HmtDB, a Human Mitochondrial Genomic Resource Based on Variability Studies Supporting Population Genetics and Biomedical Research by Pappadà Graziano, Scioscia Gaetano, Lascaro Daniela, Santamaria Monica, Accetturo Matteo, Attimonelli Marcella, Russo Luigi, Zanchetta Luigi, Tommaseo-Ponzetta Mila