A 2009 study reported results from 36 children who had received a stem cell transplant. At the time of follow-up (median time 62 months), 75% of the children were still alive.

A survey of 10,000 American households revealed that the prevalence of diagnosed primary immunodeficiency approaches 1 in 1200. This figure does not take into account people with mild immune system defects who have not received a formal diagnosis.

Milder forms of primary immunodeficiency, such as selective immunoglobulin A deficiency, are fairly common, with random groups of people (such as otherwise healthy blood donors) having a rate of 1:600. Other disorders are distinctly more uncommon, with incidences between 1:100,000 and 1:2,000,000 being reported.

The estimated incidence of Wiskott–Aldrich syndrome in the United States is one in 250,000 live male births. No geographical factor is present.

By definition, primary immune deficiencies are due to genetic causes. They may result from a single genetic defect, but most are multifactorial. They may be caused by recessive or dominant inheritance. Some are latent, and require a certain environmental trigger to become manifest, like the presence in the environment of a reactive allergen. Other problems become apparent due to aging of bodily and cellular maintenance processes.

LAD is a rare disease, with an estimated prevalence of one in 100,000 births, with no described racial or ethnic predilection. The most common type is LAD1.

Genetically speaking, Nezelof syndrome is autosomal recessive. the condition is thought to be a variation of severe combined immunodeficiency(SCID) However, the precise cause of Nezelof syndrome remains uncertain

Prevalence varies by population, but is on the order of 1 in 100 to 1 in 1000 people, making it relatively common for a genetic disease.

SigAD occurs in 1 of 39 to 57 patients with celiac disease. This is much higher than the prevalence of selective IgA deficiency in the general population. It is also significantly more common in those with type 1 diabetes.

It is more common in males than in females.

In the mechanism of this condition, one first finds that the normal function of the thymus has it being important in T-cell development and release into the body's blood circulation Hassal's corpusclesabsence in thymus(atrophy) has an effect on T-cells.

Prognosis is excellent, although there is an association with autoimmune disease. Of note, selective IgA deficiency can complicate the diagnosis of one such condition, celiac disease, as the deficiency masks the high levels of certain IgA antibodies usually seen in celiac disease.

As opposed to the related condition CVID, selective IgA deficiency is not associated with an increased risk of cancer.

Patients with Selective IgA deficiency are at risk of anaphylaxis from blood transfusions. These patients should receive IgA free containing blood products and ideally blood from IgA-deficient donors.

No cure currently exists; however, gene therapy has been proposed.

Current research is aimed at studying large cohorts of people with CVID in an attempt to better understand age of onset, as well as mechanism, genetic factors, and progression of the disease.

Funding for research in the US is provided by the National Institutes of Health. Key research in the UK was previously funded by the Primary Immunodeficiency Association (PiA) until its closure in January 2012, and funding is raised through the annual Jeans for Genes campaign. Current efforts are aimed at studying the following:

- Causes of complications. Little is known about why such diverse complications arise during treatment

- Underlying genetic factors. Though many polymorphisms and mutations have been identified, their respective roles in CVID development are poorly understood, and not represented in all people with CVID.

- Finding new ways to study CVID. Given that CVID arises from more than one gene, gene knock-out methods are unlikely to be helpful. It is necessary to seek out disease related polymorphisms by screening large populations of people with CVID, but this is challenging given the rarity of the disease.

ZAP70 deficiency, or zeta-chain-associated protein 70 kD deficiency, is a rare autosomal recessive form of severe combined immunodeficiency (SCID).

It is associated with ZAP70.

Patients with CHH usually suffer from cellular immunodeficiency. In the study of 108 Finnish patients with CHH there was detected mild to moderate form of lymphopenia, decreased delayed type of hypersensitivity and impaired responses to phytohaemagglutinin. This leads to susceptibility to and, in some more severe cases, mortality from infections early in childhood. There has also been detected combined immunodeficiency in some patients

Patients with CHH often have increased predispositions to malignancies.

Tricho-hepato-enteric syndrome is estimated to affect 1 in 300,000 to 400,000 live births in Western Europe. This syndrome was first reported in 1982 with a report on 2 siblings, and as of 2008 there were around 25 published cases in medical journals. There seem to be no racial differences in its occurrence. It might be more common, as many genetic diseases, in areas with high levels of consanguinity.

There is no known cure at the moment but there are several things that can be done to relieve the symptoms. Moisturising products are very helpful to minimize the scaling/cracking, and anti-infective treatments are useful when appropriate because the skin is very susceptible to infection. Extra protein in the diet during childhood is also beneficial, to replace that which is lost through the previously mentioned "leaky" skin.

Steroid and retinoid products have been proven ineffective against Netherton syndrome, and may in fact make things worse for the affected individual.

Intravenous immunoglobulin has become established as the treatment of choice in Netherton's syndrome. This therapy reduces infection; enables improvement and even resolution of the skin and hair abnormalities, and dramatically improves quality of life of the patients; although exactly how it achieves this is not known. Given this; it is possible that the reason Netherton's usually is not very severe at or shortly after birth is due to a protective effect of maternal antibodies; which cross the placenta but wane by four to six months.

C2 deficiency has a prevalence of 1 in about 20,000 people in Western countries.

The cause of immunodeficiency varies depending on the nature of the disorder. The cause can be either genetic or acquired by malnutrition and poor sanitary conditions. Only for some genetic causes, the exact genes are known. Although there is no true discrimination to who this disease affects, the genes are passed from mother to child, and on occasion from father to child. Women tend not to show symptoms due to their second X chromosome not having the mutation while man are symptomatic, due to having one X chromosome.

