Ethylmalonic encephalopathy (EE) is a rare autosomal recessive inborn error of metabolism. Patients affected with EE are typically identified shortly after birth, with symptoms including diarrhea, petechiae and seizures. The genetic defect in EE is thought to involve an impairment in the degradation of sulfide intermediates in the body. Hydrogen sulfide then builds up to toxic levels. EE was initially described in 1994. Most cases of EE have been described in individuals of Mediterranean or Arabic origin.

Mutations in the "ETHE1" gene cause ethylmalonic encephalopathy. The "ETHE1" gene makes an enzyme that plays an important role in energy production. It is active in mitochondria, which are the energy-producing centers within cells. Little is known about its exact function, however.

Mutations in the "ETHE1" gene lead to the production of a defective version of the enzyme or prevents the enzyme from being made. A lack of the ETHE1 enzyme impairs the ability to make energy in mitochondria. Additionally, a loss of this enzyme allows potentially toxic compounds, including ethylmalonic acid and lactic acid, to build up in the body. Excess amounts of these compounds can be detected in urine. It remains unclear how a loss of the ETHE1 enzyme leads to progressive brain dysfunction and the other features of ethylmalonic encephalopathy.

Ethylmalonic encephalopathy is an autosomal recessive disorder, which means the defective gene is located on an autosome, and both parents must carry one copy of the defective gene in order to have a child born with the disorder. The parents of a child with an autosomal recessive disorder are usually not affected by the disorder.

Environmental enteropathy is believed to result in chronic malnutrition and subsequent growth stunting (low height-for-age measurement) as well as other child development deficits.

EE is rarely symptomatic and is considered a subclinical condition. However, adults may have mild symptoms or malabsorption such as altered stool consistency, increased stool frequency and weight loss.

GERD may lead to Barrett's esophagus, a type of intestinal metaplasia, which is in turn a precursor condition for esophageal cancer. The risk of progression from Barrett's to dysplasia is uncertain, but is estimated at about 20% of cases. Due to the risk of chronic heartburn progressing to Barrett's, EGD every five years is recommended for people with chronic heartburn, or who take drugs for chronic GERD.

GERD is caused by a failure of the lower esophageal sphincter. In healthy patients, the "Angle of His"—the angle at which the esophagus enters the stomach—creates a valve that prevents duodenal bile, enzymes, and stomach acid from traveling back into the esophagus where they can cause burning and inflammation of sensitive esophageal tissue.

Factors that can contribute to GERD:

- Hiatal hernia, which increases the likelihood of GERD due to mechanical and motility factors.

- Obesity: increasing body mass index is associated with more severe GERD. In a large series of 2,000 patients with symptomatic reflux disease, it has been shown that 13% of changes in esophageal acid exposure is attributable to changes in body mass index.

- Zollinger-Ellison syndrome, which can be present with increased gastric acidity due to gastrin production.

- A high blood calcium level, which can increase gastrin production, leading to increased acidity.

- Scleroderma and systemic sclerosis, which can feature esophageal dysmotility.

- The use of medicines such as prednisolone.

- Visceroptosis or Glénard syndrome, in which the stomach has sunk in the abdomen upsetting the motility and acid secretion of the stomach.

GERD has been linked to a variety of respiratory and laryngeal complaints such as laryngitis, chronic cough, pulmonary fibrosis, earache, and asthma, even when not clinically apparent. These atypical manifestations of GERD are commonly referred to as laryngopharyngeal reflux (LPR) or as extraesophageal reflux disease (EERD).

Factors that have been linked with GERD, but not conclusively:

- Obstructive sleep apnea

- Gallstones, which can impede the flow of bile into the duodenum, which can affect the ability to neutralize gastric acid

In 1999, a review of existing studies found that, on average, 40% of GERD patients also had "H. pylori" infection. The eradication of "H. pylori" can lead to an increase in acid secretion, leading to the question of whether "H. pylori"-infected GERD patients are any different than non-infected GERD patients. A double-blind study, reported in 2004, found no clinically significant difference between these two types of patients with regard to the subjective or objective measures of disease severity.

