X-linked severe combined immunodeficiency

X-linked severe combined immunodeficiency (X-SCID) is an immunodeficiency disorder in which the body produces very few T cells and NK cells. In the absence of T cell help, B cells become defective. It is an X-linked recessive inheritance trait, stemming from a mutated (abnormal) version of the IL2RG gene located on the X-chromosome. This gene encodes the interleukin receptor common gamma chain protein, which is a cytokine receptor sub-unit that is part of the receptors for IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21. People with X-SCID often have infections very early in life, before three months of age. This occurs due to the decreased amount of immunoglobulin G (IgG) levels in the infant during the three-month stage. This is followed by viral infections such as pneumonitis, an inflammation of the lung which produces common symptoms such as cough, fever, chills, and shortness of breath. A telltale sign of X-SCID is candidiasis, a type of fungal infection caused by Candida albicans. Candidiasis involves moist areas of the body such as skin, the mouth, respiratory tract, and vagina; symptoms of oral candidiasis include difficulty in swallowing, pain on swallowing and oral lesions. Recurrent eczema-like rashes are also a common symptom. Other common infections experienced by individuals with X-SCID include diarrhea, sepsis, and otitis media. Some other common symptoms that are experienced by X-SCID patients include failure to thrive, gut problems, skin problems, and muscle hypotonia. In some patients symptoms may not appear for the first six months after birth. This is likely due to passive immunity received from the mother in order to protect the baby from infections until the newborn is able to make its own antibodies. As a result, there can be a silent period where the baby displays no symptoms of X-SCID followed by the development of frequent infections. X-SCID is caused by a mutation occurring in the xq13.1 locus of the X-chromosome. Most often, this disease affects males whose mother is a carrier (heterozygous) for the disorder.