic ovary syndrome (PCOS) is a common complex genetic disease. It is characterized by hyperandrogenism, gonadotropin secretory changes, polycystic ovarian morphology, and insulin resistance. The etiology of PCOS remains unknown, but modern genetic approaches, such as genome-wide association studies (GWAS), Mendelian randomization, and next-generation sequencing, promise to identify the pathways that are primarily disrupted.

EVIDENCE ACQUISITION

The literature on PCOS, including the author's research, is discussed.

EVIDENCE SYNTHESIS

Recent genetic analyses are reviewed.

CONCLUSIONS

Considerable progress has been made mapping PCOS susceptibility genes. GWAS have implicated gonadotropin secretion and action as important primary defects in disease pathogenesis in European and Han Chinese PCOS cohorts, respectively. European women with the National Institutes of Health and Rotterdam phenotypes as well as those with self-reported PCOS have some gene regions in common, such as chromosome 11p14.1 region containing the FSH B polypeptide (FSHB) gene, suggesting shared genetic susceptibility. Several chromosomal signals are significant in both Han Chinese and European PCOS cohorts, suggesting that the susceptibility genes in these regions are evolutionarily conserved. In addition, GWAS have suggested that DENND1A, epidermal growth factor signaling, and DNA repair pathways play a role in PCOS pathogenesis. Only a small amount of the heritability of PCOS is accounted for by the common susceptibility variants mapped so far. Future studies should clarify the contribution of rare genetic variants and epigenetic factors to the PCOS phenotype. Furthermore, Mendelian randomization can be used to clarify causal relationships, and phenome-wide association studies can provide insight into health risks associated with PCOS susceptibility variants.

Scientific Statement on the Diagnostic Criteria, Epidemiology, Pathophysiology, and Molecular Genetics of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a heterogeneous and complex disorder that has both adverse reproductive and metabolic implications for affected women. However, there is generally poor understanding of its etiology. Varying expert-based diagnostic criteria utilize some combination of oligo-ovulation, hyperandrogenism, and the presence of polycystic ovaries. Criteria that require hyperandrogenism tend to identify a more severe reproductive and metabolic phenotype. The phenotype can vary by race and ethnicity, is difficult to define in the perimenarchal and perimenopausal period, and is exacerbated by obesity. The pathophysiology involves abnormal gonadotropin secretion from a reduced hypothalamic feedback response to circulating sex steroids, altered ovarian morphology and functional changes, and disordered insulin action in a variety of target tissues. PCOS clusters in families and both female and male relatives can show stigmata of the syndrome, including metabolic abnormalities. Genome-wide association studies have identified a number of candidate regions, although their role in contributing to PCOS is still largely unknown.

Genetic variants associated with insulin signaling and glucose homeostasis in the pathogenesis of insulin resistance in polycystic ovary syndrome: a systematic review

BACKGROUND

Polycystic ovary syndrome must be recognized as a serious issue due to its implication on long term health regardless of an individual's age. PCOS and insulin resistance are interlinked, as approximately 40 % of women with PCOS are insulin resistant. However, the detailed molecular basis for insulin resistance that is coupled with PCOS remains poorly understood.

OBJECTIVE

To review the published evidence that polymorphisms in genes that are involved in insulin secretion and action are associated with an increased risk of PCOS.

METHODS

We reviewed articles published through November 2012 which concerned polymorphisms of genes related to insulin signaling and glucose homeostasis as well as their associations with PCOS. The articles were identified via Medline searches.

CONCLUSIONS

No consistent evidence emerged of a strong association between the risk of PCOS and any known gene that is related to insulin signaling and glucose homeostasis. Moreover, recent genome-wide association studies are inconsistent in identifying the associations between PCOS and insulin metabolism genes. Many of the studies reviewed were limited by heterogeneity in the PCOS diagnosis and by not have having a sufficient number of study participants. Further studies are warranted to determine predisposing risk factors which could modify environmental factors and thus reduce the risk of PCOS. Large genome-wide association studies devoted solely to PCOS will be necessary to identify new candidate genes and proteins that are involved in PCOS risk.

Insulin resistance and the polycystic ovary syndrome revisited: an update on mechanisms and implications

