sentences:  A marked decrease in TPI activity and an accumulation of dihydroxyacetone phosphate have been detected in erythrocyte extracts of homozygous (two identical mutant alleles) and compound heterozygous (two different mutant alleles) TPI deficiency patients.Heterozygous individuals are clinically unaffected, even if their residual TPI activity is reduced.Recent work suggests that not a direct inactivation, but an alteration in TPI dimerization might underlie the pathology.