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Blood, 15 August 2006, Vol. 108, No. 4, pp. 1306-1312. Prepublished online as a Blood First Edition Paper on April 20, 2006; DOI 10.1182/blood-2006-04-015776.
IMMUNOBIOLOGY A homozygous Fas ligand gene mutation in a patient causes a new type of autoimmune lymphoproliferative syndromeFrom the Servicio de Inmunología and Unidad de Inmunodeficiencias, Hospital Universitario 12 de Octubre, Madrid; Departamento de Bioquímica, Biología Molecular y Celular, Universidad de Zaragoza; and Servicio de Inmunología, Hospital Ramón y Cajal, Madrid, Spain.
Autoimmune lymphoproliferative syndrome (ALPS) is characterized by lymphoproliferation and autoimmune clinical manifestations and is generally caused by defective Fas-mediated apoptosis. This report describes the first homozygous FASL gene mutation in a woman with clinical and immunologic features of ALPS. T-cell blasts from the patient did not induce FasL-mediated apoptosis on Fas-transfected murine L1210 or on Jurkat cells, and activation-induced cell death was impaired. Furthermore, Fas-dependent cytotoxicity was drastically reduced in COS cells transfected with the mutant FasL. In addition, FasL expression on T-cell blasts from the patient was similar to that observed in a healthy control, despite its bearing the high-producer genotype 844C/C in the FASL promoter. Sequencing of the patient's FASL gene revealed a new mutation in exon 4 (A247E). The location of A247E in the FasL extracellular domain and the conservation of the protein sequence of that region recorded in 8 species different from humans support the essential role of FasL COOH terminal domain in Fas/FasL binding. These findings provide evidence that inherited nonlethal FASL abnormalities cause an uncommon apoptosis defect producing lymphoproliferative disease, and they highlight the need for a review of the current ALPS classification to include a new ALPS type Ic subgroup.
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