A form of SCID characterized by profound lymphopenia and very low immunoglobulin levels of all isotypes resulting in severe and recurrent opportunistic infections. The disease is severe combined immunodeficiency, autosomal recessive, T cell-negative, B cell-negative, NK cell-negative, due to adenosine deaminase deficiency (MONDO_0007064). Also known as: ADA, ADA deficiency, ADA-SCID, SCID due to ADA deficiency, SCID due to ADA deficiency, early-onset, SCID due to adenosine deaminase deficiency, adenosine deaminase deficiency, adenosine deaminase deficiency, partial, Autosomal recessive, Somatic mosaicism.