Reversible metabolic myopathy in biotinidase deficiency: its possible role in causing hypotonia.

A 5-year-old girl diagnosed with biotinidase deficiency at 9 months of age demonstrated limb and axial hypotonia which improved on biotin therapy. In this patient, electromyographic (EMG) studies prior to treatment were compatible with a mild myopathic process. Serial EMGs performed on biotin therapy demonstrated a gradual resolution of the myopathy. This is the first documented case of a reversible myopathy in a patient with biotinidase deficiency, which may contribute to the clinical findings of hypotonia.