Combined Immunodeficiency, X-Linked

A number sign (#) is used with this entry because X-linked combined immunodeficiency (CIDX) is caused by mutation in the gene encoding the gamma subunit of the interleukin-2 receptor (IL2RG; 308380).

X-linked severe combined immunodeficiency (SCIDX1; 300400) is caused by mutation in the same gene.

Clinical Features

Brooks et al. (1990) described a family in which 5 living males had a form of combined immunodeficiency inherited in an X-linked recessive pattern. The disorder was different from the previously described forms of X-linked immunodeficiency and specifically different from SCIDX1. The age of the 5 affected males ranged from 2.5 to 34 years. The most prominent clinical abnormalities were paucity of lymphoid tissue; recurrent sinusitis, otitis media, bronchitis, and pneumonia; severe varicella; and chronic papillomavirus infections. Immunologic analysis showed normal concentrations of serum immunoglobulins, but restricted formation of IgG antibodies to immunogens; normal numbers of B cells and NK cells but decreased numbers of CD4+ and CD8+ T lymphocytes; diminished proliferative responses of blood T cells to allogeneic cells, mitogens, and antigens; and decreased production of interleukin-2 (IL2; 146680) by mitogen-stimulated blood lymphocytes. The pedigree showed that 2 affected males, both deceased, had produced children; all 3 of the children, 1 male and 2 females, were unaffected, but 1 female had an affected son, thus proving herself to be a carrier.

Schmalstieg et al. (1995) showed that X-chromosome inactivation in obligate carriers of CIDX is nonrandom in T and B lymphocytes, as in SCIDX1. X-chromosome inactivation in polymorphic nuclear leukocytes was variable.

Sharfe et al. (1997) reported a child who was normal until the age of 9 months when he developed progressive respiratory symptoms caused by Pneumocystis carinii, which was treated successfully with trimethoprim-sulfamethazole. Physical examination was normal, with normal numbers of peripheral T and B cells, normal cervical lymph nodes, and a normal thymus gland viewed by ultrasonography and biopsy. Although immunoglobulin subtypes were normal, the patient had defective humoral immunity. T cells showed an unusual lack of response to exogenous IL2 The patient received a matched unrelated bone marrow transplantation and was doing well at the time of report. A maternal male cousin had previously been diagnosed with an unusual combined immunodeficiency with normal numbers of both B and T peripheral lymphocytes and normal levels of immunoglobulins and specific antibodies. That patient died at the age of 2 years after a mismatched bone marrow transplant following lectin T-cell depletion.

Molecular Genetics

In 3 related males with CIDX, Schmalstieg et al. (1995) identified a mutation in the IL2RG gene (308380.0008). A normal brother did not have the mutation.

In a child with CIDX, Sharfe et al. (1997) identified a mutation in the IL2RG gene (308380.0012). The authors noted that mutations in the IL2RG gene can result in a spectrum of immunologic phenotypes.