Mutation analysis of Chinese patients with X-linked agammaglobulinemia

Abstract

AIM: Recently, mutation in human btk was shown to be the cause of X-linked agammaglobulinemia (XLA). Afflicted individuals are unduly susceptible to infection with high-grade encapsulated extracellular pyogenic pathogens. The hallmarks of the disease are low serum immunogloblin levels and a marked deficit in circulating B cells. Interestingly, although Btk is expressed in B cell and myeloid lineages, mutations appear to affect only B cell development. The development of B cell is arrested after the preliminary B cell stage implying btk serve as a signal molecule. Mutations of our patients with XLA are to be defined in order to provide genetic counselling for family. METHODS: A total of 11 Chinese XLA patients in 8 families were analysed for mutation of btk. Southern analysis was performed using full length btk cDNA probe. Exons of the entire btk were amplified from genomic DNA by using PCR. The primer were designed so that the DNA fragments ranged from 100-350 bp. These molecules were analysed by single strand conformational polymorphism (SSCP). Sequencing of abnormal bands from both genomic DNA and cDNA as template was done to define mutations. RESULTS: 3 mutations have been detected among 3 families so far. Patients I, II and III have mutations ATG=>ATT at codon 1 in exon 2 that lead to termination of the translation. Patient Vl has a single base deletion at codon 296 in exon 10 (1017A) and result in frame shift. Patient X has mutation CGT=>GGT at codon 641 in exon 18 resulting in amino acid change from arginine=>cystein . From Southern analysis, there was no any gross deletion or large rearrangement in the btk. CONCLUSION: From mutation analysis, we understand more about XLA at a molecular level and may be able to define the carriers in the families.