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NF-κB1 deficiency is suggested to be the most common cause of common variable immunodeficiency (CVID). NFKB1 encodes for the p105 precursor protein of NF-κB1, which is converted into the active transcriptional subunit p50 through proteasomal processing of its C-terminal half upon stimulation and is implicated in the canonical NF-kB pathway. Rare monoallelic NFKB1 variants have been shown to cause (haplo) insufficiency. Our report describes a novel NFKB1 missense variant (c.691C>T, p.R230C; allele frequency 0.00004953) in a family vulnerable to meningitis, sepsis, and late-onset hypogammaglobulinemia. We investigated the pathogenic relevance of this variant by lymphocyte stimulation, immunophenotyping, overexpression study and immunoblotting. The ectopic expression of p50 for c.691 C>T restricted transcriptionally active p50 in the cytoplasm, and immunoblotting revealed reduced p105/50 expression. This study shows that the deleterious missense variant in NFKB1 adversely affects the transcriptional and translational activity of NFκB1, impairing its function. Patients immunological parameters show a progressive course of hypogammaglobulinemia, which may partially account for the incomplete disease penetrance and suggest the need for closer immunological monitoring of those mutation carriers.

CDK12 is a member of the cyclin-dependent kinase family that acts as regulator of DNA damage response gene expression. A c.1047-2A>G splice site variant of the CDK12 gene was recently reported to strongly associate with hereditary breast and ovarian cancer in patients of Tatar ethnic origin. To gain more insight into the potential risk and the population spread of the c.1047-2A>G variant, we have genotyped three breast cancer case-control series of Tatar, Bashkir and Kazakh ethnicity. We identified c.1047-2A>G in 6/155 cases and 12/362 controls of Tatar ancestry, 0/96 cases and 9/189 controls of Bashkir ancestry, and 1/131 cases and 0/154 controls of Kazakh ancestry (Mantel-Haenszel odds ratio 0.72, 95% CI 0.30–1.70, p = 0.45). Consistent with the absence of a large effect, bioinformatic analyses predicted that c.1047-2A>G modulates alternative splicing of a NAGNAG sequence rather than constituting a loss-of-function allele, and RT-PCR analyses of c.1047-2A>G heterozygous lymphocytes verified the usage of the predicted alternative acceptor site. Our study confirms a high prevalence of CDK12*c.1047-2A>G in the Tatar and Bashkir population but excludes a role as a clinically actionable high-risk breast cancer mutation.