
Bannayan–Riley–Ruvalcaba syndrome (BRRS) is a rare overgrowth syndrome and hamartomatous disorder with occurrence of multiple subcutaneous lipomas, macrocephaly and hemangiomas. The disease is inherited in an autosomal dominant manner. The disease belongs to a family of hamartomatous polyposis syndromes, which also includes Peutz–Jeghers syndrome, juvenile polyposis and Cowden syndrome. Mutation of the PTEN gene underlies this syndrome, as well as Cowden syndrome, Proteus syndrome, and Proteus-like syndrome, these four syndromes are referred to as PTEN Hamartoma-Tumor Syndromes.

Berdon syndrome, also called Megacystis-microcolon-intestinal hypoperistalsis syndrome, is an autosomal recessive fatal genetic disorder affecting newborns. In a 2011 study of 227 children with the syndrome, "the oldest survivor [was] 24 years old." The Ann Arbor News reported a five year old survivor at the end of 2015.

Blue diaper syndrome is a rare, autosomal recessive metabolic disorder characterized in infants by bluish urine-stained diapers. It is also known as Drummond's syndrome, and hypercalcemia.
Esophageal rupture is a rupture of the esophageal wall. Iatrogenic causes account for approximately 56% of esophageal perforations, usually due to medical instrumentation such as an endoscopy or paraesophageal surgery. In contrast, the term Boerhaave syndrome is reserved for the 10% of esophageal perforations which occur due to vomiting.

Carcinoid syndrome is a paraneoplastic syndrome comprising the signs and symptoms that occur secondary to carcinoid tumors. The syndrome includes flushing and diarrhea, and less frequently, heart failure, vomiting and bronchoconstriction. It is caused by endogenous secretion of mainly serotonin and kallikrein.

CDK13-related disorder, also known as congenital heart defects, dysmorphic facial features and intellectual developmental disorder (CHDFIDD), is a very rare autosomal dominant genetic condition characterised by congenital heart defects, intellectual disability and characteristic facial features. Those affected typically have motor and language delays, low muscle tone and gastrointestinal dysmotility. Facial features include a wide nasal bridge, widely-spaced eyes, prominent, low-set ears, a flat nose tip and a small mouth. Less common features include congenital spinal abnormalities, hearing loss or seizures.

Chilaiditi syndrome is a rare condition when pain occurs due to transposition of a loop of large intestine in between the diaphragm and the liver, visible on plain abdominal X-ray or chest X-ray.

Cowden syndrome is an autosomal dominant inherited condition characterized by benign overgrowths called hamartomas as well as an increased lifetime risk of breast, thyroid, uterine, and other cancers. It is often underdiagnosed due to variability in disease presentation, but 99% of patients report mucocutaneous symptoms by age 20-29. Despite some considering it a primarily dermatologic condition, Cowden's syndrome is a multi-system disorder that also includes neurodevelopmental disorders such as macrocephaly.

Cronkhite–Canada syndrome is a rare syndrome characterized by multiple polyps of the digestive tract. It is sporadic, and it is currently considered acquired and idiopathic.

Distal intestinal obstruction syndrome (DIOS) involves obstruction of the distal part of the small intestines by thickened intestinal content and occurs in about 20% of mainly adult individuals with cystic fibrosis. DIOS was previously known as meconium ileus equivalent, a name which highlights its similarity to the intestinal obstruction seen in newborn infants with cystic fibrosis. DIOS tends to occur in older individuals with pancreatic insufficiency. Individuals with DIOS may be predisposed to bowel obstruction, though it is a separate entity than true constipation.

Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual disability, and characteristic facial features. The average IQ of a young adult with Down syndrome is 50, equivalent to the mental ability of an 8- or 9-year-old child, but this can vary widely.

Dumping syndrome occurs when food, especially sugar, moves too quickly from the stomach to the duodenum—the first part of the small intestine—in the upper gastrointestinal (GI) tract. This condition is also called rapid gastric emptying. It is mostly associated with conditions following gastric or esophageal surgery, though it can also arise secondary to diabetes or to the use of certain medications; it is caused by an absent or insufficiently functioning pyloric sphincter, the valve between the stomach and the duodenum.

Feingold syndrome is a rare autosomal dominant hereditary disorder. It is named after Murray Feingold, an American physician who first described the syndrome in 1975. Until 2003, at least 79 patients have been reported worldwide.

Gardner's syndrome is a subtype of familial adenomatous polyposis (FAP). Gardner syndrome is an autosomal dominant form of polyposis characterized by the presence of multiple polyps in the colon together with tumors outside the colon. The extracolonic tumors may include osteomas of the skull, thyroid cancer, epidermoid cysts, fibromas, as well as the occurrence of desmoid tumors in approximately 15% of affected individuals.

Gastric outlet obstruction (GOO) is a medical condition where there is an obstruction at the level of the pylorus, which is the outlet of the stomach. Individuals with gastric outlet obstruction will often have recurrent vomiting of food that has accumulated in the stomach, but which cannot pass into the small intestine due to the obstruction. The stomach often dilates to accommodate food intake and secretions. Causes of gastric outlet obstruction include both benign causes, as well as malignant causes, such as gastric cancer.

Hereditary hemorrhagic telangiectasia (HHT), also known as Osler–Weber–Rendu disease and Osler–Weber–Rendu syndrome, is a rare autosomal dominant genetic disorder that leads to abnormal blood vessel formation in the skin, mucous membranes, and often in organs such as the lungs, liver, and brain.

Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome is an autosomal dominant genetic condition that is associated with a high risk of colon cancer as well as other cancers including endometrial cancer, ovary, stomach, small intestine, hepatobiliary tract, upper urinary tract, brain, and skin. The increased risk for these cancers is due to inherited mutations that impair DNA mismatch repair. It is a type of cancer syndrome.

Heyde's syndrome is a syndrome of gastrointestinal bleeding from angiodysplasia in the presence of aortic stenosis.

Irritable bowel syndrome (IBS) is a group of symptoms—including abdominal pain and changes in the pattern of bowel movements without any evidence of underlying damage. These symptoms occur over a long time, often years. It has been classified into four main types depending on whether diarrhea is common, constipation is common, both are common, or neither occurs very often. IBS negatively affects quality of life and may result in missed school or work. Disorders such as anxiety, major depression, and chronic fatigue syndrome are common among people with IBS.

Johanson–Blizzard syndrome is a rare, sometimes fatal autosomal recessive multisystem congenital disorder featuring abnormal development of the pancreas, nose and scalp, with mental retardation, hearing loss and growth failure. It is sometimes described as a form of ectodermal dysplasia.

Juvenile polyposis syndrome is an autosomal dominant genetic condition characterized by the appearance of multiple juvenile polyps in the gastrointestinal tract. Polyps are abnormal growths arising from a mucous membrane. These usually begin appearing before age 20, but the term juvenile refers to the type of polyp, not to the age of the affected person. While the majority of the polyps found in juvenile polyposis syndrome are non-neoplastic, hamartomatous, self-limiting and benign, there is an increased risk of adenocarcinoma.

Mismatch repair cancer syndrome (MMRCS) is a cancer syndrome associated with biallelic DNA mismatch repair mutations. It is also known as Turcot syndrome and by several other names.
Mowat–Wilson syndrome is a rare genetic disorder that was clinically delineated by Dr. David R. Mowat and Dr. Meredith J. Wilson in 1998.

Ogilvie syndrome is the acute dilatation of the colon in the absence of any mechanical obstruction in severely ill patients.

Okamoto syndrome (OS), also known as Au–Kline syndrome (AKS), is a very rare autosomal dominant genetic condition characterised by congenital hydronephrosis, low muscle tone, heart defects, intellectual disability and characteristic facial features. Those affected often have neurological and skeletal abnormalities, as well as frequent urinary tract infections. Language and walking are usually delayed. Facial features include prominent, downturned ears, an open, downturned mouth and drooping eyelids (ptosis).

Peutz–Jeghers syndrome is an autosomal dominant genetic disorder characterized by the development of benign hamartomatous polyps in the gastrointestinal tract and hyperpigmented macules on the lips and oral mucosa (melanosis). This syndrome can be classed as one of various hereditary intestinal polyposis syndromes and one of various hamartomatous polyposis syndromes. It has an incidence of approximately 1 in 25,000 to 300,000 births.

Plummer–Vinson syndrome is a rare disease characterized by difficulty swallowing, iron-deficiency anemia, glossitis, cheilosis and esophageal webs. Treatment with iron supplementation and mechanical widening of the esophagus generally provides an excellent outcome.

Strømme syndrome is a very rare autosomal recessive genetic condition characterised by intestinal atresia, eye abnormalities and microcephaly. The intestinal atresia is of the "apple-peel" type, in which the remaining intestine is twisted around its main artery. The front third of the eye is typically underdeveloped, and there is usually moderate developmental delay. Less common features include an atrial septal defect, increased muscle tone or skeletal abnormalities. Physical features may include short stature, large, low-set ears, a small jaw, a large mouth, epicanthic folds or fine, sparse hair.
Superior mesenteric artery (SMA) syndrome is a gastro-vascular disorder in which the third and final portion of the duodenum is compressed between the abdominal aorta (AA) and the overlying superior mesenteric artery. This rare, potentially life-threatening syndrome is typically caused by an angle of 6°–25° between the AA and the SMA, in comparison to the normal range of 38°–56°, due to a lack of retroperitoneal and visceral fat. In addition, the aortomesenteric distance is 2–8 millimeters, as opposed to the typical 10–20. However, a narrow SMA angle alone is not enough to make a diagnosis, because patients with a low BMI, most notably children, have been known to have a narrow SMA angle with no symptoms of SMA syndrome.

Townes–Brocks syndrome (TBS) is a rare genetic disease that has been described in approximately 200 cases in the published literature. It affects both males and females equally. The condition was first identified in 1972. by Philip L. Townes, who was at the time a human geneticists and Professor of Pediatrics, and Eric Brocks, who was at the time a medical student, both at the University of Rochester.

Tricho-hepato-enteric syndrome (THE), also known as syndromic or phenotypic diarrhea, is an extremely rare congenital bowel disorder which manifests itself as intractable diarrhea in infants with intrauterine growth retardation, hair and facial abnormalities. Many also have liver disease and abnormalities of the immune system. The associated malabsorption leads to malnutrition and failure to thrive.

Triple-A syndrome or AAA syndrome, is a rare autosomal recessive congenital disorder. In most cases, there is no family history of it. The syndrome was first identified by Jeremy Allgrove and colleagues in 1978, since then just over 100 cases have been reported. The syndrome involves achalasia, addisonianism, and alacrima. Alacrima is usually the earliest manifestation. It is a progressive disorder that can take years to develop the full-blown clinical picture.

Zollinger–Ellison syndrome is a disease in which tumors cause the stomach to produce too much acid, resulting in peptic ulcers. Symptoms include abdominal pain and diarrhea.