Congenital deficiency of biotinidase is a rare congenital metabolic disorder that most often occurs in newborns and young children. Since the activity of the enzyme in the nervous tissue is low, it is the most sensitive and vulnerable, which is manifested primarily by muscle hypotension, convulsions, ataxia, and dermal disorders. Clinically, there are two forms of biotinidase deficiency, which are determined by the residual activity of the enzyme: early (deep deficiency), late (partial). The leading laboratory tests are the detection of metabolic acidosis in the patient, the study of urine for organic acids, low enzyme activity, hyperammonemia, and the detection of mutations in the sequencing of the BTD gene. The features of neurological disorders in biotinidase deficiency are analyzed on the example of a clinical case and a review of the literature. Early diagnosis and administration of biotin therapy play an important role in preventing disease progression and clinical signs.
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