Diagnosis of autoimmune lymphoproliferative syndrome caused by FAS deficiency in adults

Abstract

A diagnosis of autoimmune lymphoproliferative syndrome caused by FAS deficiency during adulthood is unusual. We analyzed 17 cases of autoimmune lymphoproliferative syndrome caused by FAS deficiency diagnosed during adulthood in French reference centers for hereditary immunodeficiencies and for immune cytopenias. Twelve of the 17 patients had developed their first symptoms during childhood. The diagnosis of autoimmune lymphopro-liferative syndrome had been delayed for a variety of reasons, including unusual clinical manifestations, late referral to a reference center, and the occurrence of somatic FAS mutations. The 5 other patients presented their first symptoms after the age of 16 years. In these patients, three germline heterozygous FAS mutations were predicted to be associated with haploinsufficiency and a somatic event on the second FAS allele was observed in 2 cases. Autoimmune lymphoproliferative syndrome may well be diagnosed in adulthood. The occurrence of additional genetic events may account for the delayed disease onset.

Introduction

Autoimmune lymphoproliferative syndrome caused by FAS/TNFRSF6 deficiency (ALPS-FAS) is characterized by: i) early-onset, benign splenomegaly and lymphadenopathy; ii) the accumulation of a mature, polyclonal population of TCRαβ CD4CD8 T cells (referred to as double-negative (DN) T cells); iii) multilineage cytopenia caused by peripheral autoimmune destruction or splenic sequestration; and iv) an increased risk of B-cell lymphoma.41

Most cases of ALPS-FAS result from heterozygous dominant germline FAS mutations. However, homozygous germline mutations have occasionally been reported.2 Somatic heterozygous FAS mutations are also common and account for 10-15% of ALPS-FAS cases. Lastly, when germline FAS heterozygous mutations lead to haploinsufficiency,5 combinations of germline and somatic modifications of the FAS gene have been observed.6 A FAS-mediated apoptosis defect may be assessed in vitro in patients carrying germline mutations but not in those affected by somatic mutations. Plasma biomarkers are now routinely assayed in the pre-diagnosis of ALPS-FAS and include soluble FAS ligand (sFASL), interleukin-10 (IL-10), IL-18 and vitamin B12.87

The onset of ALPS-FAS is typically observed in the first few years of life (on average at 2.5 years of age).31 Late ALPS-FAS onset (i.e. during adulthood) has only been described in a few cases.109

Here, we present data on the clinical, biological and molecular aspects of 17 ALPS-FAS patients diagnosed during adulthood. The data were collated by the French national reference centers for hereditary immunodeficiencies and immune cytopenias.

Design and Methods

We checked patient records at the French National Reference Center for Hereditary Immunodeficiencies (CEREDIH) and the French National Reference Center for Immune Cytopenias for cases of ALPS diagnosed after the age of 16 years. Only confirmed ALPS-FAS patients were selected, i.e. patients with a molecular diagnosis of germinal and/or somatic FAS mutations.1 All participants or their parents/guardians gave their signed, informed consent to the study in accordance with the Declaration of Helsinki. The study was approved by the Ethics Committee Comité de Protection des Personnes Ile de France (Number DC2011-1338). The relative DN T-cell counts were obtained from the local immunology laboratories and confirmed in the Centre d’Etude des Déficits Immunitaires (CEDI) reference laboratory. The CEDI laboratory also identified FAS mutations, analyzed in vitro T-cell FAS-mediated apoptosis, and assayed plasma levels of sFASL and IL-10, as previously described.76

Results

We identified 17 cases of ALPS-FAS in which a molecular diagnosis (i.e. identification of a FAS mutation) had been made after the age of 16 years (Table 1). We then divided this small cohort of adult ALPS-FAS patients into two groups according to the time at which the first manifestations of the condition occurred.

Table 1.Patients’ characteristics and clinical features.

In a first group of 12 patients (group 1), clinical symptoms of ALPS had been present during childhood but the molecular diagnosis had only been made in adulthood (at a mean age of 33 years). In childhood, all but one of the patients had presented with splenomegaly, enlarged lymph nodes and cytopenia. However, the diagnosis had been delayed by a variety of factors. In 6 cases, the molecular diagnosis was made following the identification of FAS mutations in an ALPS-FAS proband with pediatric onset (P1.1; 1.4; 1.6-1.9). In 3 cases (P1.2; 1.3 and 1.5), diagnosis of ALPS-FAS was delayed by interference from a previous diagnosis of Evans syndrome (P1.2 and 1.3) or by an unusual clinical presentation such as hyperviscous syndrome and nephrotic syndrome (P1.5). The diagnosis of ALPS-FAS was made after consultation in a tertiary hospital and analysis of ALPS-FAS-related biomarkers (such as the DN T-cell count and plasma sFASL and IL-10 levels).

For 3 patients (P1.10–1.12) a molecular diagnosis was made following DN T-cell sorting and the identification of somatic FAS mutations.

Interestingly, lymph node and liver biopsies in 3 of these 12 patients had revealed follicular hyperplasia and had prompted a diagnosis of ‘atypical’ Castleman’s disease. When a splenectomy was performed, the histology results were not conclusive and showed only lymphoid hyperplasia.

A variety of FAS mutations were identified (Table 2). In one patient (P1.3), the mutation affected the extracellular domain of FAS and was probably associated with haploinsufficiency. In 11 patients, the FAS mutations affected the intracellular domain. One mutation was predicted to lead to a truncated death domain, whereas 10 were missense mutations.

Table 2.Biomarkers at diagnosis and FAS mutations.

