Screening of the mutations in luteinizing hormone beta-subunit in patients with menstrual disorders

Selfish evolution of placental hormones

We hypothesize that some placental hormones—specifically those that arise by tandem duplication of genes for maternal hormones—may behave as gestational drivers, selfish genetic elements that encourage the spontaneous abortion of offspring that fail to inherit them. Such drivers are quite simple to evolve, requiring just three things: a decrease in expression or activity of some essential maternal hormone during pregnancy; a compensatory increase in expression or activity of the homologous hormone by the placenta; and genetic linkage between the two effects. Gestational drive may therefore be a common selection pressure experienced by any of the various hormones of mammalian pregnancy that have arisen by tandem gene duplication. We examine the evolution of chorionic gonadotropin in the human lineage in light of this hypothesis. Finally, we postulate that some of the difficulties of human pregnancy may be a consequence of the action of selfish genes.

Luteinizing hormone and human chorionic gonadotropin: distinguishing unique physiologic roles

Luteinizing hormone (LH) and human chorionic gonadotropin (hCG) are integral components of the hypothalamic-pituitary-gonadal axis, which controls sexual maturation and functionality. In the absence of signaling through their shared receptor, fetal sexual differentiation and post-natal development cannot proceed normally. Although they share a high degree of homology, the physiologic roles of these hormones are unique, governed by differences in expression pattern, biopotency and regulation. Whereas LH is a key regulator of gonadal steroidogenesis and ovulation, hCG is predominantly active in pregnancy and fetal development. Emerging evidence has revealed endogenous functions not previously ascribed to hCG, including participation in ovulation and fertilization, implantation, placentation and other activities in support of successful pregnancy. Spontaneous and induced mutations in LH, hCG and their mutual receptor have contributed substantially to our understanding of reproductive development and function. The lack of naturally occurring, functionally significant mutations in the β-subunit of hCG reinforce its putative role in establishment of pregnancy. Rescue of reproductive abnormalities resulting from aberrant gonadotropin signaling is possible in certain clinical contexts, depending on the nature of the underlying defect. By understanding the physiologic roles of LH and hCG in normal and pathologic states, we may better harness their diagnostic, prognostic and therapeutic potential.

Association of common LH variant with hyperfunctional promoter in a Japanese infertile woman

A common LH variant (V-LH) with Trp8Arg and Ile15Thr is often associated with ovarian dysfunction primarily in the Japanese population, and the LHB gene encoding V-LH is linked with a hyperfunctional promoter that could partly compensate for the somewhat weak biological effect of the V-LH in the Finnish and other several populations. We analyzed the promoter region in a Japanese infertile woman homozygous for the V-LH, to examine whether the hyperfunctional promoter is present or absent in the Japanese V-LH carriers with ovarian dysfunction. Direct sequencing was performed for a 661 bp promoter region from -8 to -668 bp of LHB, revealing homozygosity for eight nucleotide substitutions (-238A>G, -276G>A, -489C>A, -490T>A, -504T>A, -506T>C, -525T>G, and -552C>T) that are identical to those found in the hyperfunctional promoter. The results suggest that ovarian dysfunction frequently observed in the Japanese V-LH carriers would be due to some population-specific genetic and/or environmental factor(s) rather than to the lack of the hyperfunctional promoter and the resultant low biological effect of the V-LH. In addition, the tight linkage between the two missense substitutions in the coding region and the eight nucleotide substitutions in the promoter region of LHB appears to be common to various ethnic groups.

Frequency of the allelic variant (Trp8Arg/Ile15Thr) of the luteinizing hormone gene in a Brazilian cohort of healthy subjects and in patients with hypogonadotropic hypogonadism

PURPOSE

To evaluate the frequency of allelic variant Trp8Arg/Ile15Thr in the luteinizing hormone beta-subunit gene in a Brazilian population of healthy subjects and in patients with hypogonadotropic hypogonadism.

SUBJECTS AND METHODS

Two hundred and two adults (115 women) with normal sexual function and 48 patients (24 women) with hypogonadotropic hypogonadism underwent a molecular study of the the luteinizing hormone beta-subunit gene using a polymerase chain reaction technique followed by enzymatic digestion with the restriction enzymes Nco I (for detection of the Trp8Arg point mutation) and Fok I (for detection of the Ile15Thr point mutation). Basal luteinizing hormone and FSH, testosterone, or estradiol levels were measured in 37 healthy subjects (21 women) and in 27 hypogonadotropic hypogonadism patients (13 women) by immunofluorometric methods (hLH-Spec and hFSH-Spec, AutoDELFIA, Wallac Oy, Turku, Finland).

