ClinVar

Description

Variant summary: The CFTR c.1251C>A (p.Asn417Lys) variant involves the alteration of a non-conserved nucleotide. 3/5 in silico tools predict a benign outcome for this variant. This variant was found in 5925/206340 control chromosomes (gnomAD) at a frequency of 0.02871, which is approximately 1.5 times the estimated maximal expected allele frequency of a pathogenic CFTR variant (0.0129603), suggesting this variant is likely a benign polymorphism. However, gnomAD notes that the variant is located in a "segmental duplication region, failed random forests filters, and has an inbreeding coefficient of < -0.03." ExAC, 1790/94952 (frequency: 0.01885) notes that this variant is only covered in 47476 individuals (adjusted allele number = 94952), which is fewer than 80% of the individuals in ExAC, indicating a potentially low-quality site. In addition, each control database, gnomAD and ExAC, show significantly different allele frequencies in each of the subpopulations, making interpretation of the data difficult. Additionally, the relatively high allele frequencies reported by ExAC and gnomAD would be expected to result in homozygous individuals in the population if the allele is benign; however, neither database reports any homozygotes, despite allele frequencies as high as 9-12% in some subpopulations. This may be due to linkage to a nearby pathogenic variant, such as deltaF508, where homozygosity of the variant of interest results in homozygosity of the pathogenic allele, leading to a absence of homozygotes for the variant in the general population. The variant has been reported in the literature without strong evidence for or against causality. In addition, multiple clinical diagnostic laboratories/reputable databases classified this variant as likely benign or benign. Taken together, this variant is classified as a "Variant of Uncertain Significance - Possibly Benign," until additional information becomes available such as higher quality control data and/or functional studies.