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Tyrosinemia type III is a rare disorder caused by a deficiency of the enzyme 
4-hydroxyphenylpyruvate dioxygenase
4-Hydroxyphenylpyruvate dioxygenase (HPPD), also known as α-ketoisocaproate dioxygenase (KIC dioxygenase), is an Fe(II)-containing non-heme oxygenase that catalyzes the second reaction in the catabolism of tyrosine - the conversion of 4-hydro ...
(), encoded by the gene ''HPD''. This enzyme is abundant in the liver, and smaller amounts are found in the kidneys. It is one of a series of enzymes needed to break down tyrosine. Specifically, 4-hydroxyphenylpyruvate dioxygenase converts a tyrosine byproduct called 4-hydroxyphenylpyruvate
4-Hydroxyphenylpyruvic acid (4-HPPA) is an intermediate in the metabolism of the amino acid phenylalanine. The aromatic side chain of phenylalanine is hydroxylated by the enzyme phenylalanine hydroxylase to form tyrosine. The conversion from tyr ...
to homogentisic acid. Characteristic features of type III tyrosinemia include mild mental retardation, seizure
An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with los ...
s, and periodic loss of balance and coordination (intermittent ataxia
Intermittency is a behavior of dynamical systems: regular alternation of phases of apparently periodic and chaotic dynamics.
Intermittent or intermittency may also refer to:
* Intermittent river or stream, the one that ceases to flow every year or ...
). Type III tyrosinemia is very rare; only a few cases have been reported.
References
External links
{{Amino acid metabolic pathology Amino acid metabolism disorders Autosomal recessive disorders