All people with ALPS have signs of lymphoproliferation, which makes it the most common clinical manifestation of the disease. The increased proliferation of lymphoid cells can cause the size of lymphoid organs such as the lymph nodes and spleen to increase (lymphadenopathy and splenomegaly, present in respectively over 90% and over 80% of patients). The liver is enlarged (hepatomegaly in 30 - 40% of patients).

Autoimmune disease is the second most common clinical manifestation and one that most often requires treatment. Autoimmune cytopenias: Most common. Can be mild to very severe. Can be intermittent or chronic. These include: Autoimmune hemolytic anemia, Autoimmune neutropenia, Autoimmune thrombocytopenia.

Other signs can affect organ systems similar to systemic lupus erythematosus (least common, affecting <5% of patients) Symptoms of the nervous system include: Autoimmune cerebellar ataxia; Guillain–Barré syndrome; transverse myelitis. Gastrointestinal signs like Autoimmune esophagitis, gastritis, colitis, hepatitis, pancreatitis can be found or (Dermatologic) Urticaria, (Pulmonary) bronchiolitis obliterans, (Renal) Autoimmune glomerulonephritis, nephrotic syndrome.

Another sign are cancers such as Hodgkin and non-Hodgkin lymphomas which appear to be increased, possibly due to Epstein–Barr virus-encoded RNA-positivity. Some carcinomas may occur. Unaffected family members with genetic mutations are also at an increased risk of developing cancer.

Lymphoproliferative disorders (LPDs) refer to several conditions in which lymphocytes are produced in excessive quantities. They typically occur in people who have a compromised immune system. They are sometimes equated with "immunoproliferative disorders", but technically lymphoproliferative disorders are a subset of immunoproliferative disorders, along with hypergammaglobulinemia and paraproteinemias.

Lymphoproliferative disorders are a set of disorders characterized by the abnormal proliferation of lymphocytes into a monoclonal lymphocytosis. The two major types of lymphocytes are B cells and T cells, which are derived from pluripotent hematopoetic stem cells in the bone marrow. Individuals who have some sort of dysfunction with their immune system are susceptible to develop a lymphoproliferative disorder because when any of the numerous control points of the immune system become dysfunctional, immunodeficiency or deregulation of lymphocytes is more likely to occur. There are several inherited gene mutations that have been identified to cause lymphoproliferative disorders; however, there are also acquired and iatrogenic causes.

XMEN patients have splenomegaly, chronic Epstein Barr Virus (EBV) infection, and are developmentally normal. They have an increased susceptibility for developing EBV+ lymphoma. Additionally, XMEN patients have excessive infections consistent with the underlying immunodeficiency. These infections included recurrent otitis media, sinusitis, viral pneumonia, diarrhea, upper respiratory infections, epiglottitis, and pertussis. Although autoimmune symptoms do not feature prominently in XMEN autoimmune cytopenias were observed in two unrelated patients.

In the figure to the left, major features are present in all XMEN patients, while minor features are found only in some.

Clinically, RALD is characterized by splenomegaly, a relatively mild degree of peripheral lymphadenopathy, and autoimmunity. The autoimmune phenotype can present in childhood or adulthood and primarily includes autoimmune hemolytic anemia, ITP, and neutropenia. Some patients have a history of recurrent respiratory tract infections. It is unclear if increased risk for malignancy is part of RALD.

Importantly, however, the clinical and laboratory phenotype resembles juvenile myelomonocytic leukemia. The high fatality rate of this childhood blood cancer puts it in sharp contrast when compared to the relatively benign and chronic course of RALD. Approximately 15-30% of patients diagnosed with JMML have somatic, activating RAS mutations. However, due to the difficulty in distinguishing JMML from RALD, it is possible a subset of patients treated for JMML actually have RALD and could therefore avoid the aggressive JMML treatment. This distinction is under investigation.

RAS-associated autoimmune leukoproliferative disorder (RALD) is a rare genetic disorder of the immune system. RALD is characterized by lymphadenopathy, splenomegaly, autoimmunity, and elevation in granulocytes and monocytes. It shares many features with autoimmune lymphoproliferative syndrome and is caused by somatic mutations in NRAS or KRAS. This was first described by investigators João Oliveira and Michael Lenardo from the National Institutes of Health.

