Description, Causes and Risk Factors:
A rare, autosomal-recessive disease causing loss of excessive biotin; clinical manifestations may be absent, but extreme manifestations include seizures, alopecia, dermatitis, hypotonia, optic atrophy, ataxia, developmental delay, hearing deficits, and occasionally immunodeficiency; trait has a prevalence of 1 in 60,000.
Biotinidase is an enzyme that is essential for the recycling of the vitamin biotin. Biotin, in turn, is important as an enzyme cofactor. Free biotin is needed to activate carboxylase enzymes by binding at a specific site. Carboxylases are important in the production of certain fats and carbohydrates and for the breakdown of proteins. This process is blocked if an individual has biotinidase deficiency.
Biotinidase deficiency is caused by mutations in the BTD gene (3p25) resulting in reduced or absent BTD activity. This enzyme recycles free, non-protein bound, biotin which is required for multiple biotin-dependent metabolic processes. There are more than 150 known mutations of the BTD gene that cause biotinidase deficiency.
Biotinidase deficiency is inherited as an autosomal-recessive disease. Parents of a child with biotinidase deficiency are assumed to be carriers for the disease and have a 1 in 4 (25%) chance, in each pregnancy, of having another child with this condition. Prenatal testing for biotinidase deficiency can be done as early as 15-16 weeks of pregnancy. Genetic counselling to discuss the benefits of prenatal testing options in more detail is recommended.
Unaffected siblings of a child with biotinidase deficiency have a 2/3 chance of being carriers. Carriers are healthy and do not have symptoms of biotinidase deficiency. The prognosis for individuals diagnosed with biotinidase deficiency is very good, provided they are treated before symptoms occur and are compliant with biotin therapy.
Optic nerve atrophy.
Metabolic acidosis which even leads to coma and death.
Specific tests include the following:Serum ammonia, urine organic acids, plasma amino acids, urine ketones, blood gas, serum chemistries, biotinidase, carnitine, and acylcarnitine profiles.
MRI is the Neuroimaging study of choice for the evaluation of a child with a possible inborn error of metabolism. Children with biotinidase deficiency may demonstrate cerebral edema, low attenuation of white matter signal, cerebral atrophy, and compensatory ventricular enlargement.Magnetic resonance spectroscopy also helps determine the functional metabolism of the brain. Some facilities have access to these techniques and using them may help to delineate the nature of the brain disorder in vivo.
Positron emission tomography is used in an experimental setting to demonstrate the change in cerebral metabolic activity before and after biotin therapy.CT scan may demonstrate bilateral basal ganglia calcifications that may not be as readily demonstrated on MRI.
Other cases are diagnosed by clinical signs and symptoms and confirmed by demonstration of deficient serum BTD activity. Molecular mutation analysis of the BTD gene is also possible.
Supplementation with oral biotin in the free, non-protein bound, form is the primary treatment and improves symptoms in symptomatic patients, and prevents symptoms in those identified by newborn screening or before symptoms have developed. Once some features, such as optic atrophy, hearing loss, or developmental delay develop, they may not be reversible with biotin treatment. Treatment with biotin should be maintained lifelong. There are no known, serious adverse effects of biotin therapy. Patients and their families should be warned about the importance of treatment compliance. Periodic ophthalmological, neurological and metabolic evaluations are recommended. Raw eggs should be avoided because of their avidin content (biotin-binding substance), but cooking inactivates the binding effect of avidin.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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