Polycystic ovary syndrome (PCOS) is now recognized as an important metabolic as well as reproductive disorder conferring substantially increased risk for type 2 diabetes. Affected women have marked insulin resistance, independent of obesity. This article summarizes the state of the science since we last reviewed the field in the Endocrine Reviews in 1997. There is general agreement that obese women with PCOS are insulin resistant, but some groups of lean affected women may have normal insulin sensitivity. There is a post-binding defect in receptor signaling likely due to increased receptor and insulin receptor substrate-1 serine phosphorylation that selectively affects metabolic but not mitogenic pathways in classic insulin target tissues and in the ovary. Constitutive activation of serine kinases in the MAPK-ERK pathway may contribute to resistance to insulin's metabolic actions in skeletal muscle. Insulin functions as a co-gonadotropin through its cognate receptor to modulate ovarian steroidogenesis. Genetic disruption of insulin signaling in the brain has indicated that this pathway is important for ovulation and body weight regulation. These insights have been directly translated into a novel therapy for PCOS with insulin-sensitizing drugs. Furthermore, androgens contribute to insulin resistance in PCOS. PCOS may also have developmental origins due to androgen exposure at critical periods or to intrauterine growth restriction. PCOS is a complex genetic disease, and first-degree relatives have reproductive and metabolic phenotypes. Several PCOS genetic susceptibility loci have been mapped and replicated. Some of the same susceptibility genes contribute to disease risk in Chinese and European PCOS populations, suggesting that PCOS is an ancient trait.

Microsatellite polymorphism in the fibrillin 3 gene and susceptibility to PCOS: a case-control study and meta-analysis

The D19S884 marker at the fibrillin 3 gene has been analysed as a candidate location for polycystic ovary syndrome (PCOS) mainly in Caucasian descendants. A case-control study was performed with 272 PCOS women and 271 controls to test the hypothesis that variants in the D19S884 marker increase susceptibility to PCOS in Chinese women and a meta-analysis was undertaken to clarify whether there is an allele consistently contributing to the susceptibility. The association analysis showed that PCOS women were significantly different from controls in the distribution of D19S884 allele frequencies. Instead of the well-known A8 allele, the most common allele in Chinese population was proved to be A7, and the allele frequencies of A7 were statistically different between cases and controls (P=0.037). The meta-analysis of A8 and A7 only identified A8 as a significant allelic association at the D19S884 marker in all combined samples (A8: OR 1.391, 95% CI 1.169-1.654; A7: OR 1.154, 95% CI 0.894-1.490). In conclusion, the association study showed a potential association of the D19S884 marker with PCOS in Chinese Han women and the meta-analysis identified that A8 may increase susceptibility to PCOS. Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age, and it affects an estimated 15% of women worldwide based on the Rotterdam criteria. Many studies in Caucasian descendants suggested that variants of the D19S884 marker at the fibrillin 3 gene are associated with the risk of this syndrome. Here we performed a case-control study with 272 PCOS women and 271 controls to investigate whether variants in the D19S884 marker increase susceptibility to PCOS in Chinese women. We also carried out a meta-analysis of some relevant studies to find a more reliable result. Our association analysis showed that PCOS women were significantly different from controls in the distribution of D19S884 allele frequencies, and instead of the well-known A8 (the letter 'A' represents 'allele'), the most common allele in Chinese population was proved to be A7, whose allele frequencies were statistically different between cases and controls. The meta-analysis of A8 and A7 only identified A8 as a significant allelic association at the D19S884 marker in all combined samples. In conclusion, our association study showed a potential association of the D19S884 marker with PCOS in Chinese Han women and the meta-analysis identified that A8 may increase susceptibility to PCOS.

Understanding polycystic ovarian syndrome pathogenesis: an updated of its genetic aspects

Polycystic ovary syndrome (PCOS) is the most frequent cause of female infertility. It is also characterized by metabolic defects that raise the risk for cardiovascular disease. Despite the progress in the definition of the clinical aspects of the syndrome, only very few definite data are available about the ethiopathogenetic mechanisms that subtend PCOS. It is likely that the PCOS phenotype derives from the interaction between environmental and genetic factors. While environmental factors have easily been investigated, the individuation of the genetic factors seem to be more complex. Indeed, PCOS appears to be inherited as a complex, polygenic trait. Several family studies have been conducted with the aim to clarify the genetic aspects of PCOS, but their findings are often conflicting and not conclusive.Moreover, it is difficult to establish with certainty which genes are involved and their effective role in the development of the syndrome because in PCOS, genetic analysis is hampered by low fecundity, lack of a male phenotype, absence of an animal model, and dissimilarity of the diagnostic criteria used to select the patients. Since multiple biochemical pathways are implicated in PCOS pathogenesis, genes of steroid hormone metabolism, gonadotropin release and action, insulin secretion and action, adipose tissue metabolism and others have been investigated. Nevertheless, none of them seems to play a key role in the ethiopathogenesis of PCOS. This article reviews the large body of literature generated to support the presence of genetic abnormalities in PCOS women by taking in consideration the most important studies regarding PCOS candidate genes.

