X-LINKED LYMPHOPROLIFERATIVE DISORDER (DUNCAN DISEASE)
This condition affects about 3 per million males, and the gene has been mapped to Xq25. Affected males are susceptible to severe infectious mononucleosis infections (fatal in 50 %, often in childhood), and 25 % develop malignant lymphoma, typically Burkitt-type non-Hodgkin lymphoma in the ileocecal region, but CNS, hepatic, and renal lymphomas are also common. Systemic vasculitis is a rare complication (Dutz et al. 2001). X- linked lymphoproliferative disorder is caused by mutations in the SH2 domain protein 1A (SH2D1A) gene (Sumegi et al. 2000). At least one-quarter of all mutations are missed by direct sequencing, so there may be a role for other, function-based assays in definite cases or in possible heterozygotes (Tabata et al. 2005).