Mutation analysis of the Bruton's tyrosine kinase gene in X-linked agammaglobulinemia: identification of a mutation which affects the same codon as is altered in immunodeficient xid mice.
We investigated BTK gene expression in an XLA/GHD patient from the family originally described by Northern analysis, cDNA sequencing, and Western analysis of protein production using mAb to BTK.
The phenotype of XLA can be variable, with some individuals having a less severe immunophenotype, although in most cases this cannot be correlated with the Btk mutation or expression of Btk protein.
A single XLA patient with torsion dystonia and cosegregating X-linked deafness has been found with a deletion in the 3' part of BTK extending centromerically into the flanking expressed sequence DXS1274E.
Seven individuals with the diagnosis of X-linked agammaglobulinemia were analyzed for mutations in Bruton tyrosine kinase (Btk) gene at both the cDNA transcript and genomic DNA levels.
Newborn screening for kappa-deleting-recombination-excision circles (KRECs) reliably identifies classical X-linked agammaglobulinaemia (XLA) patients with profound B-cell lymphopenia at birth but has not been evaluated in patients with residual BTK function.
Although neutropenia was not associated with any specific mutation in Btk, most of the alterations in this gene in the patients with XLA and neutropenia resulted in the absence of Btk protein or in amino acid substitutions in sites thought to be critical to Btk function.
The molecular study with DNA sequencing of the patient showed a point mutation in complementary DNA 1630 A>G(p.R544G) in the BTK gene, indicating that the patient has XLA.
In pursuit of definitive therapy for XLA, we tested ex vivo gene therapy using a lentiviral vector (LV) containing the immunoglobulin enhancer (Emu) and Igbeta (B29) minimal promoter to drive B lineage-specific human Btk expression in Btk/Tec(-/-) mice, a strain that reproduces the features of human XLA.