The Genetic Basis of the Polycystic Ovary Syndrome: A Literature Review Including Discussion of PPAR-gamma

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder of the women of reproductive age. Familial clustering of PCOS has been consistently reported suggesting that genetic factors play a role in the development of the syndrome although PCOS cases do not exhibit a clear pattern of Mendelian inheritance. It is now well established that PCOS represents a complex trait similar to type-2 diabetes and obesity, and that both inherited and environmental factors contribute to the PCOS pathogenesis. A large number of functional candidate genes have been tested for association or linkage with PCOS phenotypes with more negative than positive findings. Lack of universally accepted diagnostic criteria, difficulties in the assignment of male phenotype, obscurity in the mode of inheritance, and particularly small sample size of the study populations appear to be major limitations for the genetic studies of PCOS. In the near future, utilizing the genome-wide scan approach and the HapMap project will provide a stronger potential for the genetic analysis of the syndrome.

SNP analysis of follistatin gene associated with polycystic ovarian syndrome

Follistatin has been reported as a candidate gene for polycystic ovarian syndrome (PCOS) based on linkage and association studies. In this study, investigation of polymorphisms in the FST gene was done to determine if genetic variation is associated with susceptibility to PCOS. The nucleotide sequence of human follistatin and the protein sequence of human follistatin were retrieved from the NCBI database using Entrez. The follistatin protein of human was retrieved from the Swiss-Prot database. There are 344 amino acids and the molecular weight is 38,007 Da. The ProtParam analysis shows that the isoelectric point is 5.53 and the aliphatic index is 61.25. The hydropathicity is −0.490. The domains in FST protein are as follows: Pfam-B 5005 domain from 1 to 92; EGF-like subdomain from 93 to 116; Kazal 1 domain, occurred in three places, namely, 118–164, 192–239, and 270–316. There are 31 single-nucleotide polymorphisms (SNPs) for this gene. Some are nonsynonymous, some occur in the intron region, and some in an untranslated region. Two nonsynonymous SNPs, namely, rs11745088 and rs1127760, were taken for analysis. In the SNP rs11745088, the change is E152Q. Likewise, in rs1127760, the change is C239S. SIFT (Sorting Intolerant from Tolerant) showed positions of amino acids and the single letter code of amino acids that can be tolerated or deleterious for each position. There were six SNP results and each result had links to it. The dbSNP id, primary database id, and the type of mutation whether silent and if occurring in coding region are given as phenotype alterations. The FASTA format of protein was given to the nsSNP Analyzer tool, and the variation E152Q and C239S were given as inputs in the SNP data field. E152Q change was neutral and C239S causes disease. Using PANTHER for evolutionary analysis of coding SNPs, the protein sequence was given as input and analyzed for the E152Q and C239S SNPs for deleterious effect on protein function. The genetic association database results showed that FST gene SNPs are linked to PCOS coming under the disease class of metabolic disorders. The list of intronic and synonymous SNPs, with their nucleotide position, amino acid change information, and dbSNP link, is provided for further analysis.

The role of genes in the polycystic ovary syndrome: predisposition and mechanisms

The polycystic ovary syndrome (PCOS), mainly characterized by clinical and/or biochemical hyperandrogenism, ovarian dysfunction and/or polycystic morphology as well as associated metabolic disorders, is the most common endocrine disorder in women of reproductive age. The familial clustering of PCOS cases and the accumulating evidence that the interaction between multiple genetic and environmental factors is necessary for the development of the syndrome, has triggered the conduct of genetic studies on PCOS. These studies have focused on many genetic polymorphisms, investigating their possible positive or negative correlation with the syndrome. The related genes can be grouped in four categories: those related with insulin resistance, those that interfere with the biosynthesis and the action of androgens, those that encode inflammatory cytokines and other candidate genes. Despite the progress that has been made in the elucidation of the genetic mechanisms of the PCOS, the genetic studies on the syndrome still face many obstacles and challenges. Further studies are needed, in order to shed new light in the pathogenesis of the syndrome, which will allow for new approaches in the diagnostics and therapeutics of PCOS.

Genomic variants in polycystic ovary syndrome

The polycystic ovary syndrome (PCOS) is a common disorder in premenopausal women, characterized by the presence, among other traits, of hyperandrogenism, insulin resistance, and hyperinsulinism. The familial aggregation of PCOS lead the interest to the molecular genetic basis of this syndrome, especially to the genes encoding proteins involved in androgen synthesis and the regulation of insulin synthesis and action. Considering the relationship between insulin resistance and chronic inflammation, and the clustering of inflammatory markers in PCOS patients, recent studies focused on the involvement of proinflammatory genotypes on the pathogenesis of PCOS. Mounting evidence suggest at present a complex model of inheritance for PCOS, in which predisposing and protecting genomic variants interact with environmental factors such as obesity and a sedentary lifestyle, finally leading to the classic phenotype of this syndrome. Moreover, the association of hyperandrogenism, insulin resistance and chronic inflammation raised the possibility of an increase risk of cardiovascular disease in women suffering from PCOS. In the present review we will summarize the most important findings published to date regarding the molecular genetic mechanisms underlying the association of PCOS with insulin resistance and chronic inflammation, and the possible interaction of these mechanisms with environmental factors.

