Haemoglobin J Tongariki is associated with α thalassaemia

Abstract

GENETIC evidence suggests that the haemoglobin (Hb) α chain genes are duplicated in at least some human populations, as a number of individuals are known to have two different α chain variants in addition to HbA (ref. 1). Furthermore the presence of two α chain genes per haploid genome has been demonstrated in a few cases using direct measurement by DNA hybridisation^2,3. However, this may not be true of all racial groups, particularly the Melanesian populations in which HbJ Tongariki is found. Abramson et al.⁴ and Beaven et al.⁵ described five individuals who were apparently homozygous for this α chain variant, none of whom had any detectable HbA. α Thalassaemia was discounted on haematological grounds, and it was concluded that some, if not all, Melanesians have only one α chain locus. However, as recent studies have shown that two of the common forms of α thalassaemia are due to α gene deletion^6–8, the disease must be quite rigorously excluded before the number of α gene loci can be deduced solely on the basis of genetic evidence. We have studied again the family described by Beaven et al., and other unrelated individuals, all of whom live on Karkar Island, off the northern coast of Papua New Guinea. By determination of α/β mRNA ratios in these individuals we have obtained evidence which strongly suggests that they are in fact homozygous for an α thalassaemia gene.