Identification of 22 novel BTK gene variants in B cell deficiency with hypogammaglobulinemia.

X-linked agammaglobulinemia (XLA) is an inborn error of immunity caused by pathogenic variants in the BTK gene, resulting in impaired B cell differentiation and maturation. Over 900 variants have already been described in this gene, however, new pathogenic variants continue to be identified. In this report, we describe 22 novel variants in BTK, associated with B cell deficiency with hypo- or agammaglobulinemia in male patients or in asymptomatic female carriers. Genetic data was correlated with BTK protein expression by flow cytometry, and clinical and family history to obtain a comprehensive assessment of the clinico-pathologic significance of these new variants in the BTK gene. For one novel missense variant, p.Cys502Tyr, site-directed mutagenesis was performed to determine the impact of the sequence change on protein expression and stability. Genetic data should be correlated with protein and/or clinical and immunological data, whenever possible, to determine the clinical significance of the gene sequence alteration.