Study of the molecular defects in glucose phosphate isomerase-deficient patients affected by chronic hemolytic anemia.

We have studied four unrelated Italian patients with chronic hemolytic anemia associated with glucose phosphate isomerase (GPI) deficiency. Using intronic primers, we were able to detect the gene alterations on the genomic DNA of the patients. Five different mutations were identified among the eight mutated alleles found: three missense mutations (301A,584T,1028G), one nonsense mutation (286T), and a four nucleotides deletion [Del 1473-IVS16(+2)]. All of these were new except for mutation 1028G, which was previously identified in a Japanese variant (GPI Narita). Two patients were homozygotes (301A/301A and 1028G/1028G), whereas the other two were compound heterozygotes sharing a common mutation [286T/584T and Del 1473-IVS16(+2)/584T]. The missense mutations were found to involve highly conserved amino acids, suggesting that these residues are crucial for the maintenance of the enzyme function. The mutation 286T results in a truncated protein of 95 amino acids in comparison with the 558 of the normal one. The four nucleotides deletion located at the junction of exon/intron 16(5'-TTGGTCGgtgagt-3') is the first GPI mutation affecting a splice site. Moreover one difference from the published sequence (473T-->G) was found in exon five in all of the eight alleles studied and in 30 normal subjects. Correlation was made between mutations, biochemical characteristics of the enzyme, and clinical course of the disease.