Mutation Analysis of IL2RG in Human X-Linked Severe Combined Immunodeficiency

Abstract

AbstractSevere combined immunodeficiency (SCID) is a syndrome of profoundly impaired cellular and humoral immunity. In humans, SCID is most commonly caused by mutations in the X-linked gene IL2RG, which encodes the common γ chain, γc, of the leukocyte receptors for interleukin-2 and multiple other cytokines. To investigate the frequency and variety of IL2RG mutations that cause SCID, we analyzed DNA, RNA, and B-cell lines from a total of 103 unrelated SCID-affected males and their relatives using a combination of molecular and immunologic techniques. Sixty-two different mutations spanning all eight IL2RG exons were found in 87 cases, making possible correlations between mutation type and functional consequences. Although skewed maternal X chromosome inactivation, single-strand conformation polymorphism, mRNA expression, and cell surface staining with anti-γc antibodies were all helpful in establishing IL2RG defects as the cause of SCID, only dideoxy fingerprinting and DNA sequence determination each detected 100% of the IL2RG mutations in our series. Abnormal γc chains may be expressed in the lymphocytes of as many as two thirds of patients with X-linked SCID. Specific mutation diagnosis thus remains technically challenging, but it is important for genetic counseling and perhaps for helping to select appropriate subjects for retroviral gene therapy trials.