RESULTS

The genetic variant of the luteinizing hormone beta-subunit gene was present at a similar frequency in healthy subjects (14.4%) compared to patients with hypogonadotropic hypogonadism (16.6%). There was no effect of the allelic variant of the luteinizing hormone beta-subunit gene on luteinizing hormone levels in patients with hypogonadotropic hypogonadism as compared to healthy subjects.

CONCLUSION

This study indicates that the allelic variant Trp8Arg/Ile15Thr of the luteinizing hormone beta-subunit gene is a common polymorphism in the Brazilian population (14.4%). The same frequency of this luteinizing hormone variant in the groups with hypogonadotropic hypogonadism and in the healthy subjects excludes a relationship between this variant and hypogonadotropic hypogonadism.

Does variant luteinizing hormone (V-LH) predispose to improper testicular position in late pregnancy?

Undescended testes are a common urogenital malformation affecting 2-9% of newborn boys. The etiology of cryptorchidism is probably heterogeneous, but insufficient androgen effect has been recognized as one cause of the condition. A common genetic variant (V) form of LH occurs in apparently healthy individuals universally. Compared with wild-type (WT) LH, the V-LH molecule has increased bioactivity in vitro but shorter half-life in vivo. In the present study, we screened 93 cryptorchid (59 uni- and 34 bilateral) and 211 healthy boys for the occurrence of V-LH to evaluate whether it is related to testicular descent. Two immunofluorometric assays with different combinations of MAb, one detecting WT-LH, the other detecting both WT- and V-LH, were used to measure LH concentrations. The ratio of two LH measurements was used to assess the V-LH status. The prevalence of V-LH was similar in the control and cryptorchid groups, and the total prevalence of V-LH corresponded well to the prevalence of V-LH in general Finnish population. Among cryptorchid boys, the prevalence of V-LH was dependent on gestational age: 6.7% at GA <37, 20.9% at GA 37-39, and 42.9% at GA of 40-42 wk. In contrast, the percentage of V-LH status was similar at different gestational ages in all control groups. We conclude that V-LH is not critical for normal testicular descent but the increased prevalence of V-LH among cryptorchid boys with GA >40, suggests that the lower hormonal efficacy of V-LH predisposes for improper testicular descent in late pregnancy.

Influence of missense mutation and silent mutation of LHbeta-subunit gene in Japanese patients with ovulatory disorders

The frequency of variant LHbeta containing two point mutations (T(986)-C and T(1008)-C) and its relationship to reproductive disorders differ widely between ethnic groups. In a Japanese population, variant luteinizing hormone (LH) correlates with ovulatory disorders. Here we examined the relationship between two missense mutations and five silent mutations (C(894)-T, G(1018)-C, C(1036)-A, C(1098)-T and C(1423)-T) in the LHbeta gene, and ovulatory disorders. We studied 43 patients with ovulatory disorders, 79 patients with normal ovulatory cycles, and 23 healthy men who agreed to join our DNA analysis. PCR-amplified LHbeta-subunit gene sequences were compared with a base sequence of wild-type LH reported after direct sequencing. The highest frequency (0.945) of novel allele was observed at the position of the C(1036)-A transition. No homozygotes for wild-type LHbeta (C(1036)) were identified. The frequency of novel allele in patients with polycystic ovary syndrome, endometriosis, premature ovarian failure and luteal insufficiency was significantly different from that of healthy women. The frequencies of novel alleles (C(894)-T, C(1098)-T and C(1423)-T) in patients with ovulatory disorders were significantly higher than those with normal ovulatory cycles. The mean incidence of point mutation in patients with ovulatory disorders was higher than in those with normal ovulatory cycles. Among patients with variant LH, five silent mutations were identified in 87.5% of patients with ovulatory disorders, whereas only a few silent mutations were identified in patients with normal ovulatory cycles. In a Japanese population, five silent mutations of variant LH could have influenced two missense mutations and/or other unknown missense mutations, causing ovulatory disorders.

Lack of association of the common immunologically anomalous LH with endometriosis

BACKGROUND

Subfertile women with endometriosis have been reported to demonstrate impaired follicular growth, ovulatory dysfunction and disturbed LH patterns. In addition, abnormal LH and/or LH receptors have been linked with endometriosis-associated infertility. Carriers of a variant of the beta-subunit of luteinizing hormone (V-LH) are largely healthy; however, differences in their gonadal function such as alterations in gonadal steroidogenesis, ovarian reserve, pubertal development and predisposition to diseases such as infertility and polycystic ovarian disease have been found.