The molecular-genetic basis of functional hyperandrogenism and the polycystic ovary syndrome

The genetic mechanisms underlying functional hyperandrogenism and the polycystic ovary syndrome (PCOS) remain largely unknown. Given the large number of genetic variants found in association with these disorders, the emerging picture is that of a complex multigenic trait in which environmental influences play an important role in the expression of the hyperandrogenic phenotype. Among others, genomic variants in genes related to the regulation of androgen biosynthesis and function, insulin resistance, and the metabolic syndrome, and proinflammatory genotypes may be involved in the genetic predisposition to functional hyperandrogenism and PCOS. The elucidation of the molecular genetic basis of these disorders has been burdened by the heterogeneity in the diagnostic criteria used to define PCOS, the limited sample size of the studies conducted to date, and the lack of precision in the identification of ethnic and environmental factors that trigger the development of hyperandrogenic disorders. Progress in this area requires adequately sized multicenter collaborative studies after standardization of the diagnostic criteria used to classify hyperandrogenic patients, in whom modifying environmental factors such as ethnicity, diet, and lifestyle are identified with precision. In addition to classic molecular genetic techniques such as linkage analysis in the form of a whole-genome scan and large case-control studies, promising genomic and proteomic approaches will be paramount to our understanding of the pathogenesis of functional hyperandrogenism and PCOS, allowing a more precise prevention, diagnosis, and treatment of these prevalent disorders.

Genetics of polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is a reproductive system disorder characterized by irregular menses, anovulation, clinical and/or biochemical signs of hyperandrogenism (hirsutism and/or acne), ovarian micropolycystic appearance and metabolic abnormalities, such as hyperinsulinaemia and obesity. The aetiopathogenesis of this syndrome is not well known. Several pathogenetic hypotheses have been proposed to explain the full array of symptoms and signs, but with elusive results. A genetic abnormality causing PCOS is supported by the observation that different members of the same family are often affected, and about half of the sisters of PCOS women have elevated serum testosterone concentrations. Therefore, the presence of gene abnormalities in women with PCOS has been widely explored in the attempt to establish whether their mutations or polymorphisms may cause PCOS. The main genes evaluated are those involved in steroidogenesis, steroid hormone effects, gonadotrophin release regulation and action, insulin secretion and action, and adipose tissue metabolism. Despite the vast body of literature produced, none of the genes evaluated seems to play a key role in PCOS pathogenesis. It is likely that PCOS may represent the final outcome of different, deeply inter-related genetic abnormalities that influence each other and perpetuate the syndrome.

Role of changes in dietary habits in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a heterogeneous clinical condition. In most women, especially in the obese, all features of the metabolic syndrome, particularly insulin resistance and associated hyperinsulinaemia, are present. Insulin is a physiological hormone regulating ovarian function, specifically ovarian steroidogenesis and androgen blood transport and/or activity in the target tissues. Hyperinsulinaemia may therefore play a pivotal role in favouring the hyperandrogenic state and related clinical and metabolic alterations. The abdominal obesity phenotype is common, affecting more than half of PCOS women. Menstrual cycles and fertility rate are negatively affected by the presence of insulin resistance, hyperinsulinaemia and obesity. PCOS women with obesity and insulin resistance are the obvious target for lifestyle intervention, such as changes in dietary habits and increased physical activity. Weight loss should therefore represent the first-line approach in the treatment of obese PCOS women, since it significantly improves hormonal and metabolic abnormalities and may favour spontaneous ovulation and improve fertility rate in the majority of patients. Individualized pharmacological support aimed at favouring weight loss and maintenance and improving insulin resistance may play a complementary role to lifestyle intervention.

A C/T single nucleotide polymorphism at the tyrosine kinase domain of the insulin receptor gene is associated with polycystic ovary syndrome

OBJECTIVE

To examine whether the insulin receptor (INSR) gene contributes to genetic susceptibility to the polycystic ovary syndrome (PCOS).

DESIGN

Case-control study.

SETTING

Academic endocrinology clinic.

PATIENT(S)

Ninety-nine women with PCOS as defined by the National Institutes of Health consensus and polycystic ovaries on ultrasonography, and 136 healthy controls.

MAIN OUTCOME MEASURE

Frequency of genotypes of a single nucleotide polymorphism of the INSR gene in patients and controls.

RESULT(S)

After stratification of participants by body mass index, the frequency of the uncommon T allele of the INSR single nucleotide polymorphism was significantly increased in lean patients with PCOS (body mass index < or =27 kg/m2) compared with lean controls (relative risk, 2.1).

