Whole Exome Sequencing of a Consanguineous Turkish Family Identifies a Mutation in GTF2H3 in Brothers With Spermatogenic Failure.

In this case report we describe our investigation into the genetic cause of infertility due to idiopathic nonobstructive azoospermia in a consanguineous Turkish family. We extracted DNA from blood and applied whole exome sequencing on 4 infertile brothers in this family diagnosed with oligo- and azoospermia. Standard bioinformatics analysis pipelines were run including alignment to the reference genome, variant calling, and quality control filtering. Potentially pathogenic variants were identified and prioritized using genetic variant annotation software and public variant frequency databases, followed by validation with Sanger sequencing. A nonsynonymous variant in "general transcription factor TFIIH subunit 3" (GTF2H3) was identified in this consanguineous family. This variant in chromosome 12 (12chr: 124144111 T>C, p.Ser222Pro) of GTF2H3 represents a likely a disease-causing mutation as it is predicted to be damaging, rare, segregates with the disease, and is highly evolutionarily conserved. Familial segregation analysis of the variant showed that it was present as a homozygous mutation in the brothers with nonobstructive azoospermia, and heterozygous mutation in the oligospermic brothers. We propose a mechanism by which this variant leads to deficits in Vitamin A signaling, which is essential for spermatogenesis.

A no-stop mutation in MAGEB4 is a possible cause of rare X-linked azoospermia and oligozoospermia in a consanguineous Turkish family.

PURPOSE: The purpose of this study was to identify mutations that cause non-syndromic male infertility using whole exome sequencing of family cases. METHODS: We recruited a consanguineous Turkish family comprising nine siblings with male triplets; two of the triplets were infertile as well as one younger infertile brother. Whole exome sequencing (WES) performed on two azoospermic brothers identified a mutation in the melanoma antigen family B4 (MAGEB4) gene which was confirmed via Sanger sequencing and then screened for on control groups and unrelated infertile subjects. The effect of the mutation on messenger RNA (mRNA) and protein levels was tested after in vitro cell transfection. Structural features of MAGEB4 were predicted throughout the conserved MAGE domain. RESULTS: The novel single-base substitution (c.1041A>T) in the X-linked MAGEB4 gene was identified as a no-stop mutation. The mutation is predicted to add 24 amino acids to the C-terminus of MAGEB4. Our functional studies were unable to detect any effect either on mRNA stability, intracellular localization of the protein, or the ability to homodimerize/heterodimerize with other MAGE proteins. We thus hypothesize that these additional amino acids may affect the proper protein interactions with MAGEB4 partners. CONCLUSION: The whole exome analysis of a consanguineous Turkish family revealed MAGEB4 as a possible new X-linked cause of inherited male infertility. This study provides the first clue to the physiological function of a MAGE protein.

Exome sequencing reveals a nonsense mutation in TEX15 causing spermatogenic failure in a Turkish family.

Infertility is a global healthcare problem, and despite long years of assisted reproductive activities, a significant number of cases remain idiopathic. Our currently restricted understanding of basic mechanisms driving human gametogenesis severely limits the improvement of clinical care for infertile patients. Using exome sequencing, we identified a nonsense mutation leading to a premature stop in the TEX15 locus (c.2130T>G, p.Y710*) in a consanguineous Turkish family comprising eight siblings in which three brothers were identified as infertile. TEX15 displays testis-specific expression, maps to chromosome 8, contains four exons and encodes a 2789-amino acid protein with uncertain function. The mutation, which should lead to early translational termination at the first exon of TEX15, co-segregated with the infertility phenotype, and our data strongly suggest that it is the cause of spermatogenic defects in the family. All three affected brothers presented a phenotype reminiscent of the one observed in KO mice. Indeed, previously reported results demonstrated that disruption of the orthologous gene in mice caused a drastic reduction in testis size and meiotic arrest in the first wave of spermatogenesis in males while female KO mice were fertile. The data from our study of one Turkish family suggested that the identified mutation correlates with a decrease in sperm count over time. A diagnostic test identifying the mutation in man could provide an indication of spermatogenic failure and prompt patients to undertake sperm cryopreservation at an early age.