A functional analysis of the putative polymorphisms A91V and N252S and 22 missense perform mutations associated with familial hemophagocytic lymphohistiocytosis

Abstract

Up to 60% of cases of the autosomal recessive immunodeficiency hemophagocytic lymphohistiocytosis (HLH) are associated with mutations in the perform (PRF1) gene. In this study, we expressed wild-type and mutated perform in rat basophil leukemia cells to study the effect on lytic function of the substitutions A91V and N252S (commonly considered to be neutral polymorphisms) and 22 perform missense substitutions first identified in HLH patients. Surprisingly, we found that A91V perform was expressed at reduced levels compared with wild-type perform, resulting in partial loss of lytic capacity. In contrast, expression and function of N252S-substituted perform were normal. Most HLH-associated mutations resulted in protein degradation (probably due to misfolding) and complete loss of perform activity, the exception being R232H, which retained approximately 30% wild-type activity. Several other mutated proteins (H222Q, C73R, F157V, and D313V) had no detectable lytic activity but were expressed at normal levels, suggesting that their functional defect might map downstream at the level of the target cell membrane. One further perform substitution identified in an HLH patient (V183G) was normally expressed and displayed normal lysis. This report represents the first systematic functional analysis of HLH-associated missense mutations and the 2 most common perform polymorphisms. © 2005 by The American Society of Hematology.