What Is Autoimmune Lymphoproliferative Syndrome (ALPS)?

Autoimmune lymphoproliferative syndrome, known as ALPS, is a rare inherited disorder in which the body’s immune cells fail to die on schedule, leading to a buildup of lymphocytes that causes chronically swollen lymph nodes, an enlarged spleen, and a tendency for the immune system to attack the body’s own blood cells. Most cases trace back to mutations in a single gene called FAS, which normally triggers a self-destruct signal in immune cells that have outlived their usefulness. The condition typically shows up in childhood, and while it can range from barely noticeable to life-threatening, understanding the underlying defect has opened the door to targeted treatments that work remarkably well.

Why Immune Cells Need to Self-Destruct

Your immune system generates enormous numbers of lymphocytes every day to fight infection. Once a threat is handled, most of those cells need to be cleared away. The main off-switch for this process is a protein called FAS, which sits on the surface of lymphocytes and, when activated, triggers a form of programmed cell death. FAS acts as a guardian against both autoimmunity and tumor development by eliminating lymphocytes that are no longer needed or that have started reacting against the body’s own tissues.¹

When FAS signaling is broken, those obsolete and self-reactive lymphocytes survive instead of dying. They pile up in the lymph nodes and spleen, and some of the surviving cells produce antibodies directed against the person’s own red blood cells, platelets, or white blood cells. That, in a nutshell, is ALPS: a failure to clean house, with consequences that ripple through the entire blood and immune system.²

The Genetics Behind ALPS

The most common genetic cause is a harmful mutation in the FAS gene itself, a subtype formally called ALPS-FAS. These are typically heterozygous mutations, meaning a person only needs one defective copy of the gene (inherited from one parent) to develop the condition.³ But a FAS mutation alone does not guarantee severe disease. In some families, the same mutation produces wildly different outcomes: one carrier might have life-threatening blood cell destruction in infancy, while a grandparent carrying the identical mutation had only mildly low platelet counts and went decades without a diagnosis.⁴

Not every patient inherits the mutation from a parent. Research has shown that more than a third of patients who were previously classified as having no known genetic cause actually carry somatic FAS mutations, meaning the mutation arose spontaneously in a subset of their cells after conception rather than being present in every cell from birth. These somatic mutations tend to cluster in the part of the FAS protein responsible for sending the death signal inside the cell, and they produce the same immune abnormalities seen in patients with inherited mutations.⁵

A smaller number of patients have mutations in other genes within the same cell-death pathway, and some remain genetically undefined despite testing. Broadly, though, ALPS centers on a broken apoptotic signal, and FAS is the gene at fault in the overwhelming majority of cases.

What ALPS Looks Like

ALPS usually makes itself known in early childhood, though the severity varies enormously. The three hallmark features are chronic, non-cancerous swelling of the lymph nodes, an enlarged spleen, and low blood cell counts caused by the immune system attacking its own blood cells.⁶ In a large systematic review of nearly 780 patients, splenomegaly was the single most common presentation, followed by autoimmune cytopenias and lymphadenopathy.⁷

The lymph node swelling can be dramatic. Children sometimes present with visibly enlarged nodes in the neck, armpits, and groin that persist for months or years, raising understandable fears of lymphoma. These nodes are benign, but distinguishing them from malignancy is one of the diagnostic challenges. Splenomegaly can be severe enough to cause discomfort, early satiety, and physical activity restrictions.

Autoimmune Blood Cell Destruction

The autoimmune component of ALPS most often targets blood cells. The three common forms are autoimmune hemolytic anemia (the immune system destroys red blood cells), immune thrombocytopenia (platelets are destroyed, raising bleeding risk), and autoimmune neutropenia (white blood cells called neutrophils are targeted, raising infection risk). These can occur alone or in combination, and they can be the most dangerous aspect of the disease when they are severe.⁸ Making things more complicated, low blood counts in ALPS are not always autoimmune in origin. The massively enlarged spleen can trap and destroy blood cells on its own through a process called splenic sequestration, so a patient’s anemia or low platelets may reflect a mix of both mechanisms.

Beyond Blood Cells

While cytopenias dominate the autoimmune picture, some patients develop autoimmune problems affecting other organs, including arthritis and colitis. These are less common than the blood-cell problems but can be just as debilitating when they occur.

