TPI deficiency: A case report and review of the literature.

Triosephosphate isomerase (TPI) is a ubiquitously expressed enzyme encoded by the TPI1 gene. It catalyzes the interconversion of the triose phosphate isomers dihydroxyacetone phosphate and D-glyceraldehyde 3-phosphate in the fifth step of glycolysis. TPI deficiency (TPI Df; MIM# 615512) is an autosomal recessive disorder due to biallelic pathogenic variants in TPI1. In keeping with other glycolytic enzymopathies, severe hemolytic anemia is a common finding. Additionally, many individuals with TPI Df develop neuromuscular symptoms, which is unusual for a glycolytic enzymopathy. There appears to be a genotype-phenotype correlation between a TPI1 p.Glu105Asp/null genotype and a severe life-limiting neuromuscular phenotype. Tpi1-deficient mice with a p.Glu105Asp/null genotype recapitulate the life-limiting neuromuscular phenotype seen in humans, but the exact pathomechanism remains unclear. Here we describe a 2-month-old male proband who presented with failure to thrive, respiratory failure, seizures, and severe hemolytic anemia, who passed away at 3 months of age. Trio whole genome sequencing showed compound heterozygous variants with the common p.Glu105Asp variant in trans to a newly described likely pathogenic splice site c.324 + 1G > C variant, predicted to cause nonsense mediated decay. Here we review our case as well as the literature to hypothesize a mechanism by which TPI Df due to a p.Glu105Asp/null genotype causes severe disease. Given the overall fatal nature of this condition, novel therapeutic approaches are urgently needed. Currently, treatments are experimental. Ketogenic diet and triheptanoin were effective in treating seizures in a TPI mutant Drosophila, known as TPI, although clinical data in humans is lacking. Additionally, bone marrow transplant has been shown to improve the hematologic phenotype in mice and has been done in an isolated number of patients. While there are no proven therapies available at this time, we hope this review will lead the discussion to consider future therapeutic options.