Triosephosphate isomerase deficiency

Triosephosphate isomerase deficiency
Synonyms	Triose phosphate-isomerase deficiency, TPI deficiency
Pronounce
Field	Hematology, Neurology, Genetics
Symptoms	Hemolytic anemia, neuropathy, developmental delay, cardiomyopathy, recurrent infections
Complications	Respiratory failure, cardiac arrest, early death
Onset	Infancy or early childhood
Duration	Lifelong
Types
Causes	Mutations in the TPI1 gene
Risks	Family history of the condition
Diagnosis	Genetic testing, enzyme assay, blood smear, clinical presentation
Differential diagnosis	Pyruvate kinase deficiency, glucose-6-phosphate dehydrogenase deficiency, metabolic disorders
Prevention	Genetic counseling
Treatment	Supportive care
Medication	Transfusion, antibiotics, experimental enzyme replacement therapy
Prognosis	Poor (most cases fatal in early life)
Frequency	Extremely rare (<100 known cases worldwide)
Deaths	High mortality rate in early childhood

Triosephosphate isomerase deficiency (TPI deficiency) is an extremely rare autosomal recessive disorder that affects glycolysis, the metabolic pathway responsible for breaking down glucose into energy. The condition results from mutations in the TPI1 gene, leading to deficiency of the triosephosphate isomerase enzyme. It is characterized by hemolytic anemia, severe neurological impairment, recurrent infections, and often early childhood death.

Pathophysiology

TPI deficiency is classified as a glycolytic enzymopathy, meaning it involves a deficiency of an enzyme in the glycolytic pathway. The triosephosphate isomerase enzyme catalyzes the reversible conversion of dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P), which are intermediates in glycolysis.

In individuals with TPI deficiency, the enzyme's activity is markedly reduced, leading to:

• Accumulation of DHAP
• Decreased cellular energy production
• Increased vulnerability of red blood cells to oxidative stress and premature destruction (hemolysis)
• Impaired neuromuscular and immune system function

Genetics

TPI deficiency is inherited in an autosomal recessive manner. Affected individuals inherit two defective copies of the TPI1 gene (located on chromosome 12p13). To date, at least thirteen mutations have been identified. These mutations result in either:

• Disrupted protein folding
• Impaired dimerization of the enzyme
• Accelerated degradation of the TPI protein

Carriers (heterozygotes) typically do not show clinical symptoms, even though they may have lower enzyme activity. It has been suggested that there may be a heterozygote advantage in some populations.

Clinical Presentation

Symptoms typically begin in infancy or early childhood and may include:

• Chronic hemolytic anemia
• Muscle weakness and hypotonia
• Developmental delay
• Seizures
• Recurrent infections due to immune deficiency
• Cardiomyopathy
• Respiratory failure
• Feeding difficulties
• Failure to thrive

The disease is progressive and often fatal during the first decade of life.

Diagnosis

Diagnosis is based on:

• Clinical signs of hemolytic anemia and neurological dysfunction
• Blood smear showing abnormal erythrocytes
• Enzyme assay showing low or absent TPI activity in red blood cells
• Genetic testing confirming mutations in TPI1

Differential Diagnosis

Conditions with overlapping symptoms may include:

• Pyruvate kinase deficiency
• Glucose-6-phosphate dehydrogenase deficiency
• Congenital metabolic disorders
• Neuromuscular diseases

Treatment

There is currently no cure for TPI deficiency. Management is supportive and may include:

• Blood transfusions for severe anemia
• Antibiotics for infections
• Physical therapy and supportive care
• Respiratory support as needed
• Experimental therapies such as enzyme replacement therapy or gene therapy are under investigation

Prognosis

Prognosis is generally poor. Many affected children die before the age of 5–10 years due to complications such as respiratory failure, severe anemia, or infections. However, disease severity can vary depending on the specific mutation(s) involved.

Epidemiology

TPI deficiency is exceptionally rare, with fewer than 100 documented cases worldwide. It affects both males and females and occurs in all ethnic groups.

See also

• Glycolysis
• Enzymopathy
• Hemolytic anemia
• Congenital metabolic disorder
• Autosomal recessive inheritance

External links

• OMIM entry on TPI deficiency
• NIH Genetic and Rare Diseases Information Center
• Genetic Testing Registry entry

NIH genetic and rare disease info

• NIH info on Triosephosphate isomerase deficiency

Triosephosphate isomerase deficiency is a rare disease.