The cause of complement deficiency is genetics (though cases of an acquired nature do exist post infection). The majority of complement deficiencies are autosomal recessive, while properdin deficiency could be X-linked inheritance, and finally MBL deficiency can be both.

Acquired hypocomplementemia may occur in the setting of bone infections (osteomyelitis), infection of the lining of the heart (endocarditis), and cryoglobulinemia. Systemic lupus erythematosus is associated with low C3 and C4 Membranoproliferative glomerulonephritis usually has low C3.

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.

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.

Heterozygous protein C deficiency occurs in 0.14–0.50% of the general population. Based on an estimated carrier rate of 0.2%, a homozygous or compound heterozygous protein C deficiency incidence of 1 per 4 million births could be predicted, although far fewer living patients have been identified. This low prevalence of patients with severe genetic protein C deficiency may be explained by excessive fetal demise, early postnatal deaths before diagnosis, heterogeneity in the cause of low concentrations of protein C among healthy individuals and under-reporting.

The incidence of protein C deficiency in individuals who present with clinical symptoms has been reported to be estimated at 1 in 20,000.

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.

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.

Current research suggests that nearly 8% of the population has at least partial DPD deficiency. A diagnostics determination test for DPD deficiency is available and it is expected that with a potential 500,000 people in North America using 5-FU this form of testing will increase. The whole genetic events affecting the DPYD gene and possibly impacting on its function are far from being elucidated, and epigenetic regulations could probably play a major role in DPD deficiency. It seems that the actual incidence of DPD deficiency remains to be understood because it could depend on the very technique used to detect it. Screening for genetic polymorphisms affecting the "DPYD" gene usually identify less than 5% of patients bearing critical mutations, whereas functional studies suggest that up to 20% of patients could actually show various levels of DPD deficiency.

Women could be more at risk than men. It is more common among African-Americans than it is among Caucasians.

PNP-deficiency is extremely rare. Only 33 patients with the disorder in the United States have been documented. In the United Kingdom only one child has been diagnosed with this disorder.

Protein C deficiency is a rare genetic trait that predisposes to thrombotic disease. It was first described in 1981. The disease belongs to a group of genetic disorders known as thrombophilias. Protein C deficiency is associated with an increased incidence of venous thromboembolism (relative risk 8–10), whereas no association with arterial thrombotic disease has been found.

This condition is very rare; approximately 600 cases have been reported worldwide. In most parts of the world, only 1% to 2% of all infants with high phenylalanine levels have this disorder. In Taiwan, about 30% of newborns with elevated levels of phenylalanine have a deficiency of THB.

Vitamin E deficiency is rare and is almost never caused by a poor diet. Instead, there are three specific situations when a vitamin E deficiency is likely to occur:

- Premature, very low birth weight infants - birth weights less than 1500 grams, or 3.5 pounds. A neonatologist, a pediatrician specializing in the care of newborns, typically evaluates the nutritional needs of premature infants.

- Rare disorders of fat metabolism - There is a rare genetic condition termed isolated vitamin E deficiency or 'ataxia with isolated with vitamin E deficiency', caused by mutations in the gene for the tocopherol transfer protein. These individuals have an extremely poor capacity to absorb vitamin E and develop neurological complications that are reversed by high doses of vitamin E.

- Fat malabsorption - Some dietary fat is needed for the absorption of vitamin E from the gastrointestinal tract. Anyone diagnosed with cystic fibrosis, individuals who have had part or all of their stomach removed or who have had a gastric bypass, and individuals with malabsorptive problems such as Crohn's disease, liver disease or exocrine pancreatic insufficiency may not absorb fat (people who cannot absorb fat often pass greasy stools or have chronic diarrhea and bloating). Abetalipoproteinemia is a rare inherited disorder of fat metabolism that results in poor absorption of dietary fat and vitamin E. The vitamin E deficiency associated with this disease causes problems such as poor transmission of nerve impulses, muscle weakness, and degeneration of the retina that can cause blindness.

Inherited or congenital FX deficiency is passed on by autosomal recessive inheritance. A person needs to inherit a defective gene from both parents. People who have only one defective gene usually do not exhibit the disease, but can pass the gene on to half their offspring. Different genetic mutations have been described.

In persons with congenital FX deficiency the condition is lifelong. People affected should alert other family members as they may also have the condition or carry the gene. In the general population the condition affects about 1 in 1 million people. However, the prevalence may be higher as not all individuals may express the disease and be diagnosed.

In the acquired form of FX deficiency an insufficient amount of factor X is produced by the liver due to liver disease, vitamin K deficiency, buildup of abnormal proteins in organs (amyloidosis) or certain medications (i.e. warfarin). In amyloidosis FX deficiency develops as FX and other coagulation factors are absorbed by amyloid fibrils.

Some situations that increase the need for folate include the following:

- hemorrhage

- kidney dialysis

- liver disease

- malabsorption, including celiac disease and fructose malabsorption

- pregnancy and lactation (breastfeeding)

- tobacco smoking

- alcohol consumption

Cause of this deficiency is divided into "primary" and "secondary":

- Primary the International Union of Immunological Societies classifies primary immune deficiencies of the humoral system as follows:

- Secondary secondary (or acquired) forms of humoral immune deficiency are mainly due to hematopoietic malignancies and infections that disrupt the immune system:

Inherited or congenital FX deficiency is usually passed on by autosomal recessive inheritance. A person needs to inherit a defective gene from both parents. People who have only one defective gene are asymptomatic, but may have lower FXII levels and can pass the gene on to half their offspring.

