SCNN1B and CA12 play vital roles in occurrence of congenital bilateral absence of vas deferens (CBAVD)

Abstract

including physical examination, rectal ultrasound examination, and basal hormonal examination. Consequently, aside from the absence of bilateral vas deferens and an elevated sweat chloride concentration (213.50 mmol l−1) detected only in the patient (Figure 1a and 1b), the other examination indexes for the two brothers were normal (Table 1). The study was approved by the Ethical Review Board of West China Second University Hospital, Sichuan University, Chengdu, China. Informed consent was obtained from two brothers in our study. Then, we performed whole-genome sequencing to search for candidate genetic variations responsible for the patient’s phenotype (detailed method can be seen in whole genome sequencing of Supplementary Information). As a result, seven gene mutations, namely, agrin (AGRN), centrosomal protein 104 (CEP104), androglobin (ADGB), neutrophil cytosolic factor 1 (NCF1), polyhomeotic homolog 1 (PHC1), ubiquitin B (UBB), and ribosomal protein S15 (RPS15), were detected only in the patient. Unfortunately, all of them were single nucleotide polymorphisms (SNPs) and synonymous mutations, and all were predicted to be benign by bioinformatic tools including SIFT (http://provean.jcvi.org/seq_submit.php), PolyPhen-2 (http://genetics. bwh.harvard.edu/pph2/index.shtml), and M-CAP (http://bejerano. stanford.edu/MCAP/). Thus, we speculated that the CBAVD in the patient was caused by transcriptome or posttranslational regulation rather than gene mutations. Epigenetic changes can affect gene expression or function independent of changes in DNA sequence. DNA methylation is a crucial epigenetic modification and has been found associated with multiple diseases including cancer, neurodegenerative and cardiovascular disease, and autoimmune syndromes, such as lupus and rheumatoid arthritis (RA). Furthermore, the altered DNA methylation levels of CFTR were found in several CF patients.6 In this study, we further dissected the whole DNA methylation patterns of the two brothers through chip-based 850K whole DNA methylome analysis (Shanghai OE Biotech Inc., Shanghai, China; detailed method can be seen in whole DNA methylome analysis of Supplementary Information). We observed increased levels of DNA methylation on several genes in the patient compared with his sibling; however, after bioinformatics filtering analysis, none of these genes were related to CBAVD (Supplementary Figure 1). Finally, we considered whether there was variation in the transcription levels of CBAVD-related genes between the two Dear Editor, Congenital bilateral absence of the vas deferens (CBAVD), a complete or partial defect of the Wolffian duct derivatives, is found in >25% of men with obstructive azoospermia (OA), but the underlying pathological mechanism remains poorly understood. Previous research has shown that the most common disease associated with CBAVD is cystic fibrosis (CF), the predominant manifestations of which include progressive lung disease, pancreatic dysfunction, elevated sweat chloride electrolyte, meconium ileus, and male infertility.1 CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a cyclic adenosine monophosphate (cAMP)-activated chloride channel protein that plays a vital function in maintaining chloride and bicarbonate homeostasis.2 Therefore, it is generally presumed that the absence of vas deferens is caused by a progressive atrophy related to abnormal electrolyte balance and fluid transport in the male excurrent ducts.3 Approximately 80% of CBAVD cases are caused by CFTR mutations, and mutations of the adhesion G protein-coupled receptor G2 (ADGRG2) gene have recently been found in CBAVD patients;4 however, for the remaining patients, the origin of CBAVD is unknown. Indeed, mutations in several specific gene loci have been confirmed to lead to male infertility, while recent studies have also suggested that most infertility is not caused by simple genetic variations.5 To effectively determine the cause of CBAVD, other pathological mechanisms, such as changes in gene transcriptional levels or epigenetic regulations, should also be considered in CBAVD patients without gene mutations. Here, we report the case of an infertile man with CBAVD in the context of assisted reproductive procedures; interestingly, his monozygotic twin brother did not present this phenotype. Several initial examinations were performed on the patient as well as his brother, LETTER TO THE EDITOR