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Reviewed August 2009
What is histidinemia?
Histidinemia is an inherited condition characterized by elevated blood levels of the amino acid histidine, a building block of most proteins. Histidinemia is caused by the shortage (deficiency) of the enzyme that breaks down histidine. Histidinemia typically causes no health problems, and most people with elevated histidine levels are unaware that they have this condition.
The combination of histidinemia and a medical complication during or soon after birth (such as a temporary lack of oxygen) might increase a person's chances of developing intellectual disability, behavioral problems, or learning disorders.
How common is histidinemia?
Estimates of the incidence of histidinemia vary widely, ranging between 1 in 8,600 to 1 in 90,000 people.
What genes are related to histidinemia?
Histidinemia is caused by mutations in the HAL gene, which provides instructions for making an enzyme called histidase. Histidase breaks down histidine to a molecule called urocanic acid. Histidase is active (expressed) primarily in the liver and the skin.
HAL gene mutations lead to the production of a histidase enzyme that cannot break down histidine, which results in elevated levels of histidine in the blood and urine. These increased levels of histidine do not appear to have any negative effects on the body.
Read more about the HAL gene.
How do people inherit histidinemia?
This condition is inherited in an autosomal recessive pattern, which means 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.
Where can I find information about diagnosis or management of histidinemia?
These resources address the diagnosis or management of histidinemia and may include treatment providers.
General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about histidinemia?
You may find the following resources about histidinemia helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
What other names do people use for histidinemia?
What if I still have specific questions about histidinemia?
Where can I find general information about genetic conditions?
The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful.
What glossary definitions help with understanding histidinemia?
amino acid ; ammonia ; autosomal ; autosomal recessive ; cell ; complication ; deficiency ; disability ; enzyme ; expressed ; gene ; His ; histidine ; incidence ; inherited ; molecule ; newborn screening ; oxygen ; recessive ; screening
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
See also Understanding Medical Terminology.
References (3 links)
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.