HUMAN TRIOSEPHOSPHATE ISOMERASE DEFICIENCY RESULTING FROM MUTATION OFPHE-240

Triosephosphate isomerase (TPI; D-glyceraldehyde-3-phosphate ketolisom erase [E.C.5.3.1.1]) deficiency is an autosomal recessive disorder tha t typically results in chronic, nonspherocytic hemolytic anemia and in neuromuscular impairment. The molecular basis of this disease was ana lyzed for one Hungarian family and for two Australian families by loca lizing the defects in TPI cDNA and by determining how each defect affe cts TPI gene expression. The Hungarian family is noteworthy in having the first reported case of an individual, A. Jo., who harbors two defe ctive TPI alleles but who does not manifest neuromuscular disabilities . This family was characterized by two mutations that have never been described. One is a missense mutation within codon 240 (TTC [Phe]-->CT C [Leu]), which creates a thermolabile protein, as indicated by the re sults of enzyme activity assays using cell extracts. This substitution , which changes a phylogenetically conserved amino acid, may affect en zyme activity by disrupting intersubunit contacts or substrate binding , as deduced from enzyme structural studies. The other mutation has ye t to be localized but reduces the abundance of TPI mRNA 10-20-fold. Ea ch of the Australian families was characterized by a previously descri bed mutation within codon 104 (GAG [Glu]-->GAC [Asp]), which also resu lts in thermolabile protein.