CONCLUSION(S)

The INSR gene is a susceptibility gene for PCOS among lean patients with PCOS. It remains to be determined whether the exon 17 C/T single nucleotide polymorphism is the susceptibility single nucleotide polymorphism for PCOS or whether it is in linkage disequilibrium with another INSR gene polymorphism.

Molecular approach to common causes of female infertility

Pivotal genetic information has been derived for a host of rare genetic disorders, but progress has been much slower in relation to the common causes of female infertility. In this chapter, we shall illustrate the approaches being applied in elucidating conditions causing infertility that are inherited in a polygenic/multifactorial fashion. The task is to determine the number of genes responsible and their chromosomal location(s). The first approach is to use genome-wide quantitative linkage analysis, searching throughout the genome with no prior expectation that a given gene or chromosomal region is casually involved. A second approach is to search across the genome for altered gene expression, for example comparing endometriosis and normal (non-endometriosis)cells. The third approach is less indiscriminate and more focused, depending upon identifying specific candidate genes. Aromatase, calhedrin, oestrogen receptor, galactose-1-phosphate uridyl transferase (GALT) and tumour suppressor genes such as p53 are attractive candidate genes for endometriosis. Endometriosis, which has long been suspected to possess a familial tendency, has been subjected to genome-wide linkage analysis in Oxford, UK, where sib-pair analysis uses polymorphic DNA markers and fluorescence-based automated analysis. Several regions of exclusion have been found, but no linkages have so far been reported. A candidate gene approach focuses on the presence of chromosomal aberrations, the assumption being that endometriosis parallels neoplasia. At Baylor College of Medicine, we thus began by showing chromosome alterations involving trisomy 11, monosomy 16 and monosomy 17 in late-stage endometriosis. A loss of only the p53 tumour suppressor gene, rather than a loss (monosomy) of chromosome 17 per se, however, seems to be the pivotal event. A second representative polygenic/multifactorial disorder causing female infertility is polycystic ovarian syndrome. Both quantitative linkage analysis and candidate gene approaches are being pursued. In the far more commonly observed 'idiopathic' variety (non-adrenal polycystic ovarian syndrome and hirsutism), consensus has long existed that one or more dominant genes causes the condition. Although the mode of inheritance in 'essential' polycystic ovarian syndrome remains uncertain, dominant tendencies are clearly more pertinent than recessive ones. Genes for adrenal biosynthetic enzymes, insulin receptors, leptin and leptin receptors, follistatin, activin and inhibins are attractive candidates for polycystic ovarian disease. A linkage to 37 candidate genes was sought using affected sib-pair analysis and transmission/disequilibrium methods.

Genetic approaches to unraveling reproductive disorders: examples of bedside to bench research in the genomic era

Despite the rapid advances in medical genetics, many clinicians and investigators remain unaware of the general approaches that can be used to map genes. Although there are specific challenges to using genetic approaches in reproductive medicine, the following report summarizes mapping efforts for three diseases: adrenal hypoplasia congenita, hypergonadotropic ovarian failure, and polycystic ovary syndrome. The themes of rare and novel phenotypes, genetically homogenous populations, and genotype/phenotype correlations are emphasized.

Polycystic ovary syndrome in adolescence and early adulthood

Polycystic ovaries and the associated syndrome are recognized as the most common cause of endocrine disturbances in adult women, but much less research has been performed to examine how polycystic ovary syndrome (PCOS) presents in girls and young women. Polycystic ovaries have been demonstrated in childhood, and there is evidence to show that even very young women may show symptoms and signs of the associated syndrome. Closer examination of younger populations (less-than-or-eq, slant 25 years of age), and in particular, studies of girls during the transition from puberty into early adulthood (adolescence), may provide new insights into the pathogenesis and natural history of polycystic ovaries and PCOS, and may indicate whether polycystic ovaries could potentially be considered as a marker for health screening. Consideration should be given to the management of girls and young women with polycystic ovaries and PCOS as this group may have different needs and health risks compared with older women.

Current concepts in the polycystic ovary syndrome

Over the past 20 years, it has been clearly documented that the polycystic ovary syndrome (PCOS) has major metabolic sequelae related to insulin resistance and that insulin resistance plays an important role in the pathogenesis of the reproductive disturbances of the disorder. Family studies have indicated a genetic susceptibility to PCOS. Polycystic ovaries and hyperandrogenemia are present in approximately 50% of sisters of affected women. Increased androgen secretion and insulin resistance persist in cultured theca cells and skin fibroblasts, respectively, from women with PCOS; this finding suggests that these are intrinsic, presumably genetic, defects. Insulin resistance and elevated low-density lipoprotein (LDL) levels also cluster in the sisters of women with PCOS, consistent with genetic traits. Moreover, the brothers of women with PCOS have insulin resistance and elevated dehydroepiandrosterone sulfate (DHEAS) levels, which supports a genetic basis for these findings. Family-based studies of linkage and association have implicated several genes in the pathogenesis of PCOS. The strongest evidence to date points to a gene in the region of the insulin receptor. Insulin-sensitizing therapy mitigates the reproductive disturbances of PCOS.

