A 2014 review stated that 25% and 30% of identified suffers die in the first two decades of life, mainly due to lack of treatment.

Because hereditary angioedema is an autosomal inheritable disease, there is no gender difference in transmission and both sexes are equally likely to receive the mutated gene from their parent(s). The figure below "(courtesy of US National Library Of Medicine)" depicts autosomal dominant transmission. Here, the father (individual A) with a mutated gene for HAE, has the disease while his wife (individual B) with 2 non-mutated copies of the C1 inhibitor gene and does not have the disease. The possibility of a cross between them gives the possibilities as shown: two of their offspring will have the disease (HEA) while the others would not.

The affected father who has HAE has a mutation on one of his genes (C1-INH). Each one of his children, notwithstanding his/her sex, will have a 50% chance to inherit the mutated C1-INH gene from him. HAE is generally referred to as a "dominant" condition because it only takes a mutation in one of the two C1-INH genes in a carrier to cause the disease.

The prevalence of HAE is relatively low – between 1 in every 10,000 to 1 in every 50,000 persons. Most persons with HAE acquire a C1 esterase inhibitor (C1-INH) mutation from one of their parents. A parent with HAE usually has a 50% probability of transmitting this condition on to one of his/her children of either sex as shown in the figure (HEA Inheritance).

In occasions when HAE is not inherited and occurs in people with no previous history of it. This is because there are new impulsive or spontaneous changes in the sperm or egg cell that is responsible for this specific pregnancy. In a review of patients who do not have a history of HAE in their family, but who have relatively low levels of mutated C1-INH with persistent angioedema, 25% of new patients who had HAE had C1-INH changes that do not show signs of being inherited but rather new.

The mutational changes in 1 or both of the carriers' C1 inhibitor genes could have only occurred spontaneously, and just like in the example above, their offspring in this case will have a 50% probability of acquiring the mutated gene from either parent that has HAE.

Hereditary angioedema (HAE) exists in three forms, all of which are caused by a genetic mutation inherited in an autosomal dominant form. They are distinguished by the underlying genetic abnormality. Types I and II are caused by mutations in the "SERPING1" gene, which result in either diminished levels of the C1-inhibitor protein (type I HAE) or dysfunctional forms of the same protein (type II HAE). Type III HAE has been linked with mutations in the "F12" gene, which encodes the coagulation protein factor XII. All forms of HAE lead to abnormal activation of the complement system, and all forms can cause swelling elsewhere in the body, such as the digestive tract. If HAE involves the larynx, it can cause life-threatening asphyxiation. The pathogenesis of this disorder is suspected to be related to unopposed activation of the contact pathway by the initial generation of kallikrein and/or clotting factor XII by damaged endothelial cells. The end product of this cascade, bradykinin, is produced in large amounts and is believed to be the predominant mediator leading to increased vascular permeability and vasodilation that induces typical angioedema "attacks".

Angioedema is an area of swelling of the lower layer of skin and tissue just under the skin or mucous membranes. The swelling may occur in the face, tongue, larynx, abdomen, or arms and legs. Often it is associated with hives, which are swelling within the upper skin. Onset is typically over minutes to hours.

The underlying mechanism typically involves histamine or bradykinin. The version related to histamine is to due an allergic reaction to agents such as insect bites, foods, or medications. The version related to bradykinin may occur due to an inherited problem known as C1 esterase inhibitor deficiency, medications known as angiotensin converting enzyme inhibitors, or a lymphoproliferative disorder.

Efforts to protect the airway may include intubation or cricothyroidotomy. Histamine related angioedema can be treated with antihistamines, corticosteroids, and epinephrine. In those with bradykinin related disease a C1 esterase inhibitor, ecallantide, or icatibant may be used. Fresh frozen plasma may be used instead. In the United States the disease affects about 100,000 people a year.

HSAN I constitutes a clinically and genetically heterogeneous group of diseases of low prevalence. Detailed epidemiological data are currently not available. The frequency of the disease is still reflected by reports of a handful affected families. Although the impressive clinical features of HSAN I are seen by neurologists, general practitioners, orthopedists, and dermatologists, the condition might still be under-recognized particularly for sporadic cases and patients who do not exhibit the characteristic clinical features.

