L138ins Variant of the CFTR Gene in Russian Infertile Men

Abstract

(1) Introduction: Pathogenic variants in the CFTR (Cystic Fibrosis Transmembrane conductance Regulator, OMIM: 602421) gene cause Cystic Fibrosis (CF, OMIM: 219700) and CF-related disorders (CF-RD), often accompanied by obstructive azoospermia due to congenital bilateral aplasia of vas deferens (CBAVD, OMIM: 277180) in male patients. The L138ins (c.413_415dup; p. (Leu138dup)) is a mild variant in the CFTR gene that is relatively common among CF-patients in Slavic populations. The frequency of this variant in Russian infertile men has not been sufficiently studied; (2) Materials and Methods: The sample consisted of 6033 Russian infertile men. The patients were tested for 22 common in Russian populations pathogenic variants of the CFTR gene and the IVS9Tn-polymorphic locus of the intron 9. Molecular-genetic studies were performed using amplified fragment length polymorphism (AFLP-PCR), multiplex ligation-dependent probe amplification (MLPA), and nested PCR (for analysis of the IVS9Tn-polymorphic locus); (3) Results: Pathogenic variants in the CFTR were detected in 3.9% of patients. The most frequent variants were F508del and CFTRdele2.3(21kb), accounted for 61.0% and 7.1% of detected variants, respectively. The L138ins variant was detected in 17 (0.28%) individuals: one of them was homozygous, 10 patients were heterozygous, and 6 patients were compound-heterozygous (F508del/L138ins, n = 4; L138ins/N1303K, n = 1; L138ins/5T, n = 1). Two pathogenic CF-causing variants in the CFTR gene were detected in 8 patients, including 7 compound heterozygous (F508del/L138ins, n = 4; F508del/N1303K, n = 1; 2184insA/E92K, n = 1; 3849+10kbC>T/E92K, n = 1) and one homozygous (L138ins/L138ins). The L138ins variant was found in 7 out of 16 (43.75%) chromosomes in six of these patients. The most common pathogenic variant, F508del, was identified in five out of them, in 5 of 16 (31.25%) chromosomes. The allele frequency (AF) of the L138ins variant in the sample has been found to be 0.0014.; (4) Conclusions: The L138ins variant of the CFTR gene is the third most common variant after F508del and CFTRdele2.3(kb) among Russian infertile men.

Pathogenic Variants and Genotypes of the CFTR Gene in Russian Men with Cystic Fibrosis and CBAVD Syndrome

“…In participants (n = 642) from the population-based cohort study ESSE-Vologda, the 394delTT (rs121908769) variant was found to have 0.0047 alleles [20]. This variant of the CFTR gene was found in a large cohort of 6,033 Russian infertile men [14]. However, a heterozygous 394delTT variant was detected in 2 of the 2,146 Russian infertile men examined by Solovyova et al (2018) [21].…”

“…Thus, L138ins was found to be the second most common CFTR gene variant in Russian patients with CBAVD syndrome, and the third in prevalence after F508del and CFTRdele2.3(kb) in Russian infertile men. The allele frequency (AF) of this variant in Russian infertile men (n = 6033) was 0.0014 [14]. The L138ins variant was found as compound heterozygous F508del/L138ins in four CBAVD patients (Table 3).…”

“…A comparative analysis of the prevalence of various CFTR pathogenic variants in the two evaluated groups indicates a similar distribution of their occurrence among both adult men with CF and CBAVD syndrome from the Russian Federation. According to our recent research, ten following CF-causing variants, F508del, CFTRdele2,3, L138ins, W1282X, 1677delTA, 3849+10kbC>T, E92K, 2143delT, G542X, and 2184insA, are more common in Russian infertile men [14]. Their allelic frequency (AF) is 0.0005 or more, and the proportion of each variant is 2% or more of all detected pathogenic CFTR gene variants in both Russian infertile men and CBAVD patients.…”

“…The results of PCR amplification and the allele-specific ligase reaction were evaluated by electrophoresis on an 8% polyacrylamide gel. The methods were previously described in detail [14,15]. Some variants were detected using additional molecular analysis of the CFTR gene using MLPA, DNA sequencing by the Sanger method, or massive parallel sequencing (MPS).…”

Russian Regional Differences in Allele Frequencies of CFTR Gene Variants: Genetic Monitoring of Infertile Couples

“…Pathogenic CFTR gene variants are a cause of cystic fibrosis (CF, OMIM#219700), and CFTR-related disorders (CFTR-RD). Pathogenic variants of the CFTR gene can result in a congenital bilateral absence of the vas deferens, which could be an isolated syndrome (Congenital Bilateral Aplasia (absence) of the Vas Deferens (CBAVD, OMIM# 277180)) or a clinical feature of CF, leading to obstructive azoospermia in 95% of males with CF [5,6]. Moreover, associations between CFTR variants and other forms of male infertility, namely non-obstructive azoospermia and oligozoospermia, were revealed in a recent meta-analysis [7].…”