Infant mortality is high for patients diagnosed with early onset; mortality can occur within less than 2 months, while children diagnosed with late-onset syndrome seem to have higher rates of survival. Patients suffering from a complete lesion of mut0 have not only the poorest outcome of those suffering from methylaonyl-CoA mutase deficiency, but also of all individuals suffering from any form of methylmalonic acidemia.

No sexual predilection is observed because the deficiency of glycogen synthetase activity is inherited as an autosomal recessive trait.

The major morbidity is a risk of fasting hypoglycemia, which can vary in severity and frequency. Major long-term concerns include growth delay, osteopenia, and neurologic damage resulting in developmental delay, intellectual deficits, and personality changes.

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).

Genetic models of SLOS are created by knocking out the "DHCR7" gene. One study used homologous recombination to disrupt "DCHR7" in mouse embryonic stem cells. Similar to what is found in humans, heterozygous mice (having only one mutated allele) were phentoypically normal, and were crossed to produce pups (young mice) homozygous for the mutated allele. Although these pups died within the first day of life due to their inability to feed, they showed characteristics similar to humans with SLOS. They had decreased levels of cholesterol, increased levels of 7- and 8DHC, showed less growth and smaller birth weights, had craniofacial malformations, and less movement. Many also had a cleft palate, and decreased neuronal responses to glutamate. Overall however, the pups had fewer dysmorphic features than human patients with SLOS; they did not present limb, renal, adrenal or central nervous system malformations. This is explained by the fact that in rodents, maternal cholesterol can cross the placenta, and actually appears to be essential for the development of the fetus. In humans, very little maternal cholesterol is transferred to the fetus. In sum, the genetic mouse model is helpful to explain the neuropathophysiology of SLOS.

Glyceraldehyde 3-phosphate dehydrogenase (abbreviated as GAPDH or less commonly as G3PDH) () is an enzyme of ~37kDa that catalyzes the sixth step of glycolysis and thus serves to break down glucose for energy and carbon molecules. In addition to this long established metabolic function, GAPDH has recently been implicated in several non-metabolic processes, including transcription activation, initiation of apoptosis, ER to Golgi vesicle shuttling, and fast axonal, or axoplasmic transport. In sperm, a testis-specific isoenzyme GAPDHS is expressed.

Teratogenic models are induced by feeding pregnant rats or mice inhibitors of DCHR7. Two common inhibitors are BM15766 (4-(2-[1-(4-chlorocinnamyl)piperazin-4-yl]ethyl)-benzoic acid) and AY9944 (truns-l,4-bis(2-chlorobenzylaminomethy1)cyclohexane dihydrochloride). These compounds have different chemical and physical properties, but induce similar effects. AY9944 has been shown to induce holoprosencephaly and sexual malformations similar to those seen in humans with SLOS. It is also known to cause impairments in the serotonin receptor, another defect commonly seen in SLOS patients. BM15766 has produced the lack of cholesterol and bile acid synthesis that is seen in SLOS patients with homozygous mutations. All teratogenic models can be effectively used to study SLOS; however, they present lower levels of 7-DHC and 8-DHC than are seen in humans. This can be explained by the fact that humans experience a permanent block in their DHCR7 activity, where mice and rats treated with inhibitors experience only transient blocks. Furthermore, different species of mice and rats are more resistant to teratogens, and may be less effective as models of SLOS. Teratogenic models are most commonly used to study more long-term effects of SLOS, because they survive longer than genetic models. For example, one study examined the retinal degeneration of SLOS, which in rats does not occur until at least one month after birth.

Glycerol Kinase Deficiency (GKD) is an X-linked recessive enzyme defect that is heterozygous in nature. Three clinically distinct forms of this deficiency have been proposed, namely infantile, juvenile, and adult. National Institutes of Health and its Office of Rare Diseases Research (ORDR) branch classifies GKD as a rare disease, known to affect fewer than 200,000 individuals in the United States. The responsible gene lies in a region containing genes in which deletions can cause Duchenne muscular dystrophy and adrenal hypoplasia congenita. Combinations of these three genetic defects including GKD are addressed medically as Complex GKD.

Glycerol Kinase Deficiency has two main causes associated with it.

- The first cause is isolated enzyme deficiency. The enzyme glycerol kinase is encoded by the X-chromosome in humans. It acts as a catalyst in the phosphorylation of glycerol to glycerol-3-phosphate which plays a key role in formation of triacylglycerol (TAG) and fat storage. There is no genotype–phenotype correlation in isolated GKD and it can be either symptomatic or asymptomatic. Symptomatic means that GKD shows symptoms when it persists in the body and asymptomatic means that the no symptoms appear in the body. In this deficiency the genotype is not associated with the phenotype. The presence of certain mutations in genes has no relation with the phenotype i.e. any resulting physical traits or abnormality.

- The second cause is a deletion or mutation of a single gene. GKD is described by mendelian inheritance and is an X-linked recessive trait due to which it occurs mainly in males and occasionally in females. GKD results when the glycerol kinase gene present on the locus Xp21 of the X chromosome is either deleted or mutated. Females have two X chromosomes and males have one X and one Y chromosome .The expression of recessive genes on the X chromosome is different in males and females. This is due to the fact that genes present on the Y chromosome do not pair up with genes on the X chromosome in males. In females the disorder is expressed only when there are two copies of the affected gene present on each X chromosome but since the glycerol kinase gene is present only on one X chromosome the disorder is not expressed in women. Women have a second good copy that can compensate for the defect on the first copy. On the other hand, males only need a single copy of the recessive gene for the disorder to be expressed. They do not have a second copy that can protect against any defect on the first copy.

