Rare Diseases and Medical Genetics, Bambino Gesù Children Hospital, Rome, Italy. Department of Medical and Surgical Sciences of the Mothers, Children and Adults, Paediatric Unit, University of Modena & Reggio Emilia, Modena, Italy. Department of Internal Medicine, University of Genova, Genova, Italy. Department of Life Sciences, University of Modena & Reggio Emilia, Modena, Italy. University Pediatric Hospital Giovanni XXIII, O.U. Metabolic and Genetic Diseases, Bari, Italy. Department of Experimental Medicine and Surgery, University of Rome "Tor Vergata", Rome, Italy. Department of Internal Medicine, University of Genova, Genova, Italy. Electronic address: stefbert@unige.it. Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy. Electronic address: sebcal@unimore.it.