A progressive optic nerve atrophy had already been noted at the time of treatment initiation. In these individuals,however, no further optic deterioration was observed when the treatment had been introduced. In all symptomatic patients sensorineural hearing loss did not reverse despite biotin supplementation, however no progression was observed either. Alopecia, which is considered to be a common and characteristic feature of BTD was found 4 patients (18.2%). Asymptomatic patients, who began the treatment with oral biotin did not present with any signs nor symptoms of BTD.