The first reported HLCS gene mutation causing holocarboxylase synthetase deficiency in a Vietnamese patient

Holocarboxylase synthetase deficiency is an inborn error of biotin metabolism leading to multiple carboxylase deficiency which is often biotin responsive. This disease is believed to be relatively common among the Asian population.

A 6-year-old Vietnamese boy presented with recurrent episodes of severe metabolic acidosis precipitated by intercurrent illnesses. An extensive skin rash was present since the onset of his illness. Multiple carboxylase deficiency was considered a likely diagnosis based on the history and the characteristic skin rash.

This diagnosis was later confirmed by urine organic acid and molecular genetic studies. Urine organic acid showed characteristic excretion of glycine conjugates. Serum biotinidase activity was normal. Sequencing of the holocarboxylase synthetase gene revealed the patient being homozygous for a common mutation R508W. The patient showed a dramatic response to biotin within days of its administration.

This case illustrates a potential highly treatable inborn error of metabolism that can be recognized on clinical grounds and its favorable response to biotin treatment.