Acute leukaemia in siblings.

Unequivocal lymphoblastic leukaemia in a 4-year-old boy was followed 3 years later by equally unequivocal myeloblastic leukaemia in his 20-year-old brother. The boy achieved complete remission and remains well more than 6 years later whereas his brother failed to respond to treatment and died after 5 months. The parents and 3 remaining siblings showed no recognized features suggesting a constitutional predisposition to leukaemia despite thorough investigation.