Third case of chronic lymphocytic leukaemia in a carrier of the inherited Ch1 chromosome.

Chronic lymphocytic leukaemia has developed in three siblings who are all carriers of the abnormal Ch(1) chromosome. (3)H-thymidine autoradiography showed Ch(1) to be a G(2) autosome, from which the short arm is absent, and not G(1), which is trisomic in Down's syndrome and which is believed to form the abnormal Ph(1) chromosome. Ch(1) is not of general significance in the aetiology of chronic lymphocytic leukaemia, but it must be considered as a possible predisposing factor to leukaemia in the present family.