No association between polymorphisms in PTEN and primary ovarian insufficiency in a Han Chinese population

There are two mechanisms that are involved in the occurrence of POI: follicle dysfunction and follicle premature exhaustion [3]. Follicle premature exhaustion indicates the accelerated apoptosis of primordial follicles or premature activation of primordial follicles. Therefore, the survival of primordial follicles is necessary for normal ovarian function. Early researchers inferred that there are inhibitory factors in intact ovarian tissue that maintain the majority of primordial follicles in a dormant state [12]. Previous studies have demonstrated that the PI3K signal pathway is one of the crucial molecular mechanisms that are involved in the survival, dormancy and apoptosis of mammalian primordial follicles [13]. Multiple signal molecules of this pathway were recognised as either stimulating factors (such as Ribosomal protein S6) or inhibitory factors (such as tuberous sclerosis complex 1 and tuberous sclerosis complex 2) in maintaining the balance of the activation and dormancy of mammalian primordial follicles [13, 14]. PTEN down-regulates the PI3K signal pathway [13]. The functional deficiency or dysfunction of Pten leads to continuous and excessive activation of the downstream signal pathway and results in excessive activation and depletion of primordial follicles, ultimately leading to ovarian failure in mice [13, 14]. Before the complete depletion of primordial follicles, Pten mutant mice undergo normal ovulation and generate normal offspring [15, 16].

In the present study, we sought to study the relationship between seven SNPs (rs1234219, rs1903858, rs2299939, rs35352882, rs17107001, rs2299941 and rs12572106) in PTEN and POI in 148 POI patients and 230 controls. We performed an association analysis of the seven SNPs with regard to their allele frequencies, genotype frequencies and haplotype distributions. Rs2299939 showed a statistically significant difference in allele frequency, but the difference disappeared after Bonferroni correction. Haplotype T-T-A-A-T showed an association with POI, but it too disappeared after 10⁴ permutation tests.

POI is a complex disease that involves multiple genes. Although many genes have been confirmed as being involved in the development of POI [2], the cause of most cases remains unidentified. Therefore, many investigators have devoted their research to identifying the aetiology of POI. Because previous studies have found that the deletion of PTEN in oocytes leads to the failure of ovarian function in mice [5], we sought to determine whether PTEN is involved in the incidence and development of human POI. We did not find an association between POI and any risk alleles, genotypes or haplotypes. There are several possible explanations for these results. First, PTEN has never been demonstrated to be associated with human POI. In addition, specific differences between mice and humans may account for genetic differences in the PTEN region. Although researchers have found that compared to mice more primordial follicles were activated in human ovarian cortical fragments after treatment with a PTEN inhibitor [9], they did not analyse the statistical significance of the difference. In addition, that study’s sample size may not have been sufficiently large. In the previous study, the increased gonadotropin concentrations, morphological changes of the ovary and the depletion of primordial follicles began to appear 12 weeks postnatal in PTEN mutant mice. In humans, the period from birth to puberty may last over 10 years. If the gene mutation or abnormal function of PTEN occurs in the embryonic or early life, it is likely that ovarian primordial follicles may be activated and exhausted before puberty, which may present as primary amenorrhea. If the gene mutation or abnormal function of PTEN occurs after puberty, it behaves as secondary amenorrhea. Therefore, we divided the cases into primary and secondary amenorrhea and early and late amenorrhea and compared the patients with the controls. If we obtained meaningful results, we could affirm the association between PTEN and POI and could also infer the approximate time of the PTEN mutation. Rs2299939 showed a statistically significant difference between these groups in allele frequency, but the difference disappeared after Bonferroni correction. The primary amenorrhea sample size was too small. A larger sample size of primary amenorrhea POI patients may yield statistically significant results, especially considering the promising rs2299939 allele and T-T-A-A-T haplotype.

Researchers analysed the PCR products of the PTEN encoding region via direct sequencing in 20 idiopathic POI patients and 20 controls, but found no meaningful mutation [17]. We hypothesise that a larger sample size may improve results, and in population genetics, many different results are due to the varied composition of the studied populations. Chinese scientists had already performed a mutation analysis of nine exons of PTEN in 161 Chinese women with POI but did not observe any mutations or variants [18]. The sample size of their study was similar to the sample size used in the present study, and they researched PTEN from various angles, performing mutational analysis of exons and conducting an association study of intronic SNPs. The two studies mutually remedy their respective defects and together indicate that PTEN may not participate in the pathogenesis of POI. In addition, the POI patients in the two studies were all secondary amenorrhea patients. Thus, we need to confirm the results in a larger sample of patients with primary amenorrhea.