1 Novel Missense Variants in Patients with Primary Immunodeficiency and Immune dysregulation. NFKB1 Missense Variants

Monoallelic mutations in NFKB1 are the most common cause of monogenic primary antibody deficiency (PAD); however, NFKB1 mutations have not been described in rheumatic patients diagnosed with persistent hypogammaglobulinemia following immunomodulatory treatment yet. NFKB1 encodes for the p105 precursor protein, 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. So far, studying the pathogenicity of rare monoallelic NFKB1 variants, including truncating and frameshift mutations, have been shown to cause (haplo)insufficiency, while the functional analysis about missense variants is scarce. We identified a novel missense variant (c.691 C>T, p.R230C) in two German brothers with a history of meningococcal meningitis with sepsis at different time points of their childhood and adolescence late-onset hypogammaglobulinemia. To investigate the pathogenic relevance of this variant, we conducted immunophenotyping and analyzed the ectopic expression in HEK293 cells by confocal imaging and immunoblotting. The ectopic expression of p50 for c.691 C>T restricted transcriptionally active p50 in the cytoplasm. Investigation of immunological parameters of these patients suggested a progressive course of hypogammaglobulinemia, which may partially account for the incomplete penetrance of disease and suggest the need for closer immunological monitoring of those mutation carriers. Additionally, we identified three missense variants (p.R578K, p.R534H, p.E930D) predicted to be deleterious in the C terminal part of p105 in three unrelated rheumatic patients diagnosed with hypogammaglobulinemia secondary to immunomodulatory agents. Overexpression studies showed a reduction in p105/50 expression in all variants by QRT-PCR and immunoblotting. This examination has pointed out that deleterious missense variants in NFKB1 adversely affect the transcriptional and translational activity of NFκB1, impair its function and additionally, emphasized the role of NFKB1 missense variants as a genetic vulnerability for hypogammaglobulinemia in rheumatic patients.