Familial leukaemia: a study of 909 families.

A family survey was conducted among 909 patients with leukaemia of all types, with the purpose of establishing the incidence of further cases of leukaemia among relatives. Among a total of 41,807 relatives 8,349 were deceased, and the cause of death was objectively confirmed in 5,011. 72 patients had one or more relatives with leukaemia. First degree relatives with leukaemia were much more frequent in families of patients with chronic lymphocytic than in those of patients with chronic granulocytic leukaemia. The incidence of leukaemia among first degree relatives was established to be 2.8-3.0 times, among more distant relatives about 2.3 times, and overall about 2.5 times that expected. This excess is of the order of that observed in relatives of patients with certain solid tumors. Genetic factors may have accounted for much of the excess incidence in chronic lymphocytic and acute leukaemia, but there was little evidence for a genetic background in chronic granulocytic leukaemia. With the possible exception of one family with multiple cases, a simple Mendelian mechanism did not appear to be involved in the leukaemia families investigated. It appeared more likely that a polygenic mechanism led to a heightened susceptibility to the disease in these families.