Hyperinsulinism and its interaction with hyperandrogenism in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. It has become increasingly evident that insulin resistance plays a significant role both as a cause and result of the syndrome. The purpose of this review is to summarize the possible mechanisms leading to insulin resistance and resultant hyperinsulinism (HI) and their interaction with hyperandrogenism (HA) in PCOS. We conducted a computerized search of MEDLINE for relevant studies in the English literature published between January 1966 and January 2000. We reviewed all studies that investigated the roles of insulin, insulin receptor, and insulin gene in insulin resistance and its interaction with hyperandrogenism in PCOS. Insulin resistance in PCOS seems to involve a postbinding defect in the insulin receptor and/or in the receptor signal transduction. Current research has focused on identifying a genetic predisposition for insulin resistance in this syndrome. The answer to the question whether HI or HA is the initiating event is still unclear inasmuch as there are clinical and molecular evidences to support both of these approaches. Our view is that whichever is the triggering insult, a vicious cycle is established where HI acts to aggravate HA and vice versa. In this model, obesity and genetic predisposition seem to be the independent factors that can give rise or contribute to HI, HA, or both simultaneously. It seems that "hyperinsulinemic hyperandrogenism" represents a significant subgroup of PCOS, which probably needs to be renamed and reclassified in the light of this new approach.

Thirty-seven candidate genes for polycystic ovary syndrome: strongest evidence for linkage is with follistatin

Polycystic ovary syndrome (PCOS) is a common endocrine disorder of women, characterized by hyperandrogenism and chronic anovulation. It is a leading cause of female infertility and is associated with polycystic ovaries, hirsutism, obesity, and insulin resistance. We tested a carefully chosen collection of 37 candidate genes for linkage and association with PCOS or hyperandrogenemia in data from 150 families. The strongest evidence for linkage was with the follistatin gene, for which affected sisters showed increased identity by descent (72%; chi(2) = 12.97; nominal P = 3.2 x 10(-4)). After correction for multiple testing (33 tests), the follistatin findings were still highly significant (P(c) = 0.01). Although the linkage results for CYP11A were also nominally significant (P = 0.02), they were no longer significant after correction. In 11 candidate gene regions, at least one allele showed nominally significant evidence for population association with PCOS in the transmission/disequilibrium test (chi(2) >/= 3.84; nominal P < 0.05). The strongest effect in the transmission/disequilibrium test was observed in the INSR region (D19S884; allele 5; chi(2) = 8.53) but was not significant after correction. Our study shows how a systematic screen of candidate genes can provide strong evidence for genetic linkage in complex diseases and can identify those genes that should have high (or low) priority for further study.

Insulin action in the polycystic ovary syndrome

Research on insulin action in PCOS has been intensive after the identification of insulin resistance as a feature of the syndrome in 1980. It is now clear that PCOS is a metabolic as well as a reproductive disorder and an important cause of type 2 diabetes mellitus in women. The cellular and molecular mechanisms of insulin resistance in PCOS are distinct from those in other insulin resistance syndromes. Elucidating these mechanisms promises to provide considerable insight into insulin receptor signal specificity. Conversely, insulin resistance is now known to have an important role in the pathogenesis of the reproductive disturbances of PCOS. It is thought that one or several genetic defects may cause both the insulin resistance and reproductive abnormalities characteristic of PCOS.

Polycystic ovary syndrome

Polycystic ovary syndrome is a syndrome and not a disease. It reflects multiple potential etiologies and variable clinical presentations that are reviewed in this article. In addition to menstrual dysfunction and hyperandrogenism, women with polycystic ovary syndrome also may have hypothalamic-pituitary abnormalities, polycystic ovaries on pelvic ultrasonography, infertility, obesity, and insulin resistance. A familial pattern occurs in some cases, suggesting a genetic component to the disorder. The three major pathophysiologic hypotheses that have been proposed to explain the clinical findings of the disorder as well as treatment options are reviewed in this article.

Understanding the underlying metabolic abnormalities of polycystic ovary syndrome and their implications

Women with polycystic ovary syndrome have an increased rate of obesity, with a propensity toward abdominal deposition of body fat. Independent of obesity, at least half of affected women have insulin resistance. To understand the mechanisms of insulin resistance in polycystic ovary syndrome, it is necessary to understand normal insulin signaling. Women with polycystic ovary syndrome have normal binding of insulin to its receptor but have decreased activation of events downstream of the receptor. This insulin resistance occurs mostly in the peripheral tissues (muscle and fat cells), and results in increased pancreatic insulin secretion to maintain normal glucose levels. Obese women with polycystic ovary syndrome have a relative defect in insulin secretion. At least 20% of obese patients with polycystic ovary syndrome have glucose intolerance or diabetes, versus about 5% of the healthy age-matched population. Obesity and insulin resistance probably increase the risk of cardiovascular disease in women with polycystic ovary syndrome. The metabolic features of polycystic ovary syndrome are important health risk factors and need to be considered seriously, even if the patient seeks treatment for other concerns.

