Haemoglobin P-Nilotic containing a β-δ Chain

HAEMOGLOBIN P has been found amongst Nilotic populations of the then Belgian Congo, now called Zaire1,2 (Hb P Congo) and in the USA (Hb P Galveston)3. The abnormality in Hb P Galveston has been identified as β117 G19 His→Arg3, but the abnormality in Hb P Congo seems to be more complex and it has been suggested by Lehmann and Charlesworth4 that it is a “reversed Lepore” haemoglobin with a hybrid β-δ chain. In an extensive family study Dherte, Lehmann and Vandepitte1 found one man who had inherited Hbs A, S and P. His wife was a normal A/A homozygote and their children were all either A/S or A/P heterozygotes. Hybridization experiments demonstrated that the abnormality in the Hb P Congo was not in the α chain5. As the genes for the βA and βS chains are alleles at a single locus it is impossible for one individual to inherit Hbs A, S and P unless the gene for the non-α chain of Hb P is at a separate locus. A new genetic locus for a hybrid β-δ chain might be generated as shown in Fig. 1, by unequal but homologous crossing over of the genes for the δ and β chains6. One of the products of a crossing over would be a hybrid δ-β gene which would give rise to Hb Lepore. The other product would contain the genes for the δ and β chain and for a hybrid β-δ chain. The existence of homozygotes for Hb Lepore7 who make no Hb A or A2 suggests that the δ and β genes are in the order shown in Fig. 1. If a homozygote for the β-δ gene existed he would be expected to make Hb A and A2 as well.