METHODS AND RESULTS

To explore the possible relationship between endometriosis and V-LH, we examined its frequency in 230 women undergoing laparoscopic surgery for the investigation of infertility. For the entire study population, 185 (80.4%) were wild type; 42 (18.3%) were heterozygous; and three (1.3%) were homozygous for V-LH. No difference was found between women with (n = 85) and without (n = 145) endometriosis concerning the frequency of the type of LH.

CONCLUSION

Our results do not support the hypothesis that the variant form of LH is associated with an altered risk of endometriosis in the population tested.

A common genetic variant of luteinizing hormone; relation to normal and aberrant pituitary-gonadal function

Mutations of the luteinizing hormone (LH) subunit genes are extremely rare. Only one polymorphic LHbeta gene variant makes an exception. In 1992, an immunologically anomalous form of LH was found in a healthy woman, and it was subsequently found to be caused by two point mutations leading to two amino acid substitutions in the LHbeta subunit. Of the two point mutations, Trp(8)Arg and Ile(15)Thr, the first one is mainly responsible for the altered immunoreactivity and the latter one introduces an extra glycosylation site into Asn(13) of the mutated LHbeta peptide. The frequency of this variant LHbeta allele differs widely between ethnic groups, being most common in aboriginal Australians (carrier frequency >50%; allelic frequency 28.3%) and totally lacking from Kotas of Southern India. Functional differences have been detected when wild-type LH and variant LH have been compared. Variant LH possesses increased in vitro bioactivity, whereas its half-life in circulation is shorter in comparison to wild-type LH. Also the regulation of the variant LHbeta gene differs due to additional changes in its promoter sequence. Correlations of occurrence of variant LH with various clinical conditions involving LH function suggest that it represents a biologically less active form of LH and may be related to borderline suppression of gonadal function, including subfertility. In this article, we will review the current information about the differences observed in structure and functions between the wild-type and variant LH, as well as their possible pathophysiological correlations.

Mutations of gonadotropins and gonadotropin receptors: elucidating the physiology and pathophysiology of pituitary-gonadal function

The recent unraveling of structures of genes for the gonadotropin subunits and gonadotropin receptors has provided reproductive endocrinologists with new tools to study normal and pathological functions of the hypothalamic-pituitary-gonadal axis. Rare inactivating mutations that produce distinctive phenotypes of isolated LH or FSH deficiency have been discovered in gonadotropin subunit genes. In addition, there is a common polymorphism in the LHbeta subunit gene with possible clinical significance as a contributing factor to pathologies of LH-dependent gonadal functions. Both activating and inactivating mutations have been detected in the gonadotropin receptor genes, a larger number in the LH receptor gene, but so far only a few in the gene for the FSH receptor. These mutations corroborate and extend our knowledge of clinical consequences of gonadotropin resistance and inappropriate gonadotropin action. The information obtained from human mutations has been complemented by animal models with disrupted or inappropriately activated gonadotropin ligand or receptor genes. These clinical and experimental genetic disease models form a powerful tool for exploring the physiology and pathophysiology of gonadotropin function and provide an excellent example of the power of molecular biological approaches in the study of pathogenesis of diseases.

Association of molecular variants of luteinizing hormone with menstrual disorders

OBJECTIVE

Luteinizing hormone (LH) promotes ovulation and luteinization of the ovarian follicle, and stimulates steroidogenesis in the ovaries. It is known to be present in different molecular forms, and secretion of abnormal LH has been implicated in menstrual disorders and infertility. The purpose of this study was to determine any association of two recently described LH variants with menstrual disorders in Singapore Chinese women. One of these variants had Trp8 to Arg8 and Ile15 to Thr15 replacements in the LH beta-subunit, while the second variant possessed Ser102 substitution for Gly102.

PATIENTS

One hundred and seventy six patients with menstrual disorders and two hundred normal ovulatory women were recruited and screened for the presence of these two LH variants.

METHODS

The polymerase chain reaction (PCR) products of patients were analysed by restriction fragment length polymorphism (RFLP) and the results were compared with those of normal ovulatory women and confirmed by DNA sequencing.

RESULTS

Twenty one (11.9%) patients with menstrual disorders and twenty (10%) normal ovulatory women were found to carry the first variant, but its occurrence did not show any significant statistical difference between the patient and control groups (P = 0.679). However, the second variant was only detected in seven (4%) patients with menstrual disorders, and none of the normal ovulatory subjects (P = 0.005).

CONCLUSIONS

the study showed that the first variant was not associated with menstrual disorders, whereas the second variant might be implicated in menstrual disorders in some Singapore Chinese women.

