A severe combined immunodeficiency that is the most severe form of SCID and has_material_basis_in mutations in the gene encoding mitochondrial adenylate kinase 2. It is characterized by congenital agranulocytosis, lymphopenia, and lymphoid and thymic hypoplasia with absent cellular and humoral immunity functions. [ http://purl.obolibrary.org/obo/ECO_0007636 ]