Tyrosinemia type II

A rare metabolic disorder affecting tyrosine metabolism

Tyrosinemia type II is a rare autosomal recessive metabolic disorder characterized by elevated levels of the amino acid tyrosine in the blood. It is one of the three types of tyrosinemia, the others being tyrosinemia type I and tyrosinemia type III.

Pathophysiology

Tyrosinemia type II is caused by a deficiency of the enzyme tyrosine aminotransferase (TAT), which is responsible for the conversion of tyrosine to p-hydroxyphenylpyruvate. This enzyme deficiency leads to the accumulation of tyrosine in the blood and tissues, resulting in various clinical manifestations.

Chemical structure of L-tyrosine

Clinical Features

The disorder typically presents in infancy or early childhood. The most common symptoms include:

• Keratitis, which can lead to eye pain and redness.
• Palmoplantar hyperkeratosis, characterized by thickening of the skin on the palms and soles.
• Intellectual disability or developmental delay in some cases.

Diagnosis

Diagnosis of tyrosinemia type II is based on clinical presentation, biochemical testing showing elevated tyrosine levels, and genetic testing confirming mutations in the TAT gene.

Treatment

Management of tyrosinemia type II involves dietary restriction of tyrosine and phenylalanine, as these amino acids are precursors in the metabolic pathway. This dietary management helps to reduce the levels of tyrosine in the blood and alleviate symptoms.

Genetics

Tyrosinemia type II is inherited in an autosomal recessive pattern, meaning that both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Epidemiology

Tyrosinemia type II is a rare disorder, with a higher prevalence in certain populations due to founder effects. The exact incidence is not well established but is significantly lower than that of tyrosinemia type I.

Related pages

• Tyrosinemia type I
• Tyrosinemia type III
• Inborn errors of metabolism

References

• Grompe, M. (2001). "The pathophysiology and treatment of hereditary tyrosinemia type 1." Seminars in Liver Disease, 21(4), 563-571.
• Phaneuf, D., & Lambert, M. (2001). "Tyrosinemia type II." Orphanet Journal of Rare Diseases, 6, 73.

Metabolic pathway of phenylalanine and tyrosine