We report a 36-year-old woman who exhibited progressive optic atrophy at 13 years old, then stroke-like episodes and spastic diplegia in her 20s. Biotinidase deficiency was not readily considered in the differential diagnosis, and the definitive diagnosis was not made until pathological variants of the biotinidase gene (BTD) were found by exome sequencing. Profound biotinidase deficiency was confirmed by enzyme analysis. Unfortunately, her symptoms did not resolve or improve with biotin treatment. Biotin therapy is essential for all individuals with profound biotinidase deficiency and for preventing further damage in those who already exhibit irreversible neurological damage. Newborn screening for the disorder would have avoided years of clinical symptoms that now appear to be irreversible with biotin treatment.