We have identified a 52-year-old woman and her 27-year-old daughter with macrocytosis, normal haemoglobin and mean corpuscular haemoglobin concentration, Macrocytosis could be demonstrated from the age of 40 and 25 respectively. All blood tests were normal including vitamin B-12 and folic acid. Bone marrow investigation showed rare macroblasts without other abnormalities. Endoscopy of the upper gastrointestinal tract and ultrasonography of the abdomen were normal, Thus, persistent macrocytosis was present without evidence of diseases that might account for it, In these subjects, macrocytosis is likely to be related to the presence of a genetic defect.
