The manifestations are lymphadenopathy, hepatosplenomegaly with or without hypersplenism, and autoimmune disease, mostly directed toward blood cells. In addition, the risk of lymphoma is increased.
ALPS-FAS
ALPS-FAS is the most common and best-characterized type of ALPS. The following are the main consequences of perturbed lymphocyte homeostasis in ALPS-FAS.
Chronic non-malignant lymphoproliferation. Expansion of antigen-specific lymphocyte populations that are not eliminated through apoptosis leads to expansion of the lymphoid compartment, resulting in lymphadenopathy, splenomegaly, hypersplenism, and, less frequently, hepatomegaly. In most individuals with ALPS-FAS, this finding typically manifests in the first years of life. In some individuals, splenomegaly is the predominant or only manifestation of lymphoproliferation [Bleesing 2003, Rieux-Laucat et al 2003].
The median age of onset was three years in the French cohort and 2.7 years in the NIH cohort. Lymphadenopathy was present in 85% in the French cohort and 97% in the NIH cohort, while splenomegaly was present in 94% in the French cohort (with 73% showing hypersplenism) and 95% in the NIH cohort [Neven et al 2011, Price et al 2014].
In many individuals, lymphadenopathy tends to decrease early in the second decade, whereas splenomegaly often does not. Furthermore, long-term follow up in several individuals has shown that diminution of lymphadenopathy is not accompanied by significant changes in the overall expansion of lymphocyte subsets in peripheral blood [Bleesing et al 2001]. The lymphoproliferation waxes and wanes for reasons that are not entirely clear. Intercurrent viral and bacterial infections can influence lymphadenopathy, perhaps reflecting activation of other (intact) apoptosis pathways.
The overall prognosis of lymphoproliferation is relatively good; few individuals require long-term treatment with immunosuppressive agents to control lymphoproliferation [Bleesing 2003, Rieux-Laucat et al 2003, Neven et al 2011, Price et al 2014].
Laboratory findings of lymphoproliferation show expansion of most lymphocyte subsets including the pathognomonic α/β-DNT cells as well as other T- and B-cell subsets.
Autoimmunity, a common feature of ALPS, is often not present at the time of diagnosis or at the time of the most extensive lymphoproliferation. The reason for the delay in onset is unclear but may be related to age-dependent acquisition of secondary pathogenic factors that interact with defective Fas-mediated apoptosis. In many individuals with ALPS autoantibodies can be detected years before the appearance of clinical manifestations of autoimmune disease [Bleesing 2003, Rieux-Laucat et al 2003].
The French cohort and NIH cohort revealed that, in general, affected individuals with later disease onset often present with autoimmune disease, while younger individuals typically present with lymphoproliferative disease, followed by autoimmune disease, with a two- to three-year delay between lymphoproliferative disease onset and autoimmune disease onset. However, many affected individuals in both age groups presented with autoimmune disease as their first manifestation of ALPS [Neven et al 2011, Price et al 2014].
Although autoimmune manifestations can also wax and wane, current knowledge suggests that autoimmune disease poses a lifelong burden. In the NIH cohort, 37% of affected individuals were described as having a severe autoimmune disease phenotype (as determined by the presence of grade 3 or 4 cytopenias) within two years of disease onset [Price et al 2014].
Autoimmunity most often involves combinations of Coombs-positive hemolytic anemia and immune thrombocytopenia (together referred to as Evans syndrome); autoimmune neutropenia is less common. The observation of primary lymphopenia, contrasting with the typical presence of lymphocytosis, suggests the possibility of autoimmune lymphopenia (as seen in other autoimmune diseases).
The presence of Evans syndrome without significant lymphoproliferation can be consistent with ALPS, especially if α/β-DNT cells are present [Seif et al 2010].
Autoimmune cytopenias may be difficult to distinguish from the effects of concomitant hypersplenism; examination of blood smears for evidence of hemolysis and measurement of autoantibodies and the degree of reticulocytosis may help in establishing the distinction.
Additional autoimmune features can be found, often in patterns that appear to be family specific, suggesting the influence of other (background) genetic information [Rieux-Laucat et al 1999, Vaishnaw et al 1999, Kanegane et al 2003].
Laboratory findings include among others: autoantibodies detected by direct and indirect antiglobulin tests (Coombs' test), antiplatelet antibodies, antineutrophil antibodies, antinuclear antibodies (ANA), and antiphospholipid antibodies.
Lymphoma. Individuals with ALPS-FAS are at an increased risk for both Hodgkin and non-Hodgkin lymphoma, underscoring the role of Fas as a tumor-suppressor gene. Based on calculations in one study, the increased risk is 14-fold and 51-fold for non-Hodgkin lymphoma (NHL) and Hodgkin lymphoma (HL), respectively [Straus et al 2001].
More recently, updated risk calculations were provided through the French cohort and the NIH cohort. The French cohort provided a 15% cumulative risk of lymphoma before age 30 years. This represented seven cases of lymphoma (3 cases of HL and 4 cases of NHL) out of a total of 90 affected individuals [Neven et al 2011].
In the NIH cohort, 18 cases of lymphoma out of a total of 150 affected individuals were identified with a median age of detection of 18 years and a male-to-female ratio of 3.5 to 1. Sixteen (89%) of 18 cases were of B-cell origin. It was determined that 17/18 cases occurred in individuals with pathogenic variants affecting the death domain of FAS. Using published expected cases of HL and NHL in the general population, the 16 cases of B-cell lymphoma conferred a standardized incidence ratio of 149 for HL and 61 for NHL. These numbers are significantly different from those previously published by the NIH group [Straus et al 2001, Price et al 2014].
Lymphoma typically originates in B cells, but has been found in T cells as well, although much less frequently (2/18 cases in the NIH cohort) [Price et al 2014]. Lymphoma is not related to Epstein-Barr virus (EBV) infection (based on absence of EBV in tumor biopsies).
Current experience suggests that lymphomas can occur at any age in ALPS-FAS and do respond to conventional chemotherapeutic treatment. Individuals with other forms of ALPS may also be at an increased risk for lymphoma; however, further data are needed to provide a detailed risk assessment. Because of the frequent concomitant presence of benign (i.e., "typical") lymphadenopathy and splenomegaly, distinguishing a "good" node from a "bad" node is a diagnostic challenge. Important clues are B-type symptoms including fever, night sweats, itching, and weight loss. In addition, PET-based imaging may be helpful in distinguishing "good" from "bad" nodes on the basis of presumed higher metabolic activity of malignant lymphoid tissue [Rao et al 2006].
A number of studies have looked at associations between Fas and neoplasms, including somatic pathogenic variants in solid tumors, leukemias, and lymphomas. For further discussion, see Müschen et al [2002], Houston & O'Connell [2004], Poppema et al [2004], and Peter et al [2005].