Lack of insulin resistance in fibroblasts from subjects with polycystic ovary syndrome

Insulin resistance in polycystic ovary syndrome (PCOS) is characterized by a novel defect in insulin signal transduction expressed in isolated human adipocytes as impaired insulin sensitivity for glucose transport and antilipolysis. To determine whether this is a generalized defect of a potentially genetic basis, or possibly a tissue-specific one, fibroblast cultures were established from age- and weight-matched obese normal cycling (NC; n = 5) and PCOS (n = 6) subjects. Adipocytes from the current PCOS subjects displayed impaired sensitivity for glucose transport stimulation (half-maximal effective concentration [EC50], 317 +/- 58 pmol/L in PCOS v 130 +/- 40 in NC; P < .025). Specific insulin binding was similar in fibroblasts from NC (0.57% +/- 0.10%/10(6) cells) and PCOS (0.45% +/- 0.10%) subjects. Fibroblasts from NC (4.9- +/- 0.5-fold stimulation) and PCOS (4.6- +/- 0.3-fold) subjects were equally responsive to insulin for stimulation of glucose incorporation into glycogen. Insulin sensitivity for glycogen synthesis in fibroblasts did not differ between NC (EC50, 9.6 +/- 0.9 nmol/L) and PCOS (9.1 +/- 0.9) cells. For thymidine incorporation into DNA, relative insulin responsiveness was similar in NC (2.3- +/- 0.3-fold stimulation) and PCOS (2.1- +/- 0.1-fold) fibroblasts. Insulin sensitivity for DNA synthesis was similar in NC (EC50, 12.9 +/- 2.4 nmol/L) and PCOS (7.6 +/- 1.3) cells. In summary, (1) insulin receptor binding is normal in PCOS fibroblasts; and (2) PCOS fibroblasts have normal insulin sensitivity and responsiveness for metabolic and mitogenic responses. Impaired insulin signal transduction, while present in adipocytes from a group of PCOS subjects, is not found in fibroblasts from the same subjects. This defect is not generalized to all cell types, but may be limited to specific tissues and responses.

Insulin and polycystic ovary syndrome: a new look at an old subject

In recent years the metabolic implications of polycystic ovary syndrome (PCOS) have received a great deal of attention; in fact 50% of women with PCOS are obese and a similar percentage of subjects was found to show exaggerated insulin secretion and reduced insulin-stimulated glucose uptake. The presence of these features in women with PCOS has profound clinical implications in terms of morbidity due to diabetes mellitus, dyslipidemia, hypertension and cardiovascular disease. Moreover, hyperinsulinemia has recently been proposed as a possible independent risk factor for endometrial and breast cancer. In the light of these considerations, the importance of metabolic screening in patients with PCOS in order to improve their quality of life cannot be underestimated. In this review we analyze all the clinical pathologies in which hyperinsulinemia of PCOS could be involved. Furthermore, in order to clarify the possible mechanisms leading to the insulin disorders of the syndrome, we review the available data about the insulin receptor abnormalities, as well as those concerning the insulin resistance and the exaggerated insulin secretion. Finally, we examine the main therapeutic strategies to ameliorate the insulinemic status of PCOS patients in order to potentially be able to prevent the long-term consequences of this syndrome.

Insulin resistance and the polycystic ovary syndrome: mechanism and implications for pathogenesis

It is now clear that PCOS is often associated with profound insulin resistance as well as with defects in insulin secretion. These abnormalities, together with obesity, explain the substantially increased prevalence of glucose intolerance in PCOS. Moreover, since PCOS is an extremely common disorder, PCOS-related insulin resistance is an important cause of NIDDM in women (Table 3). The insulin resistance in at least 50% of PCOS women appears to be related to excessive serine phosphorylation of the insulin receptor. A factor extrinsic to the insulin receptor, presumably a serine/threonine kinase, causes this abnormality and is an example of an important new mechanism for human insulin resistance related to factors controlling insulin receptor signaling. Serine phosphorylation appears to modulate the activity of the key regulatory enzyme of androgen biosynthesis, P450c17. It is thus possible that a single defect produces both the insulin resistance and the hyperandrogenism in some PCOS women (Fig. 19). Recent studies strongly suggest that insulin is acting through its own receptor (rather than the IGF-I receptor) in PCOS to augment not only ovarian and adrenal steroidogenesis but also pituitary LH release. Indeed, the defect in insulin action appears to be selective, affecting glucose metabolism but not cell growth. Since PCOS usually has a menarchal age of onset, this makes it a particularly appropriate disorder in which to examine the ontogeny of defects in carbohydrate metabolism and for ascertaining large three-generation kindreds for positional cloning studies to identify NIDDM genes. Although the presence of lipid abnormalities, dysfibrinolysis, and insulin resistance would be predicted to place PCOS women at high risk for cardiovascular disease, appropriate prospective studies are necessary to directly assess this.