How ALPS Is Diagnosed

The diagnostic process relies on a combination of clinical findings, a specific immune cell marker, and a panel of blood biomarkers. Revised international criteria published in 2009 formalized the requirements, building on roughly 500 patients studied worldwide up to that point.⁹

The Double-Negative T Cell

The immunological hallmark of ALPS is an unusual population of mature T cells that lack both the CD4 and CD8 markers normally found on T cells. These “double-negative” T cells (DNTs) are rare in healthy people but accumulate in ALPS patients because they survive when they should not.¹⁰ An elevated percentage of DNTs in the blood is one of the required findings for a formal ALPS diagnosis. In some patients, DNTs can make up a striking proportion of the total lymphocyte population.

Blood Biomarkers That Point Toward ALPS

Beyond DNT cells, several blood tests help clinicians decide whether to pursue genetic testing for FAS mutations. Vitamin B12 levels, soluble FAS ligand, and interleukin-10 are consistently elevated in ALPS and serve as useful screening tools. One study found that combining vitamin B12 and soluble FAS ligand levels (using specific cutoff values) predicted FAS mutations with a positive predictive value of 92% and a negative predictive value of 97%, which is unusually accurate for a screening combination.¹¹ These biomarkers led researchers to build a web-based probability calculator that helps clinicians decide whether genetic sequencing is warranted for a given patient.

Additional markers including interleukin-18 and TNF-alpha are also elevated in ALPS patients compared to healthy controls. When DNTs are above 4% and one of the key biomarkers (interleukin-10, vitamin B12, or soluble FAS ligand) is above its threshold, the probability of finding a FAS mutation reaches roughly 97%.¹² This matters because it lets clinicians avoid unnecessary invasive procedures and move directly toward the right genetic test.

The Lymphoma Question

One of the most worrying aspects of ALPS is a raised risk for lymphoma, both Hodgkin and non-Hodgkin types. The increased risk is well documented across multiple reviews of ALPS patients.¹³ The paradox is intuitive once you understand the mechanism: when lymphocytes escape their normal death signals, they survive longer and accumulate more genetic damage over time, creating a fertile ground for malignant transformation.

This is part of what makes ALPS more than just a nuisance of swollen glands. Even patients whose day-to-day symptoms are manageable need ongoing surveillance, because the same defect that allows benign lymphocyte buildup also creates conditions for cancerous ones. The lymphoma risk is one reason aggressive monitoring and appropriate treatment matter, even in patients who feel well.

Treatment Approaches

Managing ALPS has shifted considerably over the past two decades, moving away from blunt immune suppression toward more targeted strategies.

Corticosteroids and Mycophenolate

Corticosteroids remain the first-line treatment when autoimmune cytopenias flare, particularly for acute hemolytic anemia or dangerously low platelet counts. The problem is that steroids come with well-known long-term side effects, and many ALPS patients need ongoing treatment, making steroids a poor chronic solution. Mycophenolate mofetil (MMF) has been used as a steroid-sparing option, particularly for patients with chronic, refractory thrombocytopenia. In one large cohort, 40 out of 245 ALPS patients received MMF for this purpose, and it was generally well tolerated as a long-term measure.¹⁴

Sirolimus as a Game-Changer

The introduction of sirolimus (also known as rapamycin) has been one of the most significant advances in ALPS treatment. Sirolimus works by blocking a protein called mTOR that drives cell growth and proliferation, and it turns out to be almost uniquely effective in ALPS. In an initial series of patients who had failed steroids and other immune-suppressing drugs, three out of four treated for autoimmune cytopenias had complete resolution of their blood cell destruction, and the fourth had near-complete resolution. All four were completely off steroids within a month of starting sirolimus. Among patients with lymph node and spleen enlargement, three out of five had a complete response. Perhaps most remarkably, the abnormal DNT cells that define the disease dropped by more than 50% in five of six patients.¹⁵

Larger prospective trials confirmed these findings. In one multi-center study, all 12 children with ALPS who received sirolimus achieved a durable complete response, with rapid improvement in autoimmune disease, lymphadenopathy, and splenomegaly within one to three months. The double-negative T cells became undetectable in most patients, yet other lymphocyte populations were spared, suggesting that sirolimus has a remarkably targeted effect on the abnormal cells driving the disease rather than broadly suppressing the immune system.¹⁶ A separate study of 22 patients demonstrated that sirolimus was effective even at reduced doses, and that treatment normalized not just symptoms but also biomarkers like vitamin B12 and DNT cell counts.¹⁷

Sirolimus does need to be taken continuously, and it carries its own side effects (mouth sores, elevated cholesterol, and increased infection risk, among others), but the degree of disease control it offers is unusual for a rare disease treatment. For many families, sirolimus has transformed ALPS from a condition requiring frequent hospitalizations and steroid courses into something manageable with a daily medication.

