ClinVar Genomic variation as it relates to human health

This alteration is classified as likely benign based on a combination of the following: seen in unaffected individuals, population frequency, intact protein function, lack of segregation with disease, co-occurrence, RNA analysis, in silico models, amino acid conservation, lack of disease association in case-control studies, and/or the mechanism of disease or impacted region is inconsistent with a known cause of pathogenicity.

This sequence change replaces lysine, which is basic and polar, with asparagine, which is neutral and polar, at codon 156 of the NBN protein (p.Lys156Asn). This variant is present in population databases (rs730881858, gnomAD 0.1%), including at least one homozygous and/or hemizygous individual. This missense change has been observed in individual(s) with breast cancer (PMID: 31206626). ClinVar contains an entry for this variant (Variation ID: 182729). Algorithms developed to predict the effect of missense changes on protein structure and function are either unavailable or do not agree on the potential impact of this missense change (SIFT: "Deleterious"; PolyPhen-2: "Possibly Damaging"; Align-GVGD: "Class C0"). In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance.

The frequency of this variant in the general population, 0.0011 (38/34566 chromosomes in Latino/Admixed American subpopulation, http://gnomad.broadinstitute.org), is higher than would generally be expected for pathogenic variants in this gene. In the published literature, the variant has been reported in individuals with breast cancer, as well as unaffected individuals (PMID: 31206626 (2019)), colorectal cancer (PMID: 33359728 (2022)), endometrial adenocarcinoma and synchronous ovarian endometrioid adenocarcinoma (PMID: 32945065 (2021)). Analysis of this variant using bioinformatics tools for the prediction of the effect of amino acid changes on protein structure and function yielded conflicting predictions that this variant is benign or damaging. Based on the available information, we are unable to determine the clinical significance of this variant.

Variant summary: NBN c.468A>C (p.Lys156Asn) results in a non-conservative amino acid change located in the BRCT domain of the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 0.00015 in 251210 control chromosomes, exclusively at a frequency of 0.0011 within the Latino subpopulation in the gnomAD database, including 1 homozygote. This frequency is not significantly higher than expected for a pathogenic variant in NBN causing Nijmegen Breakage Syndrome (0.00015 vs 0.0025), allowing no conclusion about variant significance. c.468A>C has been reported in the literature in an individual with breast cancer, but also healthy controls (e.g. Weitzel_2019). This report does not provide unequivocal conclusions about association of the variant with Nijmegen Breakage Syndrome. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. Six other clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 without evidence for independent evaluation, citing the variant as likely benign (n=1) and uncertain significance (n=5). Based on the evidence outlined above, the variant was classified as uncertain significance.

In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; Observed in individuals with breast cancer or early-onset colorectal cancer, but also in healthy controls (Weitzel et al., 2019; Dharwadkar et al., 2020); This variant is associated with the following publications: (PMID: 32945065, 33359728, 31206626)