A family predisposition to adult T-cell leukemia.

We report here the rare case of a family predisposed to adult T-cell leukemia (ATL). Six of seven siblings developed ATL with ages of onset of 77, 48, 60, 64, 72, and 62 years old. Although virological tests for human T-lymphotropic virus type 1 were unavailable for two of the six patients, all were diagnosed with ATL based on their clinical, hematological, and histopathological features. Two of the six patients were tested for HLA haplotypes using fresh blood samples, and both were carriers of the HLA-A*26 allele known in the southern Japanese population to be susceptible to ATL. This series of genetic traits may help explain the familial predisposition to ATL.