EoE is a relatively poorly understood disease of which awareness is rising.

At a tissue level, EoE is characterized by a dense infiltrate with white blood cells of the eosinophil type into the epithelial lining of the esophagus. This is thought to be an allergic reaction against ingested food, based on the important role eosinophils play in allergic reactions. Eosinophils are inflammatory cells that release a variety of chemical signals which inflame the surrounding esophageal tissue. This results in the signs and symptoms of pain, visible redness on endoscopy, and a natural history that may include stricturing.

Treatment strategies may include medication, dietary modification to exclude food allergens, and mechanical dilatation of the esophagus.

The current recommendation for first line treatment is PPI in lieu of diet as more than half of people with EOE respond to this, and it is a low risk, low cost treatment. The next step treatment is topical corticosteroids (topical viscous budesonide or fluticasone).

Dietary treatment can be effective, as there does appear to be a role of allergy in the development of EOE. Allergy testing is not particularly effective in predicting which foods are driving the disease process. Various approaches have been tried, where either six food groups (cow´s milk, wheat, egg, soy, nuts and fish/seafood), four groups (animal milk, gluten-containing cereals, egg, legumes) or two groups (animal milk and gluten-containing cereals) are excluded for a period of time, usually six weeks. Endoscopy is required to measure the response to the dietary measure. A "top down" (starting with six foods, then reintroducing) approach may be very restrictive. Four- or even two-group exclusion diets may be less difficult to follow and reduce the need for many endoscopies if the response to the limited restriction is good.

Endoscopic dilatation is sometimes required if there is significant narrowing of the esophagus. This is effective in 84% of people who require this procedure.

There have been hypotheses about visual looming syndrome to be linked with several neural and gastroenterology diseases, such as celiac disease, epilepsy and migraines. Also physical differences between the eyes, such as astigmatism may be a factor. There have not been any empirical medical studies about the syndrome, though the consensus is all these may have affect on the muscular function of the eye, but most likely the visual looming syndrome is a separate symptom. There have been studies of a similar neurological situation. Gabbiani Peron has studied the "looming stimulus selectivity in a collision-detecting neuron". Beverley Regan has studied "Binocular and monocular stimuli for motion in depth". Moors P, Huygelier H, Wagemans J, de-Wit L, van Ee R; "Suppressed visual looming stimuli are not integrated with auditory looming signals"

Peer to peer studies have shown many common symptoms, such are "fear of pointy objects hitting the eye", "weird sensation behind the eyes", "difficulty in focusing on objects nearby, which are moving and are not operated by the observer, such as windscreen wipers or a pencil someone else is holding". In these studies visual looming syndrome is often referred as sharp edges eye syndrome (SEES).

Visual looming syndrome is a problem with visual perception that causes people to inaccurately think that a stationary object is moving towards them, and might poke their eyes.

It is a neurological and muscular state, where faulty eye coordination causes the brain to interpret incoming information as a visual looming event (i.e. feeling that an object is approaching and might hit the eye). Because this condition is muscular in nature, anything that causes eye cooperation to fail, such as being tired, under the of narcotics or alcohol, or even minor differences in eye pressure or eyesight (e.g. nearsightedness), may be the cause of an episode. The is usually a narrow or pointy object which is near enough to cause confusion in the eyes, or which is in front of an undetermined or busy background. Some peer to peer studies have indicated that certain conditions, such as nyctalopia or night blindness, may worsen the syndrome.

The disease can remit spontaneously or become chronic, with exacerbations and remissions. In some persons, it can progress to pulmonary fibrosis and death. About half of cases resolve without treatment or can be cured within 12–36 months, and most within five years. Some cases, however, may persist several decades. Two-thirds of people with the condition achieve a remission within 10 years of the diagnosis. When the heart is involved, the prognosis is generally less favourable, though corticosteroids appear effective in improving AV conduction. The prognosis tends to be less favourable in African Americans than in white Americans.

