XIAP deficiency and MEFV variants resulting in an autoinflammatory lymphoproliferative syndrome

A 16-year-old boy of Caucasian ethnicity was evaluated for recurrent febrile episodes occurring during most of his life without establishment of any microbial aetiology. During febrile episodes he developed extensive splenomegaly, lymphadenopathy, anaemia, severe abdominal pain and general malaise. Lymph node biopsies demonstrated inflammation and sinus histiocytosis but no malignancy or granuloma. The patient underwent seroconversion for Epstein-Barr virus (EBV) infection during the hospitalisation. Genetic testing identified a hemizygous frameshift mutation in the X linked inhibitor of apoptosis (XIAP)-gene as well as variants in the MEFV gene indicating Familial Mediterranean Fever (FMF). XIAP expression was markedly reduced in the patient, while a functional assay assessing tumour necrosis factor (TNF)α production of monocytes in response to NOD2 stimulation displayed reduced activity. We suggest that the heterozygous MEFV variants and the hemizygous XIAP variant in combination triggered the prolonged and pathological inflammatory response to EBV infection.