A study of 23 patients with Hb H disease and their 82 relatives in 17 families showed that 2 types of this condition exist. One is associated with the presence of a small slow-moving component, which we tentatively called the X component and which was invariably present in one parent. Some siblings also had it. The other type was not associated with this component. Two patients without X component had a newborn with Bart’s haemoglobin without X component. None of the parents of 20 newborns with Hb Bart’s without the X component had the X component. It was present in only one parent of each of 2 newborns with Hb Bart’s and the X component. They are thought to represent Hb H disease in the newborn period. We suggest that at least 3 abnormal genes may lead to Hb H disease, which results when 2 of the 3 combine. Severity of clinical and haematological symptoms depends upon which abnormal gene is present and which 2 are involved in any particular combination.

In this paper we report this condition in 3 members of a Malay family. The unstable haemoglobin is structurally identical with Hb Koin first described by Pribilla (1962). We also report the results of enzyme studies of their red blood cells. MethodsHaematological examinations were made by standard methods. Haemolysates were prepared from washed red blood cells by the addition of 1 vol water and 04 to 0 5 vol toluene. Haemoglobin electrophoresis was carried out in starch gel with tris-EDTA boric acid buffer at pH 8-0 and 8-6 and discontinuous tris-boric acid buffer at pH 9-5; agar gel electrophoresis, with citric acid buffer pH 6-2, and cellulose-acetate electrophoresis with

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