Post-transplant lymphoproliferative disorder (PTLD) is the name given to a B-cell proliferation due to therapeutic immunosuppression after organ transplantation. These patients may develop infectious mononucleosis-like lesions or polyclonal polymorphic B-cell hyperplasia. Some of these B-cells may undergo mutations which will render them malignant, giving rise to a lymphoma.

In some patients, the malignant cell clone can become the dominant proliferating cell type, leading to frank lymphoma, a group of B cell lymphomas occurring in immunosuppressed patients following organ transplant.

Individuals with BENTA disease have polyclonal B cell lymphocytosis (i.e. excess B cells) developing in infancy, in addition to splenomegaly and lymphadenopathy. Patients may have low serum IgM and mildly anergic T cells. These features likely contribute to the mild immunodeficiency seen with BENTA disease. Patients are generally susceptible to recurrent sinopulmonary and ear infections in childhood, and may be more susceptible to certain viruses including Epstein-Barr virus, BK virus, and molluscum contagiosum.

XMEN disease is a rare genetic disorder of the immune system that illustrates the role of Mg2+ in cell signaling. XMEN stands for “X-linked immunodeficiency with magnesium defect, Epstein-Barr virus (EBV) infection, and neoplasia.” It is characterized by CD4 lymphopenia, severe chronic viral infections, and defective T-lymphocyte activation. Investigators in the laboratory of Dr. Michael Lenardo, National Institute of Allergy and Infectious Diseases at the National Institutes of Health first described this condition in 2011.

This disease is known for an indolent clinical course and incidental discovery. The most common physical finding is moderate splenomegaly. B symptoms are seen in a third of cases, and recurrent infections due to the associated neutropenia are seen in almost half of cases.

Rheumatoid arthritis is commonly observed in people with T-LGLL, leading to a clinical presentation similar to Felty's syndrome. Signs and symptoms of anemia are commonly found, due to the association between T-LGLL and erythroid hypoplasia.

Patients with this disease usually present at an advanced stage and show systemic involvement. The clinical findings typically include a pruritic skin rash and possibly edema, ascites, pleural effusions, and arthritis.

Autoimmune lymphoproliferative syndrome (ALPS), also known as Canale-Smith syndrome, is a form of lymphoproliferative disorder (LPDs). It affects lymphocyte apoptosis. It is a RASopathy.

It is a rare genetic disorder of abnormal lymphocyte survival caused by defective Fas mediated apoptosis. Normally, after infectious insult, the immune system down-regulates by increasing Fas expression on activated B and T lymphocytes and Fas-ligand on activated T lymphocytes. Fas and Fas-ligand interact to trigger the caspase cascade, leading to cell apoptosis. Patients with ALPS have a defect in this apoptotic pathway, leading to chronic non-malignant lymphoproliferation, autoimmune disease, and secondary cancers.

BENTA disease is a rare genetic disorder of the immune system. BENTA stands for "B cell expansion with NF-κB and T cell anergy" and is caused by germline heterozygous gain-of-function mutations in the gene CARD11 (see OMIM entry #607210). This disorder is characterized by polyclonal B cell lymphocytosis with onset in infancy, splenomegaly, lymphadenopathy, mild immunodeficiency, and increased risk of lymphoma. Investigators Andrew L. Snow and Michael J. Lenardo at the National Institute of Allergy and Infectious Disease at the U.S. National Institutes of Health first characterized BENTA disease in 2012. Dr. Snow's current laboratory at the Uniformed Services University of the Health Sciences is now actively studying this disorder.

The leukemic cells of T-LGLL can be found in peripheral blood, bone marrow, spleen, and liver. Nodal involvement is rare.

Due to the systemic nature of this disease, neoplastic cells can be found in lymph nodes, liver, spleen, skin, and bone marrow.

Immunoproliferative disorders, also known as immunoproliferative diseases or immunoproliferative neoplasms, are disorders of the immune system that are characterized by the abnormal proliferation of the primary cells of the immune system, which includes B cells, T cells and natural killer (NK) cells, or by the excessive production of immunoglobulins (also known as antibodies).

The disease is believed to be induced by a combination of Epstein Barr virus infection and immunosuppression through; immunosuppressive drugs (with case reports of methotrexate and azathioprine), infections such as HIV or chronic viral hepatitis or endogenous T-cell defects.

Lymphomatoid granulomatosis (LYG or LG) is a very rare lymphoproliferative disorder first characterized in 1972 with lymphomatoid meaning lymphoma-like and granulomatosis denoting one of its microscopic characteristics, polymorphic lymphoid infiltrates and focal necrosis within it. While most commonly found in middle age patients, it has been observed in young people with a study identifying 47 cases of patients aged 0–18 years in the literature. Males are found to be affected twice as often as females.

