Mitochondrial disorders are varied in their clinical presentation and pathogenesis. Diagnosis is usually made clinically and genetic defects are often not identified. We present a 6-year-old female patient with a diagnosis of a mitochondrial disorder secondary to complex I deficiency with seizures and developmental delay from infancy. Glucose transporter deficiency was suspected after a lumbar puncture showed hypoglycorrhachia. Her disorder was confirmed genetically as a mutation in her solute carrier family 2, facilitated glucose transporter member 1 (SLCA2) gene. Delayed diagnosis led to delayed treatment, and neurologic sequelae may have been prevented by earlier recognition of this disorder.