The mutation is a T-to-A transversion at codon 192 in exon 6. This is predicted to alter a leucine to a glycine in the H6 alpha-helix on the outer surface of the protein. This mutation is identical to Tpim-1Neu, but arose independently. TPI1 activity in heterozygotes is 50% that of wild-type in blood; and also reduced in liver, lung, spleen, kidney, brain, heart and muscle.