Biliary atresia seems to affect females slightly more often than males, and Asians and African Americans more often than Caucasians. It is common for only one child in a pair of twins or within the same family to have the condition. There seems to be no link to medications or immunizations given immediately before or during pregnancy. Diabetes during pregnancy particularly during the first trimester seems to predispose to a number of distinct congenital abnormalities in the infant such as sacral agenesis and the syndromic form of biliary atresia.

The most common cause of non-duodenal intestinal atresia is a vascular accident in utero that leads to decreased intestinal perfusion and ischemia of the respective segment of bowel. This leads to narrowing, or in the most severe cases, complete obliteration of the intestinal lumen.

In the case that the superior mesenteric artery, or another major intestinal artery, is occluded, large segments of bowel can be entirely underdeveloped. Classically, the affected area of bowel assumes a spiral configuration and is described to have an "apple peel" like appearance; this is accompanied by lack of a dorsal mesentery.

Ileal atresia can also result as a complication of meconium ileus.

Fetal and neonatal intestinal atresia are treated using laparotomy after birth. If the area affected is small, the surgeon may be able to remove the damaged portion and join the intestine back together. In instances where the narrowing is longer, or the area is damaged and cannot be used for period of time, a temporary stoma may be placed.

It can be grouped into NID A and NID B, with the "A" form affecting the sympathetic innervation, and the "B" version affecting the parasympathetic innervation.

In 2002 Martucciello G et al. published the first analysis of associated anomalies in IND population is an important clinical approach to investigate possible pathogenetic correlations. Two recessive syndromes were identified (3 families). The first was characterized by NID B, intestinal malrotation, and congenital short bowel, the second by NID B, short stature, mental retardation, and facial dysmorphism. In this study, gastrointestinal anomalies accounted for 67.4% of all associated disorders. These data suggest a strong correlation between IND and intestinal development.

Intestinal neuronal dysplasia (or neuronal intestinal dysplasia or NID) is an inherited disease of the intestine that affects one in 3000 children and adults. The intestine uses peristalsis to push its contents toward the anus; IND sufferers have a problem with the motor neurons that lead to the intestine, inhibiting this process and thus preventing digestion.

It can often be confused for Hirschsprung's disease, as both have similar symptoms.

There is no cure for short bowel syndrome except transplant. In newborn infants, the 4-year survival rate on parenteral nutrition is approximately 70%. In newborn infants with less than 10% of expected intestinal length, 5 year survival is approximately 20%. Some studies suggest that much of the mortality is due to a complication of the total parenteral nutrition (TPN), especially chronic liver disease. Much hope is vested in Omegaven, a type of lipid TPN feed, in which recent case reports suggest the risk of liver disease is much lower.

Although promising, small intestine transplant has a mixed success rate, with postoperative mortality rate of up to 30%. One-year and 4-year survival rate are 90% and 60%, respectively.

Most (>95%) infants with biliary atresia will undergo an operation designed to retain and salvage the native liver, restore bile flow and reduce the level of jaundice. This is known as the Kasai procedure (after Morio Kasai, the Japanese surgeon who first developed the technique) or hepatoportoenterostomy. Although the procedure is not thought of as curative, it may relieve jaundice, and stop liver fibrosis allowing normal growth and development. Published series from Japan, North America and the UK show that bilirubin levels will fall to normal values in about 50-55% of infants allowing 40-50% to retain their own liver to reach the age of 5 and 10 years (and beyond). Liver transplantation is an option for those children whose liver function and symptoms fail to respond to a Kasai operation.

Recent large-scale studies by Davenport et al. ("Annals of Surgery", 2008) show that the age of the patient is not an absolute clinical factor affecting prognosis. The influence of age differs according to the disease etiology—i.e., whether biliary atresia is isolated, cystic (CBA), or accompanied by splenic malformation (BASM).

It is widely accepted that corticosteroid treatment after a Kasai operation, with or without choleretics and antibiotics, has a beneficial effect on postoperative bile flow and can clear jaundice, but the dosing and duration of the ideal steroid protocol are controversial. Furthermore, it has been observed in many retrospective longitudinal studies that corticosteroid treatment does not prolong survival of the native liver or transplant-free survival. Davenport et al. also showed ("Hepatology" 2007) that short-term, low-dose steroid therapy following a Kasai operation had no effect on the mid- or long-term prognosis of biliary atresia patients.

Patients with abnormal cardiac and kidney function may be more at risk for hemolytic uremic syndrome

According to a 1984 study conducted in Maryland, Hirschsprung's disease appears in 18.6 per 100,000 live births. In Japan, it occurs at a similar rate of about one in 5,000 births (20 per 100,000). It is more common in male than female (4.32:1) and in white rather than nonwhite. Nine percent of the Hirschsprung cases were also diagnosed as having Down syndrome. Most cases are diagnosed before the patient is 10 years of age.

With early intervention, morbidity and mortality of cases of intestinal obstruction is low. The outcome is in part dependent upon congenital comorbidities and delays in diagnosis and management.

The incidence of VACTERL association is estimated to be approximately 1 in 10,000 to 1 in 40,000 live-born infants. It is seen more frequently in infants born to diabetic mothers. While most cases are sporadic, there are clearly families who present with multiple involved members.

The disorder may occur by itself or in association with other genetic disorders such as Down syndrome. About half of isolated cases are linked to a specific genetic mutation and about 20% occur within families. Some of these occur in an autosomal dominant manner. The cause of the remaining cases is unclear. If otherwise normal parents have one child with the condition, the next child has a 4% risk of being affected.

Short bowel syndrome in adults and children is usually caused by surgery. This surgery may be done for:

- Crohn's disease, an inflammatory disorder of the digestive tract

- Volvulus, a spontaneous twisting of the small intestine that cuts off the blood supply and leads to tissue death

- Tumors of the small intestine

- Injury or trauma to the small intestine

- Necrotizing enterocolitis (premature newborn)

- Bypass surgery to treat obesity

- Surgery to remove diseases or damaged portion of the small intestine

Some children are also born with an abnormally short small intestine, known as congenital short bowel.

Umbilical cord ulceration and intestinal atresia is a rare congenital disease that leads to intestinal atresia, umbilical cord ulceration and severe intrauterine haemorrhage. Only 15 cases have so far been reported, though newer studies are beginning to conclude that this disease has a higher incidence rate than has been previously reported. A particular study has given intestinal atresia and umbilical cord ulceration a clear link after 5 such cases were reported at the time of publication.

Microvillus inclusion disease is thought to be extremely rare; only approximately 200 cases have been identified in children in Europe.

One patient, a teenage female living in Arizona, suddenly began to grow microvilli after thirteen years of TPN (Total Parenteral Nutrition) and Lipid dependency. She now enjoys a typical teenage diet and is seen regularly by her Gastroenterologist.

One patient from the UK was documented to achieve nutritional independence at age 3.

On 26 June 2009 a six-year-old girl diagnosed with microvillus inclusion disease became the third person in the UK to die of swine flu.

It is nearly always fatal unless, like short bowel syndrome patients, treated with parenteral nutrition or an intestinal transplant. The patient is often classified as being in "intestinal failure" and treated with the cohort of patients known as "short bowel syndrome" patients.

Atresia is a condition in which an orifice or passage in the body is (usually abnormally) closed or absent.

Examples of atresia include:

