Exonic deletion of CASP10 in a patient presenting with systemic juvenile idiopathic arthritis, but not with autoimmune lymphoproliferative syndrome type IIa.

Systemic juvenile idiopathic arthritis (s-JIA) is a rare inflammatory disease classified as a subtype of chronic childhood arthritis, manifested by spiking fever, erythematous skin rash, pericarditis and hepatosplenomegaly. The genetic background underlying s-JIA remains poorly defined. To detect copy number variations, we performed single nucleotide polymorphism (SNP) array analysis in 50 patients with s-JIA. We found a 13-kb intragenic deletion of CASP10 in one patient. RT-PCR of the mRNA extracted from the patient's lymphoblastoid cells revealed that CASP10 mRNA was truncated. Sequencing the mRNA revealed that this deletion resulted in a frame shift with an early stop codon. CASP10 is known as a causative gene for autoimmune lymphoproliferative syndrome (ALPS) type IIa, another childhood syndrome of lymphadenopathy and splenomegaly associated with autoimmune haemolytic anaemia and thrombocytopenia. TCR αβ(+) CD4/CD8 double-negative T cells in the peripheral blood as a diagnostic marker of ALPS were not high in this patient and lymphocyte apoptosis induced by anti-Fas antibody was normal, denying ALPS in the patient. The father and a sister of the patient showing no symptoms of ALPS or s-JIA, also had the same deletion. Furthermore, we found no other mutations of CASP10 in the other 49 s-JIA patients. These data suggest that the pathogenic significance of CASP10 mutations should be carefully evaluated in s-JIA or even ALPS type IIa in further studies.