More significantly and unexpectedly, mutations in the mitochondrial AK2 (adenylate kinase 2) gene have been identified in individuals affected with reticular dysgenesis, the most severe form of inborn severe combined immunodeficiencies (SCID), which is associated with sensorineural deafness, a process where nucleotide signaling, cell motility and ciliary functions are involved [9,10]. The gene discussed is AK2; the disease is severe combined immunodeficiency.