Non-insulin-dependent diabetes mellitus in childhood and adolescence

NIDDM in children and adolescents represents a heterogeneous group of disorders with different underlying pathophysiologic mechanisms. Most subtypes of NIDDM that occur in childhood are uncommon, but some, such as early onset of "classic" NIDDM, seem to be increasing in prevalence. This observed increase is thought to be caused by societal factors that lead to sedentary lifestyles and an increased prevalence of obesity. In adults, hyperglycemia frequently exists for years before a diagnosis of NIDDM is made and treatment is begun. Microvascular complications, such as retinopathy, are often already present at the time of diagnosis. Children are frequently asymptomatic at the time of diagnosis, so screening for this disorder in high-risk populations is important. Screening should be considered for children of high-risk ethnic populations with a strong family history of NIDDM with obesity or signs of hyperinsulinism, such as acanthosis nigricans. Even for children in these high-risk groups who do not yet manifest hyperglycemia, primary care providers can have an important role in encouraging lifestyle modifications that might delay or prevent onset of NIDDM.

New perspectives in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is, perhaps, the most common endocrinopathy affecting premenopausal women. Of such women, 5%-10% have the classic endocrine syndrome of hyperandrogenism and chronic anovulation. The syndrome not only has these long-appreciated reproductive morbidities, but it also has more recently recognized important metabolic consequences related to insulin resistance. This article reviews the current state of the field with respect to the pathogenesis of PCOS and the insulin resistance associated with it.

Excessive insulin receptor serine phosphorylation in cultured fibroblasts and in skeletal muscle. A potential mechanism for insulin resistance in the polycystic ovary syndrome

We investigated the cellular mechanisms of the unique disorder of insulin action found in the polycystic ovary syndrome (PCOS). Approximately 50% of PCOS women (PCOS-Ser) had a significant increase in insulin-independent beta-subunit [32P]phosphate incorporation (3.7-fold, P < 0.05 vs other groups) in skin fibroblast insulin receptors that was present in serine residues while insulin-induced tyrosine phosphorylation was decreased (both P < 0.05 vs other groups). PCOS skeletal muscle insulin receptors had the same abnormal phosphorylation pattern. The remaining PCOS women (PCOS-n1) had basal and insulin-stimulated receptor autophosphorylation similar to control. Phosphorylation of the artificial substrate poly GLU4:TYR1 by the PCOS-Ser insulin receptors was significantly decreased (P < 0.05) compared to control and PCOS-n1 receptors. The factor responsible for excessive serine phosphorylation appeared to be extrinsic to the receptor since no insulin receptor gene mutations were identified, immunoprecipitation before autophosphorylation corrected the phosphorylation defect and control insulin receptors mixed with lectin eluates from affected PCOS fibroblasts displayed increased serine phosphorylation. Our findings suggest that increased insulin receptor serine phosphorylation decreases its protein tyrosine kinase activity and is one mechanism for the post-binding defect in insulin action characteristic of PCOS.

Hyperandrogenic anovulation (PCOS): a unique disorder of insulin action associated with an increased risk of non-insulin-dependent diabetes mellitus

Polycystic ovary syndrome is the most common endocrine disorder in women of reproductive age. Recent prevalence estimates suggest that 5-10% of premenopausal women have the full-blown syndrome of hyperandrogenism, chronic anovulation, and polycystic ovaries. Evidence suggests that women with polycystic ovary syndrome have a unique disorder of insulin action and are at increased risk to develop non-insulin-dependent diabetes mellitus. Further, non-insulin-dependent diabetes mellitus in women with polycystic ovary syndrome has a substantially earlier age of onset (third to fourth decades) than it does in the general population (sixth to seventh decades). Studies assessing whether abnormalities in insulin action are intrinsic or secondary to the hormonal milieu have found that insulin-induced receptor autophosphorylation is markedly diminished in approximately 50% of polycystic ovary syndrome women. This defect is unique to women with polycystic ovary syndrome and is not seen in other common insulin-resistant states of obesity and non-insulin-dependent diabetes mellitus. In polycystic ovary syndrome women who have normal receptor autophosphorylation, it remains likely that signaling mechanisms downstream of the receptor are abnormal, since these women are also insulin resistant. This distinctive post-insulin-binding defect appears to be genetic, since it is present in cells removed from the in vivo environment for generations.