Japanese B cell chronic lymphocytic leukaemia: a cytogenetic and molecular biological study

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Abstract
Summary. Clinical, cytogenetic, and molecular genetic studies were performed to clarify the pathophysiology of Japanese B cell chronic lymphocytic leukaemia (B‐CLL), since the incidence of B‐CLL in Japan is significantly lower than in western countries. The clinical and laboratory features of 55 Japanese patients with B‐CLL in this study did not differ from those of Americans or Europeans with B‐CLL. In the chromosome analyses, suitable metaphases with good band quality were obtained from 48 patients (87.2%), of whom 22 patients (45.8%) showed clonal chromosome aberrations and 14 (29.2%) had non‐clonal aberrations. Trisomy 12 and abnormalities of 14q and 13q were found in four (18.2%), two (9.1%) and six patients (27.2%). respectively. There were no particular chromosome abnormalities or specific breakpoints in Japanese B‐CLL. However, complex karyotype was found in higher incidence than in western countries. In the Southern blot analyses, rearranged band patterns were observed in the major breakpoint region (mbr) of the bcl‐2 gene in one case, in the 5′‐breakpoint region (5′‐bcl‐2) in two, and bcl‐3 in one. Of the two patients with 5′‐bcl‐2 rearrangements, one had a normal karyotype and the other had t(2:18)(p12:q21). The incidence of rearrangements of the bcl‐1, bcl‐2 and bcl‐3 genes in Japanese B‐CLL was similar to that in western countries. These findings suggest that the biological characteristics of B‐CLL in Japan are almost the same as those in western countries, although the incidence of B‐CLL in Japan is quite different: this may be related to racial differences, which seem to be an important factor in the development of B‐CLL.