The epidemiology of rapidly progressive glomerulonephritis according to Hedger, et al., is an incidence rate of 3.9 individuals per million (3.3–4.7) with a 95% confidence intervals.

Membranoproliferative glomerulonephritis ("MPGN"), also known as mesangiocapillary glomerulonephritis, is a type of glomerulonephritis caused by deposits in the kidney glomerular mesangium and basement membrane (GBM) thickening, activating complement and damaging the glomeruli.

MPGN accounts for approximately 4% of primary renal causes of nephrotic syndrome in children and 7% in adults.

It should not be confused with membranous glomerulonephritis, a condition in which the basement membrane is thickened, but the mesangium is not.

Genetic counseling is an important tool for preventing new cases if this is wished by at-risk family members. Appropriate genetic counseling is based on an accurate diagnosis. Therefore, clinicians and genetic counselors should use ulcero-mutilating complications as the main diagnostic criteria. Since the disease is inherited as an autosomal dominant trait, there is a Mendelian risk of 50% for subsequent generations regardless of their sex. Prenatal testing for pregnancies at increased risk is possible if the disease-causing mutation has been identified in the family. Predictive testing is useful for young people to avoid serious complications of the disease.

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.

A large British study from 2008 found a median estimated life expectancy of 11.6 years.

The bare lymphocyte syndrome, type II (BLS II) is a rare recessive genetic condition in which a group of genes called major histocompatibility complex class II (MHC class II) are not expressed.

The result is that the immune system is severely compromised and cannot effectively fight infection. Clinically, this is similar to severe combined immunodeficiency (SCID), in which lymphocyte precursor cells are improperly formed. As a notable contrast, however, bare lymphocyte syndrome does not result in decreased B- and T-cell counts, as the development of these cells is not impaired.

Diarrhea can be among the associated conditions.

Autosomal dominant porencephaly type I is rare and its prevalence and incidence are unknown. It affects males and females equally.

Membranoproliferative glomerulonephritis involves deposits at the intraglomerular mesangium.

It is also the main hepatitis C associated nephropathy.

It also is related to a number of autoimmune diseases, prominently systemic lupus erythematosus (SLE). Also found with Sjögren syndrome, rheumatoid arthritis, inherited complement deficiencies (esp C2 deficiency), scleroderma, Celiac disease.

The histomorphologic differential diagnosis includes transplant glomerulopathy and thrombotic microangiopathies.

Rapidly progressive glomerulonephritis (RPGN) is a syndrome of the kidney that is characterized by a rapid loss of renal function, (usually a 50% decline in the glomerular filtration rate (GFR) within 3 months) with glomerular crescent formation seen in at least 50% or 75% of glomeruli seen on kidney biopsies. If left untreated, it rapidly progresses into acute renal failure and death within months. In 50% of cases, RPGN is associated with an underlying disease such as Goodpasture syndrome, systemic lupus erythematosus or granulomatosis with polyangiitis; the remaining cases are idiopathic. Regardless of the underlying cause, RPGN involves severe injury to the kidneys' glomeruli, with many of the glomeruli containing characteristic glomerular crescents (crescent-shaped scars).

Type I hypersensitivity (or immediate hypersensitivity) is an allergic reaction provoked by reexposure to a specific type of antigen referred to as an allergen. Type I is not to be confused with type II, type III, or type IV hypersensitivities, nor is it to be confused with Type I Diabetes or Type I of any other disease or reaction.

Exposure may be by ingestion, inhalation, injection, or direct contact.

Some examples:

- Allergic asthma

- Allergic conjunctivitis

- Allergic rhinitis ("hay fever")

- Anaphylaxis

- Angioedema

- Urticaria (hives)

- Eosinophilia

- Penicillin allergy

- Cephalosporin allergy

- Food allergy

- Sweet itch

Hurler syndrome has an overall frequency of one per 100,000. The mucopolysaccharidoses as a whole have a frequency of one in every 25,000 births.

Treatment for autosomal dominant porencephaly type I is based on the symptoms that an individual is experiencing - for example, treatment of seizures with anticonvulsants. It is particularly important for individuals with this disorder and hypertension to control their blood pressure, as they are at higher risk of stroke. Other stroke prevention treatments include avoiding anticoagulants, smoking, and situations that may lead to head trauma.

Opitz G/BBB Syndrome is a rare genetic condition caused by one of two major types of mutations: MID1 mutation on the short (p) arm of the X chromosome or a mutation of the 22q11.2 gene on the 22nd chromosome. Since it is a genetic disease, it is an inherited condition. However, there is an extremely wide variability in how the disease presents itself.

In terms of prevention, several researchers strongly suggest prenatal testing for at-risk pregnancies if a MID1 mutation has been identified in a family member. Doctors can perform a fetal sex test through chromosome analysis and then screen the DNA for any mutations causing the disease. Knowing that a child may be born with Opitz G/BBB syndrome could help physicians prepare for the child’s needs and the family prepare emotionally. Furthermore, genetic counseling for young adults that are affected, are carriers or are at risk of carrying is strongly suggested, as well (Meroni, Opitz G/BBB syndrome, 2012). Current research suggests that the cause is genetic and no known environmental risk factors have been documented. The only education for prevention suggested is genetic testing for at-risk young adults when a mutation is found or suspected in a family member.

One 10-year-old girl with Crigler–Najjar syndrome type I was successfully treated by liver cell transplantation.

The homozygous Gunn rat, which lacks the enzyme uridine diphosphate glucuronyltransferase (UDPGT), is an animal model for the study of Crigler–Najjar syndrome. Since only one enzyme is working improperly, gene therapy for Crigler-Najjar is a theoretical option which is being investigated.

A 2005 study on rats suggested that hyperprolininemia causes cognitive dysfunction.

Inclusion-cell (I-cell) disease, also referred to as mucolipidosis II (ML II), is part of the lysosomal storage disease family and results from a defective phosphotransferase (an enzyme of the Golgi apparatus). This enzyme transfers phosphate to mannose residues on specific proteins. Mannose 6 phosphate serves as a marker for them to be targeted to lysosomes within the cell. Without this marker, the proteins are instead excreted outside the cell—the default pathway for proteins moving through the Golgi apparatus. Lysosomes cannot function without these proteins, which function as catabolic enzymes for the normal breakdown of substances (e.g. oligosaccharides, lipids, and glycosaminoglycans) in various tissues throughout the body (i.e. fibroblasts). As a result, a buildup of these substances occurs within lysosomes because they cannot be degraded, resulting in the characteristic I-cells, or "inclusion cells". These cells can be identified under the microscope. In addition, the defective lysosomal enzymes normally found only within lysosomes are instead found in high concentrations in the blood.

Mucolipidosis type I (ML I) or sialidosis is an inherited lysosomal storage disease that results from a deficiency of the enzyme alpha-N -acetyl neuraminidase (sialidase). The lack of this enzyme results in an abnormal accumulation of complex carbohydrates known as mucopolysaccharides, and of fatty substances known as mucolipids. Both of these substances accumulate in bodily tissues.

A congenital disorder of glycosylation (previously called carbohydrate-deficient glycoprotein syndrome) is one of several rare inborn errors of metabolism in which glycosylation of a variety of tissue proteins and/or lipids is deficient or defective. Congenital disorders of glycosylation are sometimes known as CDG syndromes. They often cause serious, sometimes fatal, malfunction of several different organ systems (especially the nervous system, muscles, and intestines) in affected infants. The most common subtype is CDG-Ia (also referred to as PMM2-CDG) where the genetic defect leads to the loss of phosphomannomutase 2, the enzyme responsible for the conversion of mannose-6-phosphate into mannose-1-phosphate.

Hyperprolinemia type II results in proline levels in the blood between 10 and 15 times higher than normal, and high levels of a related compound called pyrroline-5-carboxylate. This rare form of the disorder may appear benign at times, but often involves seizures, convulsions, and intellectual disability.

Hyperprolinemia can also occur with other conditions, such as malnutrition or liver disease. In particular, individuals with conditions that cause elevated levels of lactic acid in the blood, such as lactic acidemia, are likely to have elevated proline levels, because lactic acid inhibits the breakdown of proline.