Congenital enzymopenic methaemoglobinaemia. Clinical and biochemical study of a family with three homozygotes.

Three brothers with congenital recessive methaemoglobinaemia without mental retardation were found to be homozygous for NADH diaphorase deficiency. Twelve family members were heterozygous. One of the probands had marked digital clubbing, an unusual feature in this disease. In the probands, the red-cell NADH diaphorase was very low and unstable, whereas in the leucocytes this enzyme was present at a normal level. Isoelectric focusing of haemoglobin in the three probands showed that the alpha-chain was preferentially oxidized spontaneously. This confirms the greater oxidizability of this chain, as already described on isolated chains.