Another 35 year old male patient has severe systemic disease which includes stable chronic renal failure with secondary hypertension and hyperparathyroidism (eGFR 21 ml/min/1.73m2, PTH 67 pmol/L (RI:1.6–6.9)), bilateral optic atrophy with significant visual impairment in the left eye and bilateral moderate to severe sensorineural hearing loss. The gene discussed is PTH; the disease is Leber hereditary optic neuropathy.