Molecular basis of chronic non-spherocytic haemolytic anaemia: a new G6PD variant (393 Arg----His) with abnormal KmG6P and marked in vivo instability.

Summary. More than 80 genetic variants of glucose-6-phosphate dehydrogenase (G6PD) are associated with chronic non-spherocytic haemolytic anaemia (CNSHA). In order to help clarify the molecular basis of this association, we have carried out a detailed biochemical and genetic characterization of two G6PD deficient brothers affected by CNSHA. The G6PD from the two patients has altered electrophoretic mobility, abnormally elevated Michaelis constant (Km) for G6P, and extreme instability in vivo and in vitro. By comparison with published information we found that this is a new G6PD variant which we have designated G6PD Portici. The entire coding region of the gene has been sequenced, and a single point mutation, a GA transition, was found at position 1178 in exon X, causing a substitution of histidine for arginine at residue 393 in the polypeptide chain. By polymerase chain reaction (PCR) amplification followed by diagnostic restriction enzyme analysis and allele-specific oligonucleotide hybridization we have demonstrated the inheritance of this mutation in the patient's family. Our results support the notion of a causative link between this mutation in the G6PD gene and CNSHA. Our data, in combination with previous data in the literature, suggest that the three-dimensional structure of G6PD is such as to cause interaction in the binding of its two substrates, G6P and NADP.