Laboratory Findings

Although no specific laboratory abnormality alone is diagnostic of ALPS, the detection of the following facilitates the diagnosis [Bleesing 2003, Magerus-Chatinet et al 2009, Caminha et al 2010, Oliveira et al 2010, Rensing-Ehl et al 2013]:

• Defective Fas-mediated apoptosis in vitro
• T cells that express the alpha/beta T-cell receptor but lack both CD4 and CD8 (so-called alpha/beta double-negative T cells [α/β-DNT cells] in peripheral blood or tissue specimens). Detected by flow cytometric immunophenotyping, these terminally differentiated in vivo-activated T cells are rare in healthy individuals and other immune-mediated (lymphoproliferative) disorders; typically they constitute less than 2% of the lymphocyte pool.
• Increased levels of the ALPS-specific biomarkers: soluble IL-10, IL-18, FasL, and vitamin B₁₂ in plasma/serum [Bowen et al 2012]

Secondary laboratory findings in ALPS [Lim et al 1998, Carter et al 2000, Bleesing et al 2001,Bleesing 2003, Bleesing 2005, Maric et al 2005, Magerus-Chatinet et al 2009, Caminha et al 2010, Oliveira et al 2010, Bowen et al 2012, Neven et al 2014]:

• Hematology
  • Lymphocytosis, lymphopenia (primary or secondary in response to treatment)
  • Coombs-positive hemolytic anemia
  • Dyserythropoiesis
  • Reticulocytosis
  • Thrombocytopenia
  • Neutropenia
  • Eosinophilia
• Immunology
  • Expansion of other lymphocyte subsets
    • Gamma/delta-DNT cells
    • CD8+/CD57+ T cells
    • HLA-DR+ T cells
    • CD5+ B cells
  • Decreased numbers of CD4+/CD25+ T cells
  • Decreased numbers of CD27+ B cells
  • Elevated concentration of IL-10 and IL-18 in serum/plasma
  • Elevated concentrations of IgG, IgA, and IgE; normal or decreased concentrations of IgM
  • Autoantibodies (most often positive direct or indirect antiglobulin test, antiplatelet antibody, antineutrophil antibody, antiphospholipid antibody, antinuclear antibody, rheumatoid factor)
  • Lymph node pathology (paracortical expansion with immunoblasts/plasma cells and DNT cells in interfollicular areas, florid follicular hyperplasia, progressive transformation of germinal centers [PTGC])
• Other
  • Increased soluble CD25 (sIL-2R alpha), CD27, CD30, and Fas ligand (FasL)
  • Monoclonal gammopathy
  • Decreased antibody responses to polysaccharide antigens [Neven et al 2014]
• Chemistry
  • Liver function abnormalities (in case of autoimmune hepatitis)
  • Proteinuria (in case of glomerulonephritis)
  • Elevated serum concentration of vitamin B₁₂

Normal findings in (typical) ALPS

• Neutrophil function
• Complement factors concentrations and function
• In vitro proliferative responses of T cells (e.g., in response to common mitogens and antigens)
• NK-cell and cytotoxic T-lymphocyte (CTL) function; possibly decreased CTL activity in ALPS on the basis of defective FasL (i.e., ALPS-FASLG).
• Antibody responses to protein antigens (e.g., diphtheria, tetanus)

Note: (1) The abnormal and normal laboratory findings listed have been most reliably established for individuals with ALPS caused by either germline or somatic pathogenic variants in FAS. (2) Cell surface expression of Fas (CD95) can be normal, increased, or decreased and is in general not helpful in the diagnosis of ALPS. (3) When interpreting laboratory data of individuals with (suspected) ALPS, the influence of concurrent immunosuppressive agents at the time of testing needs to be considered.

Molecular Genetic Testing

Molecular genetic testing approaches can include serial single-gene testing, use of a multigene panel, and more comprehensive genomic testing.

Serial single-gene testing. Sequence analysis of the gene of interest is performed first and followed by gene-targeted deletion/duplication analysis if no pathogenic variant is found.

• For this disorder, it is recommended that FAS be tested first. See Figure 1 for algorithm.
• In the absence of a germline FAS pathogenic variant, FAS sequencing in sorted α/β-DNT cells to detect somatic pathogenic variants should be performed. If present, the diagnosis of ALPS-sFAS is established.
• If neither a germline nor a somatic FAS pathogenic variant is identified, CASP10 and FASLG should be tested next. The detection of germline pathogenic variants in either CASP10 or FASLG establishes the diagnosis of ALPS-CASP10 or ALPS-FASLG, respectively.
• A Fas-mediated apoptosis assay should be performed if germline pathogenic variants in CASP10 or FASLG are not identified (repeat if necessary, noting the influence of concomitant immunosuppressive therapy). If abnormal, the diagnosis of ALPS-U is established.

Figure 1.

One proposed algorithm for the diagnostic evaluation of an individual suspected of having ALPS

Notes: (1) Absence of a positive family history is suggestive of ALPS-sFAS. (2) Loss of heterozygosity of FAS pathogenic variants has been observed in blood cells. (3) FAS somatic pathogenic variants in selected cell populations, including α/β-DNT cells, produce a phenotype similar to that caused by FAS germline pathogenic variants. (4) The presence of elevated biomarkers has not been reliably established in CASP10 or FASLG-related ALPS. (5) Thus far, somatic pathogenic variants in FAS only have been reported to cause ALPS; however, it is theoretically possible that somatic pathogenic variants in CASP10 and FASLG may also be causative.

