Compound heterozygous mutations in CFTR causing CBAVD in Chinese pedigrees

BACKGROUND: Congenital bilateral absence of the vas deferens (CBAVD) is an important cause of obstructive azoospermia and male infertility. Mutations of CFTR caused the majority of CBAVD cases, and ADGRG2 was recently identified as a new pathogenic gene. Yet, most of the genetic evidence came from sporadic cases, and only one mutation in CFTR can be found in patients. METHODS: In present study, we collected two CBAVD pedigrees, each having two affected male siblings. We performed whole exome sequencing on all patients and validated all potential variants by Sanger sequencing. RESULTS: We excluded ADGRG2 variants but identified compound heterozygous variants of CFTR in both families (NM_000492.3:c.1210‐33_1210‐6GT[13]T[5] and c.4056G>C;p.Gln1352Cys in pedigree 1, c.592G>C;p.Ala198Pro and c.3717G>A;p.Arg1239= in pedigree 2), which were subsequently validated by direct sequencing. c.1210‐33_1210‐6GT[13]T[5] (also known as IVS8‐T5‐TG13) was a known disease‐causing variant causing the skipping of exon 9 of CFTR and inherited from the proband's mother. p.Gln1352Cys and Ala198Pro were rare or novel in public databases and predicted to be deleterious. The p.Arg1239= was a synonymous variant but located at the end of an exon, which was predicted to alter the splicing pattern. CONCLUSION: Our study, in which compound heterozygous variants were identified in two pedigrees, provides more familial evidence that only recessive variants (homozygous or compound heterozygous) in CFTR cause CBAVD. Furthermore, whole exome sequencing may be utilized as a useful tool for mutation screening of genes causing CBAVD.