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Biotinidase Deficiency |
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Condition: Biotinidase Deficiency
"Biotinidase Deficiency (not enough of the enzyme biotinidase) leads to seizures, skin infections, hair loss, hearing and vision loss, mental retardation, and possibly coma and death. Giving the baby extra biotin (a vitamin) avoids these problems" - Vermont Newborn Screening
Technical information from the Mountain States Genetic Network:
Biotinidase is an enzyme that liberates biotin, an essential cofactor, from a bound form so that it can be used by the body. Deficiency of the enzyme in serum results in improper functioning of several other enzyme systems, leading to irreversible neurological damage. This autosomal recessive disorder has an estimated incidence of 1:60,000 births.
Metabolic Pathway: Biotinidase Deficiency
Clinical Features
The symptoms of biotinidase deficiency are variable with respect to age of onset, frequency, and severity. Signs and symptoms generally appear in infancy or early childhood and may include seizures, skin rash, hair loss, hypotonia, ataxia, hearing loss, optic nerve atrophy, developmental delay, and metabolic acidosis which can result in coma and death. Clinical symptoms have been reported in the second month in untreated babies. Individuals with partial deficiency (the variant form) may also be at risk for development of symptoms and family studies are indicated when an affected newborn is identified.
Laboratory Tests
Detection of enzyme activity is usually performed by a qualitative colorimetric assay. In the presence of the enzyme a color change occurs.
Treatment
The acute symptoms of biotinidase deficiency will completely disappear with administration of pharmacological doses of biotin, usually 10 mg per day. If given early enough in an infant's life, the prognosis for normal growth and development is good. If children are not detected until irreversible neurological damage has occurred, treatment with biotin will prevent further damage but will not reverse the damage already done.
Screening Practice Considerations
Detection of the deficiency does not depend on timing or type of feeding because it is a serum enzyme assay. It should therefore be detected on the first specimen unless the infant has been transfused with whole blood or with plasma or serum; always obtain a newborn screening specimen prior to a transfusion.
The enzyme is prone to damage if the sample is delayed in the mail or exposed to high temperatures.
Prompt confirmatory testing is required even if there is evidence to suggest that one of the situations associated with false positive screens is present (these include early specimen collection, prematurity, heat-damaged specimen, hyperalimentation, or antibiotic therapy). The presence of any of these does not exclude the possibility of disease.
The diagnostic test for biotinidase deficiency is a quantitative assay of enzyme activity in frozen serum, performed by a limited number of reference laboratories. Diagnostic testing should be coordinated by a metabolic center.
The purpose of newborn screening is to identify infants at risk and in need of more definitive testing.
As with any laboratory test, both false negative and false positive results are possible.
Screening test results are insufficient information on which to base diagnoses or treatment.
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