In persons with congenital FXII deficiency the condition is lifelong. People affected may want to alert other family members as they may also may carry the gene. A 1994 study of 300 healthy blood donors found that 7 persons (2.3%) had FXII deficiencies with one subject having no detectable FXII (0.3%). This study is at variance with estimates that only 1 in 1,000,000 people has the condition.

The acquired form of FXII deficiency is seen in patients with the nephrotic syndrome, liver disease, sepsis and shock, disseminated intravascular coagulation, and other diseases.

Factor X deficiency (X as Roman numeral ten) is a bleeding disorder characterized by a lack in the production of factor X (FX), an enzyme protein that causes blood to clot in the coagulation cascade. Produced in the liver FX when activated cleaves prothrombin to generate thrombin in the intrinsic pathway of coagulation. This process is vitamin K dependent and enhanced by activated factor V.

The condition may be inherited or, more commonly, acquired.

While it is indicated that people with FXII deficiency are generally asymptomatic, studies in women with recurrent miscarriages suggest an association with FXII deficiency.

The condition is of importance in the differential diagnosis to other bleeding disorders, specifically the hemophilias: hemophilia A with a deficiency in factor VIII or antihemophilic globulin, hemophilia B with a deficiency in factor IX (Christmas disease), and hemophilia C with a deficiency in factor XI. Other rare forms of bleeding disorders are also in the differential diagnosis.

There is concern that individuals with FXII deficiency are more prone to thrombophilic disease, however, this is at variance with a long term study from Switzerland.

Based on the results of worldwide screening of biotinidase deficiency in 1991, the incidence of the disorder is:

5 in 137,401 for profound biotinidase deficiency

- One in 109,921 for partial biotinidase deficiency

- One in 61,067 for the combined incidence of profound and partial biotinidase deficiency

- Carrier frequency in the general population is approximately one in 120.

Treatment for "B cell deficiency"(humoral immune deficiency) depends on the cause, however generally the following applies:

- Treatment of infection(antibiotics)

- Surveillance for malignancies

- Immunoglobulin replacement therapy

Folate is found in leafy green vegetables. Multi-vitamins also tend to include Folate as well as many other B vitamins. B vitamins, such as Folate, are water-soluble and excess is excreted in the urine.

When cooking, use of steaming, a food steamer, or a microwave oven can help keep more folate content in the cooked foods, thus helping to prevent folate deficiency.

Folate deficiency during human pregnancy has been associated with an increased risk of infant neural tube defects. Such deficiency during the first four weeks of gestation can result in structural and developmental problems. NIH guidelines recommend oral B vitamin supplements to decrease these risks near the time of conception and during the first month of pregnancy.

The life expectancy of patients with homocystinuria is reduced only if untreated. It is known that before the age of 30, almost one quarter of patients die as a result of thrombotic complications (e.g., heart attack).

Protein S deficiency is a disorder associated with increased risk of venous thrombosis. Protein S, a vitamin K-dependent physiological anticoagulant, acts as a nonenzymatic cofactor to activate protein C in the degradation of factor Va and factor VIIIa. Decreased (antigen) levels or impaired function of protein S leads to decreased degradation of factor Va and factor VIIIa and an increased propensity to venous thrombosis. Protein S circulates in human plasma in two forms: approximately 60 percent is bound to complement component C4b β-chain while the remaining 40 percent is free, only free protein S has activated protein C cofactor activity

A 1999 retrospective study of 74 cases of neonatal onset found that 32 (43%) patients died during their first hyperammonemic episode. Of those who survived, less than 20% survived to age 14. Few of these patients received liver transplants.

IgG deficiency (Selective deficiency of immunoglobulin G) is a form of dysgammaglobulinemia where the proportional levels of the IgG isotype are reduced relative to other immunoglobulin isotypes. IgG deficiency is often found in children as transient hypogammaglobulinemia of infancy (THI), which may occur with or without additional decreases in IgA or IgM.

IgG has four subclasses: IgG, IgG, IgG, and IgG. It is possible to have either a global IgG deficiency, or a deficiency of one or more specific subclasses of IgG. The main clinically relevant form of IgG deficiency is IgG. IgG deficiency is not usually encountered without other concomitant immunoglobulin deficiencies, and IgG deficiency is very common but usually asymptomatic.

IgG1 is present in the bloodstream at a percentage of about 60-70%, IgG2-20-30%, IgG3 about 5-8 %, and IgG4 1-3 %. IgG subclass deficiencies affect only IgG subclasses (usually IgG2 or IgG3), with normal total IgG and IgM immunoglobulins and other components of the immune system being at normal levels. These deficiencies can affect only one subclass or involve an association of two subclasses, such as IgG2 and IgG4. IgG deficiencies are usually not diagnosed until the age of 10. Some of the IgG levels in the blood are undetectable and have a low percentage such as IgG4, which makes it hard to dertermine if a deficiency is actually present. IgG subclass deficiencies are sometimes correlated with bad responses to pneumoccal polyscaccharides, especially IgG2 and or IgG4 deficiency. Some of these deficiencies are also involved with pancreatitis and have been linked to IgG4 levels.