BTK and Bruton-type agammaglobulinemia: This variant has been reported in patients with XLA previously [87,88], but researchers studying BTK variant effects on protein have drawn attention to dissimilarities between this variant and other pathogenic BTK variants—while the majority of disease-causing BTK variants are missense changes in structurally important residues of the tyrosine kinase domain, L652P is not a well-conserved location and the residue is exposed in the assembled protein structure [89,90].