Why Splenectomy Is a Bad Idea

Given how large the spleen can get in ALPS, and given how commonly splenectomy is performed for other causes of immune-mediated blood cell destruction, it might seem logical to remove the spleen. In ALPS, though, this approach has fallen out of favor for good reason. Experts at the National Institutes of Health have explicitly warned against splenectomy in ALPS-FAS, arguing that the spleen, however enlarged, plays an ongoing role in immune surveillance that these patients can ill afford to lose.¹⁸ Removing the spleen in ALPS patients raises the already elevated lymphoma risk and leaves patients more vulnerable to certain bacterial infections for life. The same guidance warns against rituximab, a drug that depletes B cells, for similar reasons. Despite these warnings, cases of unnecessary splenectomy in young ALPS patients have continued to occur, underscoring the importance of recognizing the diagnosis before resorting to surgery.

Variable Penetrance Within Families

One of the more puzzling features of ALPS is how different it can look within a single family carrying the same mutation. A case report illustrating this dramatically described an infant who presented before birth with hydrops fetalis (severe fluid accumulation), hepatosplenomegaly, and anemia caused by a novel FAS mutation. The baby’s father and paternal grandmother carried the identical mutation but had experienced only mild autoimmune cytopenias and elevated DNT cells, nothing close to the severity seen in the infant.¹⁹

This variable penetrance means that a positive genetic test in one family member does not predict how sick another carrier will become. It also complicates genetic counseling. A parent with a known FAS mutation may have lived a nearly normal life and be surprised to learn their child could develop severe disease. The factors that push one carrier toward severe disease and another toward mild or no symptoms are not fully understood, though modifier genes, environmental triggers, and the specific location of the mutation within the FAS protein all likely play a role.

ALPS-Like Conditions and Mimics

Not everything that looks like ALPS actually is. Several other genetic immune disorders produce overlapping features: chronic lymph node swelling, splenomegaly, autoimmune cytopenias, and even elevated DNT cells to varying degrees. These are sometimes grouped under the umbrella of “ALPS-like” syndromes, and distinguishing them matters because the treatments and long-term risks can differ.

Two of the better-characterized mimics involve deficiencies in immune checkpoint proteins: CTLA-4 insufficiency and LRBA deficiency. Both can present with lymphoproliferation and autoimmune cytopenias that look clinically similar to ALPS, but they arise from entirely different genetic and biological defects.²⁰ Patients with CTLA-4 insufficiency, for instance, often have more prominent organ-specific autoimmune problems (such as lung or gut inflammation) and may respond to a different targeted therapy called abatacept that replaces the missing CTLA-4 function. Getting the genetics right matters for choosing the right treatment, not just for academic classification.

Evans syndrome, a condition in which a person develops autoimmune destruction of both red blood cells and platelets, is another common clinical overlap. In some pediatric series, a subset of children initially diagnosed with Evans syndrome were eventually found to have an underlying genetic immune disorder, including ALPS. This has led to growing awareness that children with unexplained, recurrent autoimmune cytopenias deserve evaluation for ALPS and related genetic conditions rather than simply being treated symptomatically with steroids and transfusions each time a flare occurs.

Living With ALPS Across the Lifespan

Although ALPS typically presents in childhood, it does not simply resolve with age. The lymphoproliferation often improves somewhat during adolescence and adulthood, with lymph nodes becoming less dramatically enlarged, but the autoimmune cytopenias and the lymphoma risk persist. Patients who are on long-term sirolimus generally need to continue the medication, and all patients require regular monitoring with blood counts and imaging to watch for signs of malignancy.

For families, receiving an ALPS diagnosis can be both alarming and oddly reassuring. Many patients have spent years being shuttled between specialists, undergoing repeated biopsies of enlarged lymph nodes to rule out cancer, and enduring courses of steroids with no lasting benefit. A definitive genetic diagnosis provides an explanation for years of confusing symptoms and opens the door to targeted therapy. Genetic testing of relatives can identify carriers who may benefit from monitoring even if they are currently asymptomatic, given the variable penetrance discussed earlier. The rarity of the condition means that many general practitioners and even some hematologists have never encountered a case, so finding a center with ALPS experience can make a significant difference in the quality of care a patient receives.