Tyrosinemia type II

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Tyrosinemia type II
L-tyrosine
Synonyms	Richner-Hanhart syndrome, Oculocutaneous tyrosinemia
Pronounce
Specialty	Medical genetics
Symptoms	Photophobia, eye pain, skin lesions, intellectual disability
Complications	N/A
Onset	Infancy or early childhood
Duration	Lifelong
Types	N/A
Causes	Genetic mutation in the TAT gene
Risks
Diagnosis	Blood test, urine test, genetic testing
Differential diagnosis	Tyrosinemia type I, Tyrosinemia type III, Alkaptonuria
Prevention
Treatment	Dietary restriction of tyrosine and phenylalanine
Medication
Prognosis	Generally good with treatment
Frequency	Rare
Deaths

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.

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.

See also

• 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