Identification of a Novel Mutation of Bruton's Tyrosine Kinase(BTK)Gene in a X-linked Agammaglobulinemia(XLA) Family

ABSTRACT

X-linked agammaglobulinemia(XLA) is a heritable humoral immunodeficiency disease characterized by inefficient expansion of pre-B cells into later B cell stages or incomplete differentiation of B cell precursors to pre-B cells. The gene mutated in XLA was identified as a cytoplasmic tyrosine kinase, named Bruton's tyrosine kinase(BTK). In this report we investigated the characteristics of immune cells, the patterns of intracellular BTK protein expression by flow cytometry, and the genetic abnormality by direct sequencing in one Korean XLA family. Finally, we found that the serum immunoglobulins and the number of peripheral B cells were extremly low in the patient and his brother. The histogram of intracellular BTK staining in the patient and his brother showed typical case of XLA, whereas that of their mother showed a carrier pattern. We also identified a novel point mutation in the first intron of the BTK gene in the patient and his brother. The genomic DNA sequencing of mother and sister showed a G/A heterozygote pattern. These results will provide valuable clues to the pathogenesis of XLA, and suggest an approach useful for carrier detection.