Hb Belfast [beta15(A12)Trp-->Arg]: definition of the clinical and hematological phenotype.

We report the sixth occurrence of Hb Belfast [beta15(A12)Trp-->Arg], a mild, unstable beta chain variant, in a large family wherein nine subjects were affected. DNA analysis showed a TUG-->AGG mutation at codon 15 of the beta-globin gene, confirming a Trp-->Arg amino acid substitution. The oxygen affinity of the isolated variant was increased. The clinical phenotype is silent or very mild, the only clinical finding being an intermittent moderate jaundice.