PASLI disease is a rare genetic disorder of the immune system. PASLI stands for “p110 delta activating mutation causing senescent T cells, lymphadenopathy, and immunodeficiency.” The immunodeficiency manifests as recurrent infections usually starting in childhood. These include bacterial infections of the respiratory system and chronic viremia due to Epstein-Barr virus (EBV) and/or cytomegalovirus (CMV). Individuals with PASLI disease also have an increased risk of EBV-associated lymphoma. Investigators Carrie Lucas, Michael Lenardo, and Gulbu Uzel at the National Institute of Allergy and Infectious Diseases at the U.S. National Institutes of Health and Sergey Nejentsev at the University of Cambridge, UK simultaneously described a mutation causing this condition which they called Activated PI3K Delta Syndrome (APDS).

These disorders are subdivided into three main classes, which are lymphoproliferative disorders, hypergammaglobulinemia, and paraproteinemia. The first is cellular, and the other two are humoral (however, humoral excess can be secondary to cellular excess.)

- "Lymphoproliferative disorders" (LPDs) refer to several conditions in which lymphocytes are produced in excessive quantities. They typically occur in patients who have compromised immune systems. This subset is sometimes incorrectly equated with "immunoproliferative disorders".

- Humoral

- "Hypergammaglobulinemia" is characterized by increased levels of immunoglobulins in the blood serum. Five different hypergammaglobulinemias are caused by an excess of immunoglobulin M (IgM), and some types are caused by a deficiency in the other major types of immunoglobulins.

- "Paraproteinemia" or "monoclonal gammopathy" is the presence of excessive amounts of a single monoclonal gammaglobulin (called a "paraprotein") in the blood.

Patients usually present with constitutional symptoms (malaise, weight loss, fatigue), and hepatosplenomegaly is commonly found on physical exam. Lymphadenopathy is also found to a lesser extent. Due to the aggressive nature of the disease, patients may initially present at a more advanced stage, with coagulopathies, hemophagocytic syndrome, and multi-organ failure.

The onset of HLH occurs under the age of 1 year in ~70% of cases. Familial HLH should be suspected if siblings are diagnosed with HLH or if symptoms recur when therapy has been stopped. Each full sibling of a child with familial HLH has a 25% chance of developing the disease, a 50% chance of carrying the defective gene (which is very rarely associated with any risk of disease) and a 25% chance of not being affected and not carrying the gene defect.

Patients with HLH, especially when untreated, may need intensive therapy. Therefore, HLH should be included in the differential diagnosis of ICU (Intensive Care Unit) patients with cytopenia and hyperferritinemia.

HLH clinically manifests with fever, enlargement of the liver and spleen, enlarged lymph nodes, yellow discoloration of the skin and eyes, and a rash.

Clinically, PASLI disease is characterized by recurrent sinopulmonary infections that can lead to progressive airway damage. Patients also suffer from lymphoproliferation (large lymph nodes and spleen), chronic viremia due to EBV or CMV, distinctive lymphoid nodules at mucosal surfaces, autoimmune cytopenias, and EBV-driven B cell lymphoma. Importantly, the clinical presentations and disease courses are variable with some individuals severely affected, whereas others show little manifestation of disease. This “variable expressivity,” even within the same family, can be striking and may be explained by differences in lifestyle, exposure to pathogens, treatment efficacy, or other genetic modifiers.

Strangely, in boys with X-linked lymphoproliferative disorder, there is an inability to mount an immune response to the Epstein-Barr virus (EBV), which often leads to death from bone marrow failure, irreversible hepatitis, and malignant lymphoma. However, the connection between EBV and X-linked lymphoproliferative disorder is yet to be determined.

Patients produce insufficient numbers of CD27 memory B cells.

The precise symptoms of a primary immunodeficiency depend on the type of defect. Generally, the symptoms and signs that lead to the diagnosis of an immunodeficiency include recurrent or persistent infections or developmental delay as a result of infection. Particular organ problems (e.g. diseases involving the skin, heart, facial development and skeletal system) may be present in certain conditions. Others predispose to autoimmune disease, where the immune system attacks the body's own tissues, or tumours (sometimes specific forms of cancer, such as lymphoma). The nature of the infections, as well as the additional features, may provide clues as to the exact nature of the immune defect.