The most commonly quoted figure for the prevalence of SCID is around 1 in 100,000 births, although this is regarded by some to be an underestimate of the true prevalence; some estimates predict that the prevalence rate is as high as 1 in 50,000 live births. A figure of about 1 in 65,000 live births has been reported for Australia.

Due to the genetic nature of SCID, a higher prevalence is found in areas and cultures among which there is a higher rate of consanguineous mating. A study conducted upon Moroccan SCID patients reported that inbreeding parenting was observed in 75% of the families.

Recent studies indicate that one in every 2,500 children in the Navajo population inherit severe combined immunodeficiency. This condition is a significant cause of illness and death among Navajo children. Ongoing research reveals a similar genetic pattern among the related Apache people.

WHIM Syndrome (or Warts, Hypogammaglobulinemia, Immunodeficiency, and Myelokathexis syndrome) is a rare congenital immunodeficiency disorder characterized by chronic noncyclic neutropenia.

Infusions of immune globulin can reduce the frequency of bacterial infections, and G-CSF or GM-CSF therapy improves blood neutrophil counts.

As WHIM syndrome is a molecular disease arising from gain-of-function mutations in CXCR4, preclinical studies identified plerixafor, a specific CXCR4 antagonist, as a potential mechanism-based therapeutic for the disease. Two subsequent clinical trials involving a handful of patients with WHIM syndrome demonstrated that plerixafor could increase white blood cell counts and continues to be a promising targeted therapy.

A woman with spontaneous remission of her WHIM syndrome due to Chromothripsis in one of her blood stem cells has been identified.

In support of these studies, a 2014 phase I clinical trial treated 3 patients diagnosed with WHIM syndrome with plerixafor twice a day for 6 months. All three patients presented with multiple reoccurring infections before treatment and all had an increase in their white blood cell count post treatment. One patient (P3) had a decrease in his infections by 40% while the remaining 2 patients (P1 and P2) had no infections throughout the entirety of the treatment. Plerixafor may also proof to have anti-human papillomavirus (HPV) properties as all patients experienced a shrinkage or complete disappearance of their warts. While this treatment shows promise in treating neutropenia (decreased white blood cells), this trial showed no increase of immune globulins in the body. A phase III clinical trial has been approved to compare the infection prevention ability of plerixafor versus the current treatment of G-CSF in patients with WHIM.

A review from 2000 stated that life expectancy was reduced because of a tendency to develop cancer relatively early as well as deaths due to infections related to immunodeficiency.

Netherton syndrome is a severe, autosomal recessive form of ichthyosis associated with mutations in the "SPINK5" gene. It is named after Earl W. Netherton (1910–1985), an American dermatologist who discovered it in 1958.

Serology (detection on antibodies to a specific pathogen or antigen) is often used to diagnose viral diseases. Because XLA patients lack antibodies, these tests always give a negative result regardless of their real condition. This applies to standard HIV tests. Special blood tests (such as the western blot based test) are required for proper viral diagnosis in XLA patients.

It is not recommended and dangerous for XLA patients to receive live attenuated vaccines such as live polio, or the measles, mumps, rubella (MMR vaccine). Special emphasis is given to avoiding the oral live attenuated SABIN-type polio vaccine that has been reported to cause polio to XLA patients. Furthermore, it is not known if active vaccines in general have any beneficial effect on XLA patients as they lack normal ability to maintain immune memory.

XLA patients are specifically susceptible to viruses of the Enterovirus family, and mostly to: polio virus, coxsackie virus (hand, foot, and mouth disease) and Echoviruses. These may cause severe central nervous system conditions as chronic encephalitis, meningitis and death. An experimental anti-viral agent, pleconaril, is active against picornaviruses. XLA patients, however, are apparently immune to the Epstein-Barr virus (EBV), as they lack mature B cells (and so HLA co-receptors) needed for the viral infection. Patients with XLA are also more likely to have a history of septic arthritis.

It is not known if XLA patients are able to generate an allergic reaction, as they lack functional IgE antibodies.There is no special hazard for XLA patients in dealing with pets or outdoor activities. Unlike in other primary immunodeficiencies XLA patients are at no greater risk for developing autoimmune illnesses.

Agammaglobulinemia (XLA) is similar to the primary immunodeficiency disorder Hypogammaglobulinemia (CVID), and their clinical conditions and treatment are almost identical. However, while XLA is a congenital disorder, with known genetic causes, CVID may occur in adulthood and its causes are not yet understood.

XLA was also historically mistaken as Severe Combined Immunodeficiency (SCID), a much more severe immune deficiency ("Bubble boys").A strain of laboratory mouse, XID, is used to study XLA. These mice have a mutated version of the mouse Btk gene, and exhibit a similar, yet milder, immune deficiency as in XLA.

Autoimmune polyendocrine syndrome type 1 is a condition caused in an autosomal recessive manner. Furthermore, it is due to a defect in AIRE gene (which helps to make a protein that is called the autoimmune regulator) mapped to 21q22.3 chromosome location, hence chromosome 21.

SCID mice were and still are used in disease, vaccine, and transplant research; especially as animal models for testing the safety of new vaccines or therapeutic agents in people with weakened immune system recessive gene with clinical signs similar to the human condition, also affects the Arabian horse. In horses, the condition remains a fatal disease, as the animal inevitably succumbs to an opportunistic infection within the first four to six months of life. However, carriers, who themselves are not affected by the disease, can be detected with a DNA test. Thus careful breeding practices can avoid the risk of an affected foal being produced.

Another animal with well-characterized SCID pathology is the dog. There are two known forms, an X-linked SCID in Basset Hounds that has similar ontology to X-SCID in humans, and an autosomal recessive form seen in one line of Jack Russell Terriers that is similar to SCID in Arabian horses and mice.

SCID mice also serve as a useful animal model in the study of the human immune system and its interactions with disease, infections, and cancer.