Pathogenic variants in ADA and IL7R account for 5-20% of all cases of SCID, while variants in all other genes, including DCLRE1C, account for ~10% of SCID (Allenspach et al. Variants in IL2RG are causative for X-linked SCID and account for ~40-60% of all cases (Allenspach et al. To date, over 20 genes causative for autosomal recessive forms of SCID, including DCLRE1C, have been identified (Allenspach et al. ![]() Early hematopoietic stem cell transplantation (HSCT) is the most established treatment for patients with SCID (Kwan et al. In general, the prognosis is poor if there is a delay in diagnosis and therapy. The recurrence risk and prognosis may vary depending on the underlying genetic cause of the deficiency. Regardless of the type of SCID, it is necessary to establish a genetic diagnosis for genetic counseling, prognostication, and optimization of treatment (Kwan et al. OS is due to hypomorphic variants predominantly in the RAG1 and RAG2 genes, but DCLRE1C and IL7R can also have causative variants (Villa et al. Patients with OS have limited B cells and elevated T cell levels with impaired function resulting in a distinct inflammatory phenotype (T+B-NK+ SCID). Omenn Syndrome (OS), also known as leaky SCID, typically presents during the first year of life and is characterized by erythroderma, desquamation, eosinophilia, failure to thrive, lymphadenopathy and chronic diarrhea (Ege et al. PubMed ID: 25138334).Ĭlassification of SCID may be subdivided based on B cell status and further subdivided based on NK cell status (Allenspach et al. PubMed ID: 14724556 Sarzotti-Kelsoe et al. Previous studies have shown that DCLRE1C pathogenic variants are a rare cause of SCID as compared to the other genetic causes (Lindegren et al. ![]() Patients with this form of SCID are sensitive to ionizing radiation and chemotherapeutic agents (Kumrah et al. Patients with SCID due to pathogenic variants in DCLRE1C lack T and B cells while retaining normal NK cell levels (T-B-NK+ SCID Bousfiha et al. The majority of the genes are involved in autosomal recessive SCID however IL2RG is associated with an X-linked form of the disease (Allenspach et al. To date, there are over 20 genes known to be associated with SCID (Allenspach et al. ![]() The clinical features associated with SCID include recurrent and severe bacterial, viral, and fungal infections that begin in infancy (Fischer. SCID is caused by genetic defects that inhibit lymphocyte development and function, resulting in no T cell differentiation and abnormal development of B and natural killer (NK) lymphocytes (Fischer. While the true incidence of SCID is unknown, newborn screening studies suggest that 1 in 70,000 births are affected with a range of 1 in 40,000 to 100,000 (Fischer. Severe combined immunodeficiency (SCID) encompasses a diverse group of rare, life-threatening disorders.
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