A 5-year-old Indian boy presented with subacute onset regression of milestones associated with seizures and spasticity. The symptoms started after an attack of measles. The magnetic resonance imaging (MRI) of the brain showed cavitating leukodystrophy with posterior predominance. Molecular analysis of the APOPT1 gene, a recently described gene associated with mitochondrial leukodystrophy, showed the patient to be homozygous for a 12.82-kilobase deletion, including coding exon 3. Deletion of exon 3 produces a frameshift, predicting the translation of a truncated protein (p.Glu121Valfs*4). The patient was started on mitochondrial cocktail regimen of thiamine, riboflavin, coenzyme Q and carnitine. Although he initially showed some improvement, he died 6 months after the onset of his illness.