Mutation analysis by a non-radioactive single-strand conformation polymorphism assay in nine families with X-linked severe combined immunodeficiency (SCIDX1)

Maternal T-cell engraftment associated with severe hemophagocytosis of the bone marrow in untreated X-linked severe combined immunodeficiency

Maternal engraftment of T cells in severe combined immunodeficiency can lead to graft-versus-host disease of the skin and liver. We report the case of an infant with X-linked severe combined immunodeficiency, confirmed by DNA sequencing of the common gamma chain gene locus, in which this disorder's characteristic peripheral lymphocyte phenotype [T(-)B(+)NK(-)] was obscured by the postnatal onset of hemophagocytic syndrome that included severe B-cell lymphopenia, neutropenia, and anemia. Hemophagocytosis was most likely owing to maternal graft-versus-host disease, as perforin-expressing CD8 T cells, presumably of maternal origin, were prominent in the bone marrow and there was no concurrent severe infection.

Development of autologous T lymphocytes in two males with X-linked severe combined immune deficiency: molecular and cellular characterization

We report on two patients affected with severe combined immune deficiency (SCID) with an unusual immunological phenotype and a substantial number of autologous, poorly functioning T cells. Distinct mutations identified at the IL2RG locus in the two patients impaired IL-2-mediated signaling but affected T-cell lymphopoiesis differently, resulting in generation of a polyclonal or oligoclonal T-cell repertoire. These observations add to the growing complexity of the immunological spectrum of SCID in humans and indicate the need for detailed immunological and molecular investigations in atypical cases.

Efficient detection of thirty-seven new IL2RG mutations in human X-linked severe combined immunodeficiency

X-linked severe combined immunodeficiency (XSCID) is a rare and potentially fatal disease caused by mutations of IL2RG, the gene encoding the interleukin-2 receptor gamma chain, a component of multiple cytokine receptors that are essential for lymphocyte development and function. To date, over 100 different mutations of IL2RG resulting in XSCID have been published. Using nonradioactive, direct DNA sequencing of a single PCR amplicon containing the whole IL2RG gene, we found IL2RG mutations in 78 previously unpublished unrelated cases of XSCID. We report 37 newly identified mutations of IL2RG, including 23 point mutations, 10 small deletions, 3 instances of the same single nucleotide insertion, 1 large deletion, and 2 complex mutations. More than half of the mutations (22 of 37) were predicted to result in unstable IL2RG mRNA. The remaining 14 mutations disrupted conserved functional motifs common to all cytokine receptor family members; changed protein conformation, charge, or hydrophobicity; or altered the intracellular portion of the protein, which is critical for proper interaction with signal-transducing molecules including Janus family tyrosine kinase 3.

Haemophagocytic lymphohistiocytosis in X-linked severe combined immunodeficiency

Haemophagocytic lymphohistiocytosis (HLH) is characterized by destruction of haematopoietic elements, and is associated with a variety of manifestations including immune abnormalities. We describe an infant with HLH who had no evidence of infection or malignancy. He had markedly reduced natural killer (NK) and T-cell numbers and mitogen responses, consistent with severe combined immune deficiency. Western blot and flow cytometry analyses revealed an absence of interleukin (IL)-2 receptor gamma (gamma common) chain expression and a transition (C --> T) at nucleotide 684 in the gamma common gene. This novel case highlights the need for a thorough evaluation of immunological phenotype and genotype in patients with HLH.

Identification of X-linked severe combined immunodeficiency by mutation analysis of blood and hair roots

Severe combined immunodeficiency is a heterogenous syndrome of varied genetic origins of which the X-linked type is the commonest (XSCID). The most sensitive method for diagnosis of XSCID in the absence of X-linked inheritance pattern is by mutation analysis. In this report we have performed mutation analysis in 13 unrelated boys transplanted (BMT) for SCID without a known cause to determine the frequency of XSCID. Five boys had an affected male relative. We also assessed the utility of hair roots for children without pre-transplant blood stored for mutation analysis since donor genotype was expressed in peripheral blood post BMT. Screening was performed by analysis of single-strand conformational polymorphism (SSCP) followed by sequencing of candidate exons. Mutations were found in 11 cases, of which six were sporadic, and maternal mosaicism was found in one family. Three mothers of the six sporadic cases were identified as carriers. The majority (6/8) of boys with SCID had gammac deficiency despite the absence of X-linked inheritance pattern. The significant frequency of de novo mutations and the occurrence of maternal germline mosaicism highlights the importance of mutation analysis. The strategy of using DNA from hair roots was particularly valuable where no pre-transplant blood was stored. Characterization of the mutations will also enable research into the correction of these genetic defects.