Of the patients now reported with NDUFA13 deficiency, 84% had oculomotor abnormalities and 54% had optic atrophy, possibly representing a more specific finding, although eye involvement is frequently observed in other causes of complex I deficiency.7 The reasons for prominent ophthalmological involvement in complex I deficiency remain unknown, as do the precise pathomechanisms underlying the focal necrotic lesions defining Leigh syndrome. The gene discussed is NDUFA13; the disease is hyperinsulinemic hypoglycemia, familial, 4.