It is caused by the deficiency of the enzyme cystathionine beta synthase, and the deficiency of folic acid, vitamin B12 and pyridoxine (vitamin B6), or mutations of related enzymes.

Unlike other autoinflammatory disorders, patients with CANDLE do not respond to IL-1 inhibition treatment in order to stop the autoinflammatory response altogether. This suggests that the condition also involves IFN dysregulation.

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

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.

Janus kinase 3 deficiency or JAK3 deficiency is a defect in the body's cytokine receptors and their signaling. JAK3 encodes Janus kinase 3, a tyrosine kinase that belongs to the Janus family. JAK3 functions in signal transduction and interacts with members of the STAT (signal transduction and activators of transcription) family. The cause of JAK3 deficiency. The deficiency causes the near absence of T lymphocytes and Natural killer cells; and normal or elevated B lymphocytes due to an autosomal recessive variant of severe combined immunodeficiency (SCID).

The most common known cause of the syndrome are mutations in the Proteasome Subunit, Beta Type, 8 (PSMB8) gene that codes for proteasomes that in turn break down other proteins. This occurs specifically when a mutation causes the homozygous recessive form to emerge. The mutated gene results in proteins not being degraded and oxidative proteins building up in cellular tissues, eventually leading to apoptosis, especially in muscle and fat cells.

A study conducted by Brehm et al. in November 2015 discovered additional mutations that can cause CANDLE syndrome, including PSMA3 (encodes α7), PSMB4 (encodes β7), PSMB9 (encodes β1i), and the proteasome maturation protein (POMP), with 8 mutations in total between them. An additional unknown mutation type in the original PSMB8 gene was also noted.

Several tests can be done to discover the dysfunction of methylmalonyl-CoA mutase. Ammonia test, blood count, CT scan, MRI scan, electrolyte levels, genetic testing, methylmalonic acid blood test, and blood plasma amino acid tests all can be conducted to determine deficiency.

There is no treatment for complete lesion of the mut0 gene, though several treatments can help those with slight genetic dysfunction. Liver and kidney transplants, and a low-protein diet all help regulate the effects of the diseases.

The severity and prognosis vary with the type of mutation involved.

Bare lymphocyte syndrome is a condition caused by mutations in certain genes of the major histocompatibility complex or involved with the processing and presentation of MHC molecules. It is a form of severe combined immunodeficiency.

GAPDH is overexpressed in multiple human cancers, such as cutaneous melanoma, and its expression is positively correlated with tumor progression. Its glycolytic and antiapoptotic functions contribute to proliferation and protection of tumor cells, promoting tumorigenesis. Notably, GAPDH protects against telomere shortening induced by chemotherapeutic drugs that stimulate the sphingolipid ceramide. Meanwhile, conditions like oxidative stress impair GAPDH function, leading to cellular aging and death. Moreover, depletion of GAPDH has managed to induce senescence in tumor cells, thus presenting a novel therapeutic strategy for controlling tumor growth.

In dairy breeds, the disease may occur in calves between birth and 4 months of age. In rustic breeds or beef cattle, heifers and young steers up to 12 months of age can be affected. In calves, muscles in upper portion of the front legs and the hind legs are degraded, causing the animal to have a stiff gait and it may have difficulty standing. The disease may also present in the form of respiratory distress.

Xeroderma pigmentosum (XP) is a rare autosomal recessive genetic disorder of DNA repair in which the ability to repair damage caused by ultraviolet (UV) light is deficient. In extreme cases, "all" exposure to sunlight must be forbidden, no matter how small; as such, individuals with the disease are often colloquially referred to as "Moon children". Multiple basal cell carcinomas (basaliomas) and other skin malignancies frequently occur at a young age in those with XP; metastatic malignant melanoma and squamous cell carcinoma are the two most common causes of death in XP victims. This disease is present in both genders and in all races, with an incidence of 1:250,000 in the United States. XP is roughly six times more common in Japanese people than in other groups.

Normally, damage to DNA in epidermal cells occurs during exposure to UV light. The absorption of the high-energy light leads to the formation of pyrimidine dimers, namely cyclobutane-pyrimidine dimers and pyrimidine-6-4-pyrimidone photoproducts. In a healthy, normal human being, the damage is first excised by endonucleases. DNA polymerase then repairs the missing sequence, and ligase "seals" the transaction. This process is known as nucleotide excision repair.

Different genetic causes and types of Leigh syndrome have different prognoses, though all are poor. The most severe forms of the disease, caused by a full deficiency in one of the affected proteins, cause death at a few years of age. If the deficiency is not complete, the prognosis is somewhat better and an affected child is expected to survive 6–7 years, and in rare cases, to their teenage years.

A deficiency of vitamin B alone is relatively uncommon and often occurs in association with other vitamins of the B complex. The elderly and alcoholics have an increased risk of vitamin B deficiency, as well as other micronutrient deficiencies. Evidence exists for decreased levels of vitamin B in women with type 1 diabetes and in patients with systemic inflammation, liver disease, rheumatoid arthritis, and those infected with HIV. Use of oral contraceptives and treatment with certain anticonvulsants, isoniazid, cycloserine, penicillamine, and hydrocortisone negatively impact vitamin B status. Hemodialysis reduces vitamin B plasma levels.

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.

Type 1 tyrosinemia, also known as hepatorenal tyrosinemia or tyrosinosis, is the most severe form of tyrosinemia, a buildup of too much of the amino acid tyrosine in the blood and tissues due to an inability to metabolize it. It is caused by a deficiency of the enzyme fumarylacetoacetate hydrolase.