Greg L. Christensen

Identification of polymorphisms and balancing selection in the male infertility candidate gene, ornithine decarboxylase antizyme 3

BackgroundThe antizyme family is a group of small proteins that play a role in cell growth and division by regulating the biosynthesis of polyamines (putrescine, spermidine, spermine). Antizymes regulate polyamine levels primarily through binding ornithine decarboxylase (ODC), an enzyme key to polyamine production, and targeting ODC for destruction by the 26S proteosome. Ornithine decarboxylase antizyme 3 (OAZ3) is a testis-specific antizyme paralog and the only antizyme expressed in the mid to late stages of spermatogenesis.MethodsTo see if mutations in the OAZ3 gene are responsible for some cases of male infertility, we sequenced and evaluated the genomic DNA of 192 infertile men, 48 men of known paternity, and 34 African aborigines from the Mbuti tribe in the Democratic Republic of the Congo. The coding sequence of OAZ3 was further screened for polymorphisms by SSCP analysis in the infertile group and an additional 250 general population controls. Identified polymorphisms in the OAZ3 gene were further subjected to a haplotype analysis using PHASE 2.02 and Arlequin 2.0 software programs.ResultsA total of 23 polymorphisms were identified in the promoter, exons or intronic regions of OAZ3. The majority of these fell within a region of less than two kilobases. Two of the polymorphisms, -239 A/G in the promoter and 4280 C/T, a missense polymorphism in exon 5, may show evidence of association with male infertility. Haplotype analysis identified 15 different haplotypes, which can be separated into two divergent clusters.ConclusionMutations in the OAZ3 gene are not a common cause of male infertility. However, the presence of the two divergent haplotypes at high frequencies in all three of our subsamples (infertile, control, African) suggests that they have been maintained in the genome by balancing selection, which was supported by a test of Tajimas D statistic. Evidence for natural selection in this region implies that these haplotypes may be associated with a trait other than infertility. This trait may be related to another function of OAZ3 or a region in tight linkage disequilibrium to the gene.

Sequence analysis of the X-linked USP26 gene in severe male factor infertility patients and fertile controls

The 1090C>T,L364F variant of the ubiquitin protease 26 (USP26) gene does not appear to be related to male infertility. Mutations of the USP26 gene do not appear to be a common cause of idiopathic azoospermia or severe oligozoospermia.

Analysis of the Meiotic Recombination Gene REC8 for Sequence Variations in a Population with Severe Male Factor Infertility

Proper regulation of meiosis is essential for normal spermatogenesis and abnormalities may be associated with infertility, as shown in both animal knockout studies and studies identifying anomalies in key proteins, such as SCP3 and MLH1. Disruptions of meiosis are associated with azoospermia or severe oligozoospermia, and may increase the incidence of sperm aneuploidy in some men. Based on its function and animal studies, REC8, a key component of the meiotic cohesion complex, has been identified as a candidate male infertility gene. In this study, we have evaluated sequence variation in the REC8 gene of severely infertile men of European descent with azoospermia or severe oligozoospermia compared to a fertile control population. The direct sequencing of these populations revealed nine polymorphic sites, four within intron/exon boarders, four within coding exons and one in the three prime untranslated region. These sites did not show significantly different allelic frequencies in the study populations compared to fertile controls. This indicates that polymorphisms of the Rec 8 gene are not a common cause of infertility in this population. Additional studies are warranted in patients with defined meiotic disruption.