MedGen

Severe combined immunodeficiency refers to a genetically and clinically heterogeneous group of disorders with defective cellular and humoral immune function. Patients with SCID present in infancy with recurrent, persistent infections by opportunistic organisms, including Candida albicans, Pneumocystis carinii, and cytomegalovirus, among many others. Laboratory analysis shows profound lymphopenia with diminished or absent immunoglobulins. The common characteristic of all types of SCID is absence of T cell-mediated cellular immunity due to a defect in T-cell development. Without treatment, patients usually die within the first year of life. The overall prevalence of all types of SCID is approximately 1 in 75,000 births (Fischer et al., 1997; Buckley, 2004). Genetic Heterogeneity of SCID SCID can be divided into 2 main classes: those with B lymphocytes (B+ SCID) and those without (B- SCID). Presence or absence of NK cells is variable within these groups. The most common form of SCID is X-linked T-, B+, NK- SCID (SCIDX1; 300400) caused by mutation in the IL2RG gene (308380) on chromosome Xq13.1. Autosomal recessive SCID includes T-, B-, NK+ SCID, caused by mutation in the RAG1 and RAG2 genes on 11p13; T-, B+, NK- SCID (600802), caused by mutation in the JAK3 gene (600173) on 19p13; T-, B+, NK+ SCID (IMD104; 608971), caused by mutation in the IL7R gene (146661) on 5p13; T-, B+, NK+ SCID (IMD105; 619924), caused by mutation in the CD45 gene (PTPRC; 151460) on 1q31-q32; T-, B+, NK+ SCID (IMD19; 615617), caused by mutation in the CD3D gene (186790) on 11q23; T-, B-, NK- SCID (102700) caused by mutation in the ADA (608958) gene on 20q13; and T-, B-, NK+ SCID with sensitivity to ionizing radiation (602450), caused by mutation in the Artemis gene (DCLRE1C; 605988) on 10p13 (Kalman et al., 2004); T-, B+, NK+ SCID with intellectual disability, spasticity, and craniofacial abnormalities (IMD49; 617237), caused by mutation in the BCL11B gene (606558) on 14q32; and T-, B-, NK+ SCID with microcephaly, growth retardation, and sensitivity to ionizing radiation (IMD124; 611291), caused by mutation in the NHEJ1 gene (611290) on 2q35. Approximately 20 to 30% of all SCID patients are T-, B-, NK+, and approximately half of these patients have mutations in the RAG1 or RAG2 genes (Schwarz et al., 1996; Fischer et al., 1997). [from OMIM]

Severe combined immunodeficiency-104 (IMD104) is an autosomal recessive disorder characterized by the onset of recurrent infections in early infancy. Manifestations may include oral thrush, fever, and failure to thrive. Some patients have lymphadenopathy and hepatosplenomegaly, whereas others have absence of lymph nodes and lack a thymic shadow. Laboratory studies show decreased or absent numbers of nonfunctional T cells, normal or increased levels of B cells, variable hypogammaglobulinemia, and normal NK cells. The disorder is caused by a defect in IL7 (146660) signaling due to a mutant IL7 receptor. Hematopoietic stem cell transplantation may be curative (Roifman et al., 2000 and Giliani et al., 2005). Giliani et al. (2005) provided a detailed review of IL7R deficiency, including discussion of the IL7R gene and its function in the immune system, clinical features of the disorder, and experiences with hematopoietic stem cell transplant as treatment. For a general phenotypic description and a discussion of genetic heterogeneity of autosomal recessive SCID, see 601457. [from OMIM]

Insufficient weight gain or inappropriate weight loss for a child, that is attributed to an endogenous recurrent infections. [from HPO]