All issues > Volume 45(2); 2002

Original Article

J Korean Pediatr Soc. 2002;45(2):183-191. Published online February 15, 2002.

Characterization of Bruton's Tyrosine Kinase Genetic Mutations in One Korean X-linked Agammaglobulinemia Family

Eun-Kyeong EK Jo¹, Chang-Hwa CH Song¹, Jeong-Kyu JK Park¹, Young-Jong YJ Baek², Hye-Young HY Rhu², Jae-Ho JH Lee², Tai-Ju TJ Hwang³, Hoon H Kook³

¹Department of Microbiology, College of Medicine, Chungnam National University, Taejon, Korea
²Department of Pediatrics, College of Medicine, Chungnam National University, Taejon, Korea
³Department of Pediatrics, Chonnam National University Medical School, Gwangju, Korea

Correspondence Hoon H Kook ,Email: hoonkook@chonnam.ac.kr

Abstract

Purpose
: X-linked agammaglobulinemia(XLA) is an immunodeficiency caused by abnormalities in Bruton's tyrosine kinase(Btk), and is characterized by a deficiency of peripheral blood B cells. We studied the cytoplasmic expression of Btk protein and analyzed the Btk gene in peripheral blood mononuclear cells from two siblings and one cousin with XLA, as well as additional family members.
Methods
: Btk protein expression was analyzed by flow cytometry. Isolation of the coding sequence of the Btk gene was performed by amplification using the reverse transcription-polymerase chain reaction(RT-PCR) technique. Sequence alterations were screened by the single-stranded conformation polymorphism(SSCP) method and characterized by standard sequencing protocols.
Results
: Cytoplasmic expression of Btk protein in monocytes was not detected in three patients with XLA. In addition, Btk protein analysis clearly showed cellular mosaicism in monocytes from four obligate carriers, findings further supported by SSCP. A single base pair mutation(T to C) in Btk-exon three, which encodes the PH domain, was identified in four XLA patients. A diagnostic sequencing analysis was established to detect heterozygotic pattern in 4 carrier females. Furthermore, we found significant clinical heterogeneity in individuals with the same gene mutation.
Conclusion
: The implicating genetic alteration provided valuable clues to the pathogenesis of XLA in Korea and the flow cytometric analysis was suggested as a useful tool for rapid detection of XLA patients and carriers. The present study has identified a genetic mutation in the Btk coding region and demonstrated heterogeneity in clinical manifestations among patients with the same mutation. A flow cytometric analysis was found to be informative in establishing a deficiency of Btk protein in both patients and carriers and is recommended as a frontline procedure in the molecular diagnosis and work-up of XLA.

Keywords :Bruton's tyrosine kinase, X-linked agammaglobulinemia, Direct sequencing, Flow cytometry, Carrier detection