Molecular genetic haplotype segregation studies in three families with X-linked lymphoproliferative disease

Treatment of HCV infection with interferon alpha-2b and ribavirin in a patient with X-linked lymphoproliferative syndrome

Chronic hepatitis C (HCV) infection in patients with primary immunodeficiency increases the risk of an accelerated progression of HCV-related liver disease. Here, we report a patient with X-linked lymphoproliferative syndrome infected with HCV and Epstein-Barr virus (EBV). After combination treatment with interferon alpha-2b and ribavirin, clearance of HCV-RNA was achieved, and noteworthily, EBV DNA also became undetectable.

X-linked lymphoproliferative disease: three atypical cases

Common variable immunodeficiency (CVID) is the most frequently occurring primary immunodeficiency in both children and adults. The molecular basis of CVID has not been defined, and diagnosis involves exclusion of other molecularly defined disorders. X-linked lymphoproliferative disease (XLP) is a rare disorder in which severe immunodysregulatory phenomena typically follow Epstein-Barr virus (EBV) infection. Boys who survive initial EBV infection have a high incidence of severe complications, including progressive immunodeficiency, aplastic anaemia, lymphoproliferative disease and lymphoma. Survival beyond the second decade is unusual, although bone marrow transplantation can be curative. Until recently reliable diagnostic testing for XLP has not been available, but the identification of the XLP gene, known as SH2D1A, and coding for a protein known as SAP, means that molecular diagnosis is now possible, both by protein expression assays, and mutation detection, although the mutation detection rate in several series is only 55-60%. We describe three male patients initially diagnosed as affected by CVID, one of whom developed fatal complications suggestive of XLP, and all of whom lack expression of SAP. Two out of three have disease-causing mutations in the SAP gene, consistent with published data for XLP. These findings raise the possibility that a subgroup of patients with CVID may be phenotypic variants of XLP. Further studies are necessary to investigate this possibility, and also to clarify the prognostic significance of SAP abnormalities in such patients in the absence of typical features of XLP.

Large deletion of the X-linked lymphoproliferative disease gene detected by fluorescence in situ hybridization

The X-linked lymphoproliferative disease (XLP) is an inherited immunodeficiency characterized by an abnormal responses to infection with Epstein-Barr virus (EBV), resulting in fatal infectious mononucleosis, hypogammaglobulinemia, virus-associated hemophagocytic syndrome, and malignant lymphoma. Mutations in the gene coding for a T cell-specific SLAM-associated protein (SAP) have been recently identified in XLP patients. We report on a 1-year-old boy representing fulminant hemophagocytic syndrome. He developed high fever, lymphadenopathy, hepatosplenomegaly with liver dysfunction, and pancytopenia with marrow hemophagocytosis. EBV DNA was abnormally increased in the blood. Polymerase chain reaction failed to amplify SAP mRNA and genomic DNA products from the patient' As peripheral blood. A large deletion of the SAP gene was confirmed by fluorescence in situ hybridization (FISH). FISH analysis also disclosed that the patient's mother was a carrier. We conclude that FISH can be useful in the diagnosis of XLP with large deletions of the SAP gene and its carrier state.

Epstein-Barr virus-negative boys with non-Hodgkin lymphoma are mutated in the SH2D1A gene, as are patients with X-linked lymphoproliferative disease (XLP)

X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency, which most often manifests itself after Epstein-Barr virus (EBV) infection. The main clinical phenotypes include fulminant or fatal infectious mononucleosis, dysgammaglobulinaemia and malignant lymphoma. We have recently cloned the SH2D1A gene, which has been shown to be mutated in approximately 70% of XLP patients. Now we report five novel SH2D1A mutations in patients from five unrelated XLP families. No mutations were found in another three XLP families. In three boys with early onset non-Hodgkin lymphoma (NHL) from two unrelated families a deletion of SH2D1A exon 1 and a splice site mutation were found, respectively. These patients did not show any laboratory or clinical signs of a previous EBV infection. A fourth EBV-uninfected and unrelated boy with a stop mutation in the SH2D1A gene shows only signs of dysgammaglobulinaemia. Development of dysgamma-globulinaemia and lymphoma without evidence of prior EBV infection in four of our patients suggests that EBV is unrelated to these phenotypes, in contrast to fulminant or fatal infectious mononucleosis. The role of SH2D1A as a putative tumour suppressor gene remains to be investigated.

Host response to EBV infection in X-linked lymphoproliferative disease results from mutations in an SH2-domain encoding gene

X-linked lymphoproliferative syndrome (XLP or Duncan disease) is characterized by extreme sensitivity to Epstein-Barr virus (EBV), resulting in a complex phenotype manifested by severe or fatal infectious mononucleosis, acquired hypogammaglobulinemia and malignant lymphoma. We have identified a gene, SH2D1A, that is mutated in XLP patients and encodes a novel protein composed of a single SH2 domain. SH2D1A is expressed in many tissues involved in the immune system. The identification of SH2D1A will allow the determination of its mechanism of action as a possible regulator of the EBV-induced immune response.

Primary immunodeficiencies

The primary immunodeficiencies are congenital disorders that affect the function of the immune system. The result is an inadequate immune response to microorganisms, self-antigens, and tumor cells, which leads to increased susceptibility to infections, autoimmunity, or malignant disease. A substantial advance has been made in the understanding of the exact molecular mechanisms leading to primary immunodeficiencies; however, for some types, a specific genetic defect has not yet been determined. The life expectancy of patients with primary immunodeficiencies has increased considerably because of bone marrow transplantation and replacement therapies. Gene therapy has already been used for a particular type of immunodeficiency and is a promising alternative for the future management of many other types of primary immunodeficiencies. A better understanding of the genetic defects that lead to primary immunodeficiencies would result in the development of novel therapeutic strategies.

Prenatal diagnosis of X linked lymphoproliferative disease using multiplex polymerase chain reaction

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