A multigene panel that includes CASP10, FAS, FASLG, and other genes of interest (see Differential Diagnosis) may also be considered. Note: (1) The genes included in the panel and the diagnostic sensitivity of the testing used for each gene vary by laboratory and are likely to change over time. (2) Some multigene panels may include genes not associated with the condition discussed in this GeneReview; thus, clinicians need to determine which multigene panel is most likely to identify the genetic cause of the condition at the most reasonable cost while limiting identification of variants of uncertain significance and pathogenic variants in genes that do not explain the underlying phenotype. (3) In some laboratories, panel options may include a custom laboratory-designed panel and/or custom phenotype-focused exome analysis that includes genes specified by the clinician. (4) Methods used in a panel may include sequence analysis, deletion/duplication analysis, and/or other non-sequencing-based tests.

For an introduction to multigene panels click here. More detailed information for clinicians ordering genetic tests can be found here.

More comprehensive genomic testing (when available) including exome sequencing and genome sequencing may be considered. Such testing may provide or suggest a diagnosis not previously considered (e.g., mutation of a different gene or genes that results in a similar clinical presentation).

For an introduction to comprehensive genomic testing click here. More detailed information for clinicians ordering genomic testing can be found here.

Summary of Clinical Manifestations of ALPS

Lymphoproliferation of non-malignant lymphoid cells

• Lymphadenopathy
• Splenomegaly (+/- hypersplenism)
• Hepatomegaly

Autoimmunity

• Autoimmune hemolytic anemia
• Autoimmune thrombocytopenia
• Autoimmune neutropenia
• Glomerulonephritis
• Autoimmune hepatitis
• Guillain Barré syndrome
• Uveitis, iridocyclitis
• Other autoimmune disorders (in individual cases)

Neoplasia (including benign tumors)

• Lymphoma (Hodgkin and non-Hodgkin lymphoma)
• Carcinoma (thyroid, breast, skin, tongue, liver)
• Multiple neoplastic lesions (thyroid/breast adenomas, gliomas)

Other and/or infrequent findings

• Urticaria and other skin rashes
• Vasculitis
• Panniculitis
• Arthritis and arthralgia
• Recurrent oral ulcers
• Humoral immunodeficiency
• Pulmonary infiltrates
• Premature ovarian insufficiency
• Hydrops fetalis
• Organic brain syndrome (mental status changes, seizures, headaches)

The natural history of ALPS is not well understood. While non-malignant lymphoproliferative manifestations often regress or improve over time, autoimmunity appears to show no permanent remission with advancing age. Moreover, the risk for development of lymphoma likely is lifelong. Thus, in the absence of curative treatment, the overall prognosis for ALPS remains guarded, necessitating long-term clinical studies to better understand its natural history. Two publications have provided significant new insights into the features, complications, natural history, and prognosis of ALPS. These studies are subsequently referred to in this GeneReview as the "French cohort" and the "NIH cohort" [Neven et al 2011, Price et al 2014].

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].

ALPS-FAS Caused by Biallelic Pathogenic Variants

Chronic non-malignant lymphoproliferation. Individuals with homozygous or compound heterozygous FAS pathogenic variants often present with severe lymphoproliferation at or shortly after birth [Rieux-Laucat et al 1995, Le Deist et al 1996, Kasahara et al 1998, van der Burg et al 2000].

Autoimmunity. In several individuals reported, the delay between onset of autoimmunity and lymphoproliferation was minimal, while in others this was not the case. The rarity of and poor prognosis in ALPS-FAS resulting from biallelic pathogenic variants make it difficult to draw firm conclusions regarding autoimmunity in this type of ALPS [Rieux-Laucat et al 1995, Le Deist et al 1996, Kasahara et al 1998, van der Burg et al 2000].

Lymphoma. Because of the severity of ALPS-FAS caused by biallelic pathogenic variants, affected individuals typically succumb to lymphoproliferation and/or autoimmunity at an early age.

ALPS-sFAS

Somatic FAS pathogenic variants in selected cell populations (notably the α/β-DNT cells) have been identified in individuals with ALPS-sFAS. Individuals with somatic FAS pathogenic variants now constitute the second largest group of ALPS. Most of the clinical and laboratory features of ALPS-FAS are recapitulated in individuals with somatic FAS pathogenic variants including age of presentation, although lower incidence of splenectomy and lower lymphocyte counts have been reported in ALPS-sFAS and no cases of lymphoma have yet been published.

The population of α/β-DNT cells is expanded; however, as noted initially [Holzelova et al 2004, Rössler et al 2005, Magerus-Chatinet et al 2011], Fas-mediated apoptosis in vitro is typically not defective, although defective Fas-mediated apoptosis has been noted in some recently published cases [Dowdell et al 2010].

Pathogenesis of ALPS

The phenotype of ALPS results from defective apoptosis of lymphocytes mediated through the Fas/Fas ligand (FasL) pathway. This pathway normally limits the size of the lymphocyte compartment by eliminating/removing autoreactive lymphocytes; therefore, defects in this pathway lead to expansion of antigen-specific lymphocyte populations. Although Fas also appears to play a role in suppression of malignant transformation of lymphocytes, it remains to be firmly established whether this involves the Fas/FasL pathway in a similar way. It should be noted that the pathogenesis of ALPS remains an ongoing topic of research.

Somatic FAS pathogenic variants are of particular interest in understanding the pathogenesis of ALPS, for example, with regard to the observed delay between lymphoproliferation and autoimmunity: the somatic pathogenic variant is mostly confined to the α/β-DNT cells and typically not found (at least not in large proportion) in other lymphocyte subsets such as B cells. Perhaps this observation will help to characterize the impact of the FAS pathogenic variant relative to other potential pathogenic factors.