[MIM*202500,MIM*300400, and MIM*312863] an immunodeficiency in which there is absence of both humoral and cellular immunity with lymphopenia (of both B-type and T-type lymphocytes); characterized by thymus atrophy, lack of delayed hypersensitivity, and marked susceptibility to infections by bacteria, viruses, fungi, protozoa, and live vaccines; although bone marrow transplants have been effective, death may occur in the first year of life. Both autosomal recessive and X-linked forms occur; about half of those affected with autosomal recessive SCID have adenosine deaminase deficiency. The X-linked form is caused by mutation in the interleukin-2 receptor gamma gene (IL2RG) on Xq. SYN: Swiss type agammaglobulinemia.