[Familial leukemia (author's transl)].

Among 2966 acute leukemia, 26 familial cases were reported. Leukemia occured mainly in the first relative individuals and particularly in the sibship. The relative risk for a sib of leukemic patient is four time more than for random people. Leukemia was often similar among patients of the same family and the onsets of the disease occured approximatly at the same age whatever the time between the dates of diagnosis. Twins with leukemia were often monozygotous. Relative risk of leukemia among twins, decreases according to the age: the probability of leukemia for a twin is: (a) 100 p. cent if the other twin is leukemic before 1 year old; (b) 15 p. cent between 1 to 4 years old and (c) similar to other sib after 4 years old. Among chronic leukemias, only chronic lymphocytic leukemia seems to have a genetic background for susceptibility. Some familial diseases (congenital aplastic anemia, Bloom's disease, Ataxia telangiectasia) or congenital diseases (Down's syndrome) increase the risk of leukemia.