Mutations and polymorphisms in gonadotropin genes

Mutations in gonadotropin genes are extremely rare. Only one case of inactivating human luteinizing hormone (LH) beta mutation exists in the literature, a male with absence of Leydig cells, lack of spontaneous puberty and infertility. A total of four cases of inactivating mutation of the follicle-stimulating hormone beta (FSHbeta) gene (two female and two male) are known. The phenotype of the women was primary amenorrhea and absence of follicular maturation, the men were azoospermic. In addition, a common genetic variant (v) of LH was recently discovered. It is caused by two point mutations in the LH beta-subunit gene, resulting in amino acid alterations: Trp8 --> Arg and Ile15 --> Thr. In addition, the latter change introduces an extra glycosylation signal for oligosaccharide attachment to Asn13. The v-LHbeta allele has a carrier frequency ranging from 0 to > 50% in various populations. The variant LH molecule has increased intrinsic bioactivity in vitro, but decreased circulatory half-life in vivo, and the v-LHbeta promoter is about 50% more active in cell line transfections than that of wild-type (wt) LH. These differences in LH synthesis and action in individuals homo- or heterozygous for the v-LH allele are reflected by altered disposition to pathologies of pituitary-gonadal function, such as delayed puberty, polycystic ovarian syndrome and infertility.

Alterations in gonadal steroidogenesis in individuals expressing a common genetic variant of luteinizing hormone

Some pathologies of the pituitary-gonadal function have recently been found to be due to mutations of the gonadotropin or gonadotropin receptor genes. Although these conditions are extremely rare, they are very informative, by elucidating some less well characterized facets of normal gonadotropin function and the molecular pathogenesis of disturbances in sexual differentiation and fertility. In contrast, there is a common polymorphism in the Luteinizing Hormone (LH) beta-subunit gene, where two point mutations cause two alterations in the amino acid sequence (Trp8 --> Arg and Ile15 --> Thr) and introduce an extra glycosylation signal to Asn13. The carriers of this variant gene are largely healthy, but certain mild differences in their gonadal function have been found, as reflected by alterations in gonadal steroidogenesis, pubertal development and predisposition to diseases such as infertility, polycystic ovarian syndrome, and breast and prostatic cancer. The purpose of this chapter is to review the current knowledge of the occurrence, special functional features and clinical correlates of this LH variant.

Role of the mutations Trp8 => Arg and Ile15 => Thr of the human luteinizing hormone beta-subunit in women with polycystic ovary syndrome

OBJECTIVE

To evaluate the clinical significance of LH in the form of a mutant beta-subunit in women with polycystic ovary syndrome (PCOS).

DESIGN

Prospective, controlled study.

SETTING

University hospital.

PATIENT(S)

Thirty healthy women and 30 women with PCOS.

INTERVENTION(S)

Clinical, ultrasonographic, and hormonal findings were used to define PCOS. Nucleotide mutations within codons 8 and 15 in the LH beta-subunit gene (Trp8 => Arg and Ile15 => Thr) were analyzed with the use of polymerase chain reaction and subsequent restriction fragment length polymorphism.

MAIN OUTCOME MEASURE(S)

Serum levels of gonadotropins, androgens, E2, and prolactin were determined, and the results of restriction fragment length polymorphism were analyzed.

RESULT(S)

Five women in the control group and one woman in the PCOS group were found to be affected by the LHbeta gene mutations. No difference was observed in serum androgen and E2 levels between the affected women and 25 healthy women who were homozygous for the wild-type LH. However, women whose serum LH levels were < or = 5.1 mIU/mL had a higher risk of having mutant LH.

CONCLUSION(S)

The frequency of LH mutations in women with PCOS is similar to that in healthy women. The presence of the variant does not cause any significant change in serum levels of androgens and E2.

Mutations in human gonadotropin genes and their physiologic significance in puberty and reproduction

OBJECTIVE

Human gene mutations provide an opportunity to study the pathophysiology of the disease process as well as normal physiology. The purpose of the present report was to review known human gene mutations that affect gonadotropin secretion.

DESIGN

A retrospective analysis of studies of human gene mutations that affect hypothalamic, pituitary, and gonadal function was conducted.

RESULT(S)

Mutations have been identified for at least three genes that cause inherited hypogonadotropic hypogonadism. In addition, gene mutations for the beta-subunits of FSH and LH have been characterized. Both activating and inactivating mutations have been identified for the gonadotropin receptor genes.

CONCLUSION(S)

The identification of human gene mutations has furthered our understanding of the normal processes of pubertal development and fertility.

