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Pathway Description
Tyrosinemia Type 2 (or Richner-Hanhart Syndrome)
Homo sapiens
Disease Pathway
Tyrosinemia II also known as Richner-Hanhart syndrome is an autosomal recessive disorder caused by a mutation in the TAT gene the encodes for tyrosine aminotransferase. A defect in this enzyme causes excess tyrosine to accumulate in the blood and urine, tyrosine crystals to form in the cornea, and increased excretion in the urine of 4-hydroxyphenylpyruvic acid, hydroxyphenyllactic acid, and p-hydroxyphenylacetic acid. Symptoms commonly appear in early childhood and include: mental retardation, photophobia (increased sensitivity to light), excessive tearing, eye redness and pain and skin lesions of the palms and soles. The patient is treated with restriction of dietary phenylalanine and tyrosine. Sometimes a tyrosine degradation inhibitor is also used to prevents the formation of fumarylacetoacetate from tyrosine. Trosinemia II is commonly misdiagnosed as herpes simplex keratitis.
References
Tyrosinemia Type 2 (or Richner-Hanhart Syndrome) References
Bienfang DC, Kuwabara T, Pueschel SM: The Richner-Hanhart syndrome: report of a case with associated tyrosinemia. Arch Ophthalmol. 1976 Jul;94(7):1133-7. doi: 10.1001/archopht.1976.03910040045009.
Pubmed: 180943
Chitayat D, Balbul A, Hani V, Mamer OA, Clow C, Scriver CR: Hereditary tyrosinaemia type II in a consanguineous Ashkenazi Jewish family: intrafamilial variation in phenotype; absence of parental phenotype effects on the fetus. J Inherit Metab Dis. 1992;15(2):198-203. doi: 10.1007/BF01799631.
Pubmed: 1356171
Hunziker N: Richner-Hanhart syndrome and tyrosinemia type II. Dermatologica. 1980;160(3):180-9. doi: 10.1159/000250493.
Pubmed: 6446465
al-Hemidan AI, al-Hazzaa SA: Richner-Hanhart syndrome (tyrosinemia type II). Case report and literature review. Ophthalmic Genet. 1995 Mar;16(1):21-6. doi: 10.3109/13816819509057850.
Pubmed: 7648039
Lehninger, A.L. Lehninger principles of biochemistry (4th ed.) (2005). New York: W.H Freeman.
Salway, J.G. Metabolism at a glance (3rd ed.) (2004). Alden, Mass.: Blackwell Pub.
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