Mosaic Ring-like Small Supernumerary Marker Chromosome and Gene Mutation in a Male With Intermittent Azoospermia: A Rare Case Report

Abstract

This study aimed to report a rare case of intermittent azoospermia and ring-like small supernumerary marker chromosomes (sSMCs). An infertile man was diagnosed with azoospermia presenting a normal male phenotype with complete masculinization. Karyotyping and polymerase chain reaction (PCR) were used to detect 16 sequence-tagged sites on the AZF subregions of the Y chromosome, and 115 candidate genes were screened for mutations. Mutations included single nucleotide variations, insertions, and deletions. Metaphase chromosomes were studied by standard trypsin-Giemsa banding; fluorescent in situ hybridization and PCR were performed to analyze specific Y chromosome regions; gene mutations were detected. Chromosomal analysis detected 117 metaphase cells; a mosaicism with marker 1 and marker 2 sSMCs in 2 metaphase cells (47, X, +mar1x2 karyotype), a mosaicism with marker 2 sSMCs in 14 metaphase cells (46, X, +mar2 karyotype), and a mosaicism with marker 1 sSMCs in 76 metaphase cells (46, X, +mar1 karyotype), coexisting with a 45,X cell line in the remaining 25 metaphase cells. PCR analysis showed the sY160 heterochromosome on the AZFc subregion was absent. Next-generation sequencing identified an asthenozoospermia-specific mutation in GAPDHS (rs2293681), and Sanger sequencing verified this mutation. This gene encodes a protein belonging to the glyceraldehyde-3-phosphate dehydrogenase family of enzymes that play an important role in carbohydrate metabolism. Like its somatic cell counterpart, this sperm-specific enzyme functions in a nicotinamide adenine dinucleotide-dependent manner to remove hydrogen and add phosphate to glyceraldehyde 3-phosphate to form 1,3-diphosphoglycerate. During spermiogenesis, this enzyme may play an important role in regulating the switch between different energy-producing pathways, and it is required for sperm motility and male fertility. A mosaic 46, X, +mar1[76]/45, X[25]/46, X, +mar2[14]/47, X, +mar1x2[2] karyotype could be the main explanation for the azoospermia/severe oligospermia, while the likely pathogenic GAPDHS intron mutation may contribute to the symptom of immotile sperms detected in the semen analysis.