A 12-month-old boy was referred to the metabolic centre because of a 4-week history of vomiting, diarrhoea, progressive muscular hypotonia, mycotic skin infection and partial alopecia. He had severe metabolic acidosis compensated by hyperventilation (pCO2 17 mmHg). Laboratory investigations revealed hyperlactacidaemia (9.7 mmol/l) and hyperalaninaemia (830 mmol/l). Increased excretion of 3-OH-isovaleric acid (925 mg/g creatinine) and lactic acid (11 496 mmol/mol creatinine) were found in urine. Biotinidase deficiency was suspected because of concomitant neurologic abnormalities, dermatological symptoms and metabolic disturbances. The diagnosis of biotinidase deficiency was confirmed by enzymatic assay in plasma (biotinidase activity 0.4 nmol PABA/min/ml, controls 5.5 - 10.2 nmol PABA/min/ml). Activity of biotidinase in parents, brother and in three other relatives were between 17 - 70% of controls. Within several days after beginning of treatment with biotin (20 mg/day) total clinical recovery and normalisation of hyperlactacidaemia were observed. Up to now the boy’s psychomotor development is normal, only MR study of the brain carried out 9 months after the beginning of treatment showed the same cortical atrophy as before therapy. Although the incidence of biotinidase deficiency is estimated at 1 per 40 000 births, to our knowledge this is the first case in the Czech Republic and only the second one in the region of the former Czechoslovak Republic. We suppose that some children with biotinidase deficiency are lost unrecognised. Children with treated biotinidase deficiency have a good prognosis, but a prolonged follow-up is necessary.

        Key words: biotionidase deficiency, lactic acidosis