Valinemia is a very rare metabolic disorder. It is characterized by elevated levels of the amino acid valine in the blood and urine caused by a deficiency of the enzyme valine transaminase. This enzyme is needed in the breakdown (metabolism) of valine. Infants with valinemia usually have a lack of appetite, vomit frequently, and fail to thrive. Low muscle tone (hypotonia) and hyperactivity also occur.
The breakdown of valine involves at least seven stages and a deficiency of the appropriate enzyme at any of these stages leads to a disorder of varying severity and rarity.
Valinemia is usually present at birth. Symptoms in the newborn period include protein intolerance, metabolic acidosis, frequent vomiting, failure to thrive, and coma. The condition may become life-threatening. The levels of the amino acid valine in the blood and urine are elevated. Abnormally low muscle tone, excessive drowsiness, and/or hyperactivity can also occur.
Valinemia is a recessive genetic disorder. Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Valinemia is a rare disorder, occurring once in about 250,000 live births in the United States. It is present in affected infants at birth.
Diagnosis depends on the precise laboratory identification and measurement of metabolic products that accumulate in the blood and urine. Sophisticated chromatographic equipment is required to identify these metabolites.
A diet low in valine introduced during early infancy usually improves symptoms of valinemia, and lowers the valine concentrations in the blood to normal levels.
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McKusick VA, Ed. Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Entry Number; 277100: Last Edit Date; 8/22/1994.
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