Incidence of haemoglobin Thai: a re‐examination of the genetics of α‐thalassaemic diseases

Haemoglobin (Hb) H disease is a mild to severe a-thalassaemic disease, characterized by the haemoglobin types of A + H and intra-erythrocytic inclusion bodies. The latter are aggregated masses of Hb H (/I4). This disease has been reported from many parts of the world, but is especially common among the Thai and the Chinese. Over 400 patients have been examined by us, not including more cases in the Department of Paediatrics of this hospital. The genetics of Hb H disease is peculiar, Hb H being not detectable in either parent in the majority of cases. It has been suggested (Wasi, Na-Nakorn & Suingdumrong, 1964; Huehns, 1965) that this disease results from double heterozygosity between a severe a-thalassaemia gene (a-thal,) and a milder allele (a-thal,). a-thal, leads to a complete, while a-thal, to a partial, suppression of a-chain synthesis. Homozygosity for a-thal, results in Hb Bart's hydrops foetalis in which no Hb A is synthesized (Weatherall, Clegg & Wong, 1970; Todd et al. 1970). Further evidence (Na-Nakorn et al. 1969; Na-Nakorn & Wasi, 1970) supports the hypothesis of a-thal, and a-thal,. A haemoglobin, slower than Hb A, in starch-gel electrophoresis in alkaline pH, in association with a-thalassaemic diseases, was first reported from this laboratory in 1967 (Wasi et al. 1967) and again in 1968 (Wasi et al. 1969). This was found by Dr E. R. Huehns to be an a-chain variant, and has been named Hb Thai (Wasi, 1970b). Hb Thai constitutes only 1-2 % or less of the total haemoglobin. Thus it often escapes detection. The reason for its presence in such a small amount is yet to be shown, but it is very likely that this is due to decreased synthesis. Hb Thai gene, with almost complete suppression of a-chain synthesis, thus would have an a-thalassaemia-like effect. Double heterozygosity between Hb Thai gene and an a-thalassaemia gene should lead to a Hb H disease with the presence of a small amount of Hb Thai. The prevalence of Hb Thai among a-thalassaemic diseases has never been reported before. This should be very important in understanding the genetics of a-thalassaemia. We wish to report the incidence of Hb Thai among patients with Hb H disease. b