FAS-Mediated Apoptosis Assay in Patients with ALPS-like Phenotype Carrying CASP10 Mutations

INTRODUCTION: Autoimmune lymphoproliferative syndrome (ALPS) is a rare congenital disorder characterized by an impaired FAS-mediated apoptosis that leads to chronic benign lymphoproliferation and autoimmunity. In most cases mutation on FAS gene are responsible of the disease and the phenotype of individuals carrying the same variants can vary from asymptomatic/mild forms to severe disease, due to incomplete penetrance of pathogenic mutations. More rarely, other genes involved in this pathway, such as CASP10, are mutated. Few clinical and molecular data have been reported on small numbers of patients carrying CASP10 mutation showing that different genetic variations can produce contrasting phenotypic effects. So far, 2 mutations have been recognized as pathogenic (I406L and L258F) and other have been reported with controversial result on their pathogenicity (V410l, Y446C) or are known to be polymorphic variants (L522l)

AIMS: The aim of this study is to evaluate the FAS-mediated apoptosis function in patients with ALPS or ALPS-like symptoms carrying mutations on CASP10 gene.

METHODS: We evaluated FAS-mediated apoptosis pathway in all patients presenting with an ALPS/ALPS-like phenotype that were found to carry a CASP10 mutation in our Institution. Molecular findings were obtained by NGS analysis of a panel of genes involved in the most common immune-dysregulation syndromes and immune-deficiencies and were confirmed by Sanger sequencing. Functional studies were performed by Western blot analysis of CASP10, CASP8, and PARP proteins after TRIAL-induced apoptosis stimulation. Healthy individuals were used as control.

RESULTS: We identified 6 patients with ALPS (2) or ALPS-like (4) phenotype, carrying the following heterozygous CASP10 mutations: I406L (1), V410l (2), Y446C (1) L522l (2). Western blot analysis showed an impaired activation of CASP10, CASP8, and PARP proteins in all cases compared to healthy control (Fig. 1)

CONCLUSIONS: In our symptomatic patients, the CASP10 polymorphic variant L522l and other mutations whose pathogenicity is controversial (V410l, Y446C) were associated with impaired CASP10, CASP8, PARP activity -and therefore with apoptosis dysfunction- as in the case of I406L pathogenic mutation. We can speculate that, in addition to the functional impairment of apoptosis, other genetic and epigenetic factors might be crucial for the development of clinical symptoms in CASP10 mutated patients, as already described in FAS mutations, suggesting that the search of other mutations in patients with ALPS/ALPS-like phenotype should be encouraged. Nonetheless, further studies on epigenetic factors potentially implicated in the expression of symptoms are needed to fully understand the heterogeneity of clinical phenotype of this disorder.

Figure 1.

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Figure 1.

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