Nephrocalcinosis and retinal dystrophy, rare manifestations of MPV17-related mitochondrial depletion syndrome?☆

With interest we read the article by Kim et al. about four pediatric patients with hepato-cerebral mitochondrial depletion-syndrome(MDS) due toMPV17-mutations who all died from hepatic failure a fewmonths after birth [1]. We have the following comments and concerns. Nephrocalcinosis is an uncommon phenotypic manifestation of MPV17-mutations. Only in a single patient with MDS due to a RRMB2 mutation has nephrocalcinosis been reported [2]. Are there indications that nephrocalcinosis was due to causes other than the MPV17mutation? Was the family history positive for nephrocalcinosis? Was there hyperparathyroidism, heart failure, prolonged hypercalcemia, placenta previa, placenta abruptio, or schock in patient-1? Another not yet reported manifestation of a MPV17-mutation is retinal dystrophy [1]. Which type of retinal dystrophy was diagnosed? Retinitis pigmeentosa, Best's disease, or Stargadt's disease?Were causes other than the MPV17-mutation excluded as cause of reatinal dystrophy? Cardiac manifestations are also a rare clinical manifestation of the MPV17-mutation. Was any of the four investigated for cardiac disease? Was there cardiomyopathy, arrhythmias, or conduction defects? Was the individual or family history positive for palpitations, syncope, heart failure, or sudden cardiac death? Contrary to nephrocalcinosis, retinal dystrophy, and cardiac disease, polyneuropathy is a common phenotypic feature of MPV17-mutations