The second group (group 2) was made up of 5 patients who had only displayed their first clinical symptoms of ALPS after the age of 16 years. Four of the 5 patients presented with autoimmune cytopenias (mainly hemolytic anemia). Lymphoproliferation was reported in all 5 patients but was milder than in typical pediatric ALPS-FAS patients. Gamma globulin level was normal in 2 patients, contrasting with frequent hypergammaglobulinemia in infants. In 3 cases (P2.2; 2.4; 2.5), a diagnosis of ALPS was only confirmed after diagnosis of the same condition in a related child. In 2 cases (P2.1 and P2.3), a diagnosis of ALPS-FAS was made after screening for autoimmune manifestations (Evans syndrome with lymphoproliferation and cold agglutinin disease).

In all tested patients, levels of ALPS-specific markers (DN T cells, sFASL and IL-10) were moderately (P2.3 and 2.4) or greatly (P2.2 and P2.5) elevated. The administration of immunosuppressant agents attenuates the elevation of these markers.

Interestingly, three mutations (P2.3; 2.4 and 2.5) were predicted to be associated with haploinsufficiency. This type of mutation is often associated with a secondary somatic event affecting the second FAS allele.6 In 2 patients (P2.2 and 2.5), molecular screening of DNA extracted from sorted DN T cells revealed the loss of the wild-type allele and duplication of the mutated allele.

Discussion

We analyzed 17 cases of ALPS-FAS diagnosed during adulthood in French reference centers for hereditary immunodeficiencies and for immune cytopenias.

Twelve of the 17 patients had developed their first symptoms during childhood. Consideration of this group of patients shows that early-onset ALPS-FAS patients can be misdiagnosed in childhood. The 5 other patients had their first symptoms after the age of 16 years, although we can not exclude the possibility that minor symptoms in childhood went unreported. Unusual clinical manifestations, and the occurrence of somatic FAS mutations which were first described only a few years ago, have led to delayed diagnosis in both groups. In 9 patients, the molecular diagnosis was made following the identification of FAS mutations in a related child with ALPS-FAS. Six of these 9 patients had been symptomatic in childhood more than twenty to thirty years previously, a time at which knowledge of ALPS was not widespread. Although this diagnosis is now an expected consequence of thorough family screening, these cases showed that ALPS symptoms can be less prominent in adulthood than in childhood (Table 1). In such cases, an indolent autoimmune lymphoproliferative syndrome remains in adulthood and constitutes a tricky diagnosis for non-pediatricians who are unfamiliar with ALPS-FAS. Indeed, there are several differential diagnoses for ALPS in adults such as multicentric Castelman’s disease, angioimmunoblastic T-cell lymphoma, and Rosai-Dorfman disease. Chronic lymphopro-liferative syndrome is usually present in these diseases and auto-immune cytopenia is not rare. Physicians should consider ALPS in these situations and also in Evans’s syndrome, which has now been recognized as a heterogeneous syndrome that includes patients with ALPS-FAS.10

The occurrence of lymphoma in 3 of the adult patients reported highlights the need to consider a diagnosis of ALPS-FAS in lymphoma patients with immune cytopenias or chronic benign lymphoproliferation during infancy. The relapse of immune cytopenias in adulthood should also prompt the physician to consider a diagnosis of ALPS.

Assay for plasma biomarkers (such as sFASL, IL-10 and vitamin B12) should facilitate the correct diagnosis of ALPS-FAS in adult patients or in those with unusual presentations.

Interestingly, in the 5 patients with ALPS-FAS late onset, three germline heterozygous FAS mutations were predicted to be associated with haploinsufficiency and a somatic event on the second FAS allele was observed in 2 cases. The occurrence of this type of somatic event could account for the delayed onset of ALPS symptoms in these 2 individuals. Indeed a delayed onset of ALPS symptoms was observed in pediatric patients with combined germline and somatic FAS mutations.3 This may be related to a later occurrence of the somatic events during embryonic development or even after birth. Hence, a limited number of progenitor lymphocytes might carry the causal genetic element thereby delaying the accumulation of pathogenic lymphocytes and onset of first symptoms. The lack of somatic events within the second FAS allele in the other 3 patients might be explained by intronic FAS mutations or mutations in other genes involved in the FAS/FASL signaling pathways, such as the caspase-10 gene.11

Taken as a whole, our data show that ALPS-FAS symptoms can occur in adulthood and not just in misdiagnosed pediatric ALPS-FAS patients. Some patients really do appear to present their first symptoms in adulthood. Biomarker assays are critical in guiding the physician towards a diagnosis of ALPS-FAS. In patients with elevated biomarker levels, molecular screening for somatic events contributed to the diagnosis of ALPS-FAS in 25% of the cases in group 1 and revealed a second genetic event in 2 of the 5 patients in group 2. This indicated that somatic events might account for delayed onset of clinical symptoms in ALPS patients and could pave the way for the characterization of somatic mutations in known genes involved in the FAS/FASL pathway or in newly identified genes involved in key checkpoints of self-tolerance.

Acknowledgments

The authors would like to thank Christophe Chantrain, Daan Dierickxwerner, Guy Leverger, and Nizar Mahlaoui.

Footnotes

• Funding This work was funded by grants from the Fondation pour la Recherche Médicale (to BN), the Agence Nationale pour la Recherche (to FRL) and an advanced grant from the European Research Council (to AF).
• Authorship and Disclosures Information on authorship, contributions, and financial & other disclosures was provided by the authors and is available with the online version of this article at www.haematologica.org.

• Received April 26, 2012.
• Accepted August 27, 2012.