Increased prevalence of luteinizing hormone beta-subunit variant in patients with premature ovarian failure

OBJECTIVE

To evaluate the significance of an LH variant with a mutant beta-subunit (Trp8 to Arg8 and Ile15 to Thr15) in gynecologic disease, including infertility.

DESIGN

Clinical study.

SETTING

Department of Obstetrics and Gynecology, Shimane Medical University Hospital, Izumo, Japan.

PATIENT(S)

Two hundred forty-five Japanese women with endocrine disorders and/or gynecologic disease and 153 healthy, nonpregnant, fertile Japanese women.

INTERVENTION(S)

A blood sample was collected.

MAIN OUTCOME MEASURE(S)

The ratio of LH values from the SPAC-S and Immulyze assays (LH ratio: SPAC-S LH/Immulyze LH) was used to determine variant (< or =0.5) or wild-type (>0.5) LH status according to a demonstrated relation between the ratio and the sequence of the LH beta-subunit gene.

RESULT(S)

The LH ratio was lower (0.80+/-0.31) in the 245 patients than in the controls (1.00+/-0.38), and the variant was more frequent in the patients (18.4%) than in the controls (8.5%). We found no difference in the frequency of the variant between infertile and fertile patients. The prevalence of infertility did not differ between patients with variant LH and patients with normal LH. Ovulatory disorders, hyperprolactinemia, premature ovarian failure, menstrual disorders, and luteal insufficiency were significantly more frequent in patients with the variant.

CONCLUSION(S)

Variant LH may contribute to female reproductive disorders, including infertility and premature ovarian failure.

Determination of a common genetic variant of luteinizing hormone using DNA hybridization and immunoassays

OBJECTIVE

An immunologically anomalous form of LH, due to two point mutations in codons 8 and 15 of the LH beta gene, has previously been described. LH status, i.e. the discrimination between wild-type (WT) and variant (V) LH, is usually determined by immunoassays, which can be unreliable at low serum concentrations of LH. A DNA hybridization assay was therefore developed to score the LH genotype in all subjects, independent of their serum LH concentrations. To evaluate the performance of the hybridization method, and to expand our observations of the worldwide occurrence of the V-LH, we determined its frequency in additional populations. To confirm the connection between the anomalous immunoreactivity and the V-LH beta gene, we also sequenced the LH beta subunit gene of a homozygous person.

DESIGN

According to the ratio of two immunoassays, one detecting only WT-LH and the other detecting equally WT and V-LH, individuals can be classified as homozygotes for the V-LH beta allele, heterozygotes or WT. DNA samples from persons with known LH status, according to the immunoassays, were used for the development and evaluation of a new allele-specific DNA hybridization assay. This assay, and PCR and restriction fragment length polymorphism analysis, were used to determine the frequency of the V-LH beta allele in DNA samples obtained from eight populations.

PATIENTS

Ambulatory adult men and women, apparently healthy and with no endocrine disorders.

RESULTS

The LH genotyping by immunoassays and by the new hybridization method gave identical results with all samples analysed (n = 25). The V-LH beta subunit was observed to always have the two point mutations, and to be identical with the ones previously reported. The V-LH beta carrier frequency in the DNA samples collected from various populations varied between 0 and 53.5%.

CONCLUSIONS

The immunoassay technique and the hybridization assay can be used as alternatives to determine the LH status. A great variation in carrier frequency of the V-LH beta allele is observed in different populations.

A new molecular variant of luteinizing hormone associated with female infertility

OBJECTIVE

To investigate whether the newly described G1502 to A1502 mutation in exon 3 of the LH beta-subunit gene, causing the amino acid substitution of Ser102 for Gly102, is related to female infertility.

DESIGN

Screening of fertile and infertile women for the G1502 to A1502 mutation in the LH beta-subunit gene.

SETTING

Clinics and laboratories of the National University Hospital obstetrics and gynecology department, Singapore.

PATIENT(S)

Two hundred twelve healthy fertile women; 40 infertile women with menstrual disorders, polycystic ovary syndrome, and endometriosis; and 12 women with idiopathic infertility.

INTERVENTION(S)

Exon 3 of the LH beta-subunit gene was analyzed using polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP), and PCR-mediated direct DNA sequencing.

MAIN OUTCOME MEASURE(S)

The PCR products of patients were analyzed by RFLP, and the results were compared with those of fertile controls. DNA sequencing radiographs were compared between two mutation-bearing patients and four controls.

RESULT(S)

The mutation was identified in only two infertile women with endometriosis; other women studied were found to be negative for this mutation.

CONCLUSION(S)

The missense mutation in the LH beta-subunit gene may be implicated in female infertility, possibly endometriosis-associated infertility in some women.