Some 1990s studies indicated that persons with sarcoidosis appear to be at significantly increased risk for cancer, in particular lung cancer, lymphomas, and cancer in other organs known to be affected in sarcoidosis. In sarcoidosis-lymphoma syndrome, sarcoidosis is followed by the development of a lymphoproliferative disorder such as non-Hodgkin lymphoma. This may be attributed to the underlying immunological abnormalities that occur during the sarcoidosis disease process. Sarcoidosis can also follow cancer or occur concurrently with cancer. There have been reports of hairy cell leukemia, acute myeloid leukemia, and acute myeloblastic leukemia associated with sarcoidosis.

Sometimes, sarcoidosis, even untreated, can be complicated by opportunistic infections.

The heritability of sarcoidosis varies according to ethnicity. About 20% of African Americans with sarcoidosis have a family member with the condition, whereas the same figure for European Americans is about 5%. Additionally, in African Americans, who seem to experience more severe and chronic disease, siblings and parents of sarcoidosis cases have about a 2.5-fold increased risk for developing the disease. Investigations of genetic susceptibility yielded many candidate genes, but only few were confirmed by further investigations and no reliable genetic markers are known. Currently, the most interesting candidate gene is "BTNL2"; several "HLA-DR" risk alleles are also being investigated. In persistent sarcoidosis, the HLA haplotype "HLA-B7-DR15" are either cooperating in disease or another gene between these two loci is associated. In nonpersistent disease, there is a strong genetic association with HLA DR3-DQ2. Cardiac sarcoid has been connected to TNFA variants.

The cause of POF is usually idiopathic. Some cases of POF are attributed to autoimmune disorders, others to genetic disorders such as Turner syndrome and Fragile X syndrome. An Indian study showed a strong correlation between incidence of POF and certain variants in the inhibin alpha gene. In many cases, the cause cannot be determined. Chemotherapy and radiation treatments for cancer can sometimes cause ovarian failure. In natural menopause, the ovaries usually continue to produce low levels of hormones, but in chemotherapy or radiation-induced POF, the ovaries will often cease all functioning and hormone levels will be similar to those of a woman whose ovaries have been removed. Women who have had a hysterectomy tend to go through menopause several years earlier than average, likely due to decreased blood flow to the ovaries. Family history and ovarian or other pelvic surgery earlier in life are also implicated as risk factors for POF.

There are two basic kinds of premature ovarian failure. Case 1) where there are few to no remaining follicles and case 2) where there are an abundant number of follicles. In the first situation the causes include genetic disorders, autoimmune damage, chemotherapy, radiation to the pelvic region, surgery, endometriosis and infection. In most cases the cause is unknown. In the second case one frequent cause is autoimmune ovarian disease which damages maturing follicles, but leaves the primordial follicles intact. Also, in some women FSH may bind to the FSH receptor site, but be inactive. By lowering the endogenous FSH levels with ethinylestradiol (EE) or with a GnRH-a the receptor sites are free and treatment with exogenous recombinant FSH activates the receptors and normal follicle growth and ovulation can occur. (Since the serum anti-müllerin hormone (AMH) level is correlated with the number of remaining primordial follicles some researchers believe the above two phenotypes can be distinguished by measuring serum AMH levels.)

- Genetic disorders

- Autoimmune diseases

- Tuberculosis of the genital tract

- Smoking

- Radiation and/or chemotherapy

- Ovarian failure following hysterectomy

- Prolonged GnRH (Gonadatrophin Releasing Hormone) therapy

- Enzyme defects

- Resistant ovary

- Induction of multiple ovulation in infertility

Genetic associations include:

It has been estimated that POF affects 1% of the female population.