Alpha thalassaemia in American blacks: a study of a family with five cases of haemoglobin H disease.

Five cases of HbH disease were discovered in a large family of American Blacks. Anaemia was mild with PCV ranging from 0.275 to 0.405. The amount of HbH was 2--6%. Studies of haemoglobin synthesis in peripheral blood reticulocytes demonstrated marked deficits in alpha globin production with an average alpha/beta ratio of 0.31 (range 0.22--0.36). Eighteen additional family members had evidence of thalassaemia trait and were provisionally classified as either alpha-thal-1 (average MCV 65.2 fl; range 59--70) or alpha-thal-2 (average MCV 79.6 fl; range 74--88). A subject with altha-thal-1 trait had an alpha/beta ratio of 0.56; the average for five cases of alpha-thal-2 was 0.73. One other family member was thought to be homozygous for alpha-thal-2 trait and exhibited an MCV of 65 fl with an alpha/beta ratio of 0.5. These data reconfirm that in Blacks with alpha thalassaemia the proportion of HbH is lower and the severity of anaemia is less than in certain other racial groups, e.g. Southeast Asians. However, the degree of hypochromia and microcytosis and the imbalance in alpha and beta globin synthesis appear to be similar in Blacks and other races. These results suggest that the milder clinical course of HbH disease in Blacks is not a result of greater alpha globin production in that population of thalassaemics.