The haematological puzzle of Hb J Cape Town is partly solved.

Molecular studies have shown that the mutation giving rise to Hb J Cape Town (alpha 92 arg----gln) is situated on a chromosome from which the other alpha-globin gene has been deleted. The -alpha 3.7 deletion has resulted from crossing-over within segment I of the Z region of homology. There appears to be an unusually high proportion of the variant haemoglobin in heterozygotes which cannot be explained by gene dosage alone.