The HPD gene provides instructions for making an enzyme called 4-hydroxyphenylpyruvate dioxygenase. This enzyme is abundant in the liver, and smaller amounts are found in the kidneys. It is second in a series of five enzymes that work to break down the amino acid tyrosine, a protein building block found in many foods. Specifically, 4-hydroxyphenylpyruvate dioxygenase converts a tyrosine byproduct called 4-hydroxyphenylpyruvate to homogentisic acid. Continuing the process, homogentisic acid is further broken down and ultimately smaller molecules are produced that are either excreted by the kidneys or used to produce energy or make other substances in the body.
Health Conditions Related to Genetic Changes
Researchers have identified at least six HPD gene mutations that cause tyrosinemia type III. This condition is characterized by neurological problems such as intellectual disability, seizures, and periodic loss of balance and coordination (intermittent ataxia). Some of the mutations that cause this condition change single amino acids in the 4-hydroxyphenylpyruvate dioxygenase enzyme. Other mutations lead to the production of an unusually small enzyme. As a result of these mutations, the activity of the 4-hydroxyphenylpyruvate dioxygenase enzyme is unusually low or absent. As a result, the enzyme cannot perform its role in the breakdown of tyrosine, so 4-hydroxyphenylpyruvate is converted to toxic compounds instead of homogentisic acid. As these toxic compounds builds up in cells, they can impair function and eventually cause cell death. Cells in the nervous system are particularly sensitive to this toxic accumulation. Nerve cell damage and death likely lead to the characteristic features of tyrosinemia type III.More About This Health Condition
At least two HPD gene mutations have been found to cause a rare condition called hawkinsinuria. In infants, this condition is characterized by a failure to gain weight and grow at the expected rate (failure to thrive) and abnormally high acid levels in the blood (acidosis). The HPD gene mutations that cause hawkinsinuria result in decreased enzyme activity so that 4-hydroxyphenylpyruvate is not efficiently converted to homogentisic acid. Instead, some 4-hydroxyphenylpyruvate forms an unusual sulfur-containing amino acid called hawkinsin. It remains unclear how the production of hawkinsin leads to the features of hawkinsinuria.
Other Names for This Gene
- P-hydroxyphenylpyruvate hydroxylase
- P-hydroxyphenylpyruvate oxidase
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
- Aarenstrup L, Falch AM, Jakobsen KK, Neve S, Henriksen L LØ, Tommerup N, Leffers H, Kristiansen K. Expression and post-translational modification of human 4-hydroxy-phenylpyruvate dioxygenase. Cell Biol Int. 2002;26(7):615-25. Citation on PubMed
- Brownlee JM, Heinz B, Bates J, Moran GR. Product analysis and inhibition studies of a causative Asn to Ser variant of 4-hydroxyphenylpyruvate dioxygenase suggest a simple route to the treatment of Hawkinsinuria. Biochemistry. 2010 Aug 24;49(33):7218-26. doi: 10.1021/bi1008112. Citation on PubMed
- Ellaway CJ, Holme E, Standing S, Preece MA, Green A, Ploechl E, Ugarte M, Trefz FK, Leonard JV. Outcome of tyrosinaemia type III. J Inherit Metab Dis. 2001 Dec;24(8):824-32. Citation on PubMed
- Heylen E, Scherer G, Vincent MF, Marie S, Fischer J, Nassogne MC. Tyrosinemia Type III detected via neonatal screening: management and outcome. Mol Genet Metab. 2012 Nov;107(3):605-7. doi: 10.1016/j.ymgme.2012.09.002. Epub 2012 Sep 7. Citation on PubMed
- Rüetschi U, Cerone R, Pérez-Cerda C, Schiaffino MC, Standing S, Ugarte M, Holme E. Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III. Hum Genet. 2000 Jun;106(6):654-62. Citation on PubMed
- Tomoeda K, Awata H, Matsuura T, Matsuda I, Ploechl E, Milovac T, Boneh A, Scott CR, Danks DM, Endo F. Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria. Mol Genet Metab. 2000 Nov;71(3):506-10. Citation on PubMed