Common Variable Immunodeficiency (CVID) is one of the most common primary immunodeficiencies and is a heterogeneous disorder, both clinically and genetically. CVID patients present with hypogammaglobulinaemia, poor responses to antigens, requiring lifelong IVIG infusions and frequently suffer from infective, autoimmune and malignant complications leading to reduced quality of life and life expectancy. While a genetic defect has been identified for many primary immunodeficiencies, the genetic basis of only 10-15% of CVID patients is known. Here we report a novel mutation in a multiplex kindred with CVID.
Analysis of whole exome sequenced data of two sisters diagnosed with CVID at the age of 10 and 8 (P1 and P2) revealed a novel heterozygous frameshift mutation in NFKB2, resulting in a truncated protein. NF-κB2 is highly evolutionarily conserved and functions in peripheral lymphoid organ development, B cell development and antibody production. Phenotypic analysis revealed a complete absence of B cells in P1 that is not shared by her sister: P2 has a decreased, but detectable number of naïve B cells, and very few memory B cells. This variation is not reported in public databases and is predicted to be damaging. Nfkb2 knockout mice exhibit CVID-like hypogammaglobulinaemia and develop gastric hyperplasia. We are currently investigating the effects of this mutation in Nfkb2 knockout mice to investigate the downstream effects of this mutation.
We have isolated mature B cells from P2 to investigate defects in differentiation of antibody secreting cells and test the sensitivity of her mature naïve B cells that carry the NFKB2 mutation to T-cell dependent stimulation and BAFF activation, assessing if we are observing changes in division, differentiation, death or survival. We assessed the functional consequences of the mutation in this family, by analysing the non-canonical NFKB signaling pathway via p100 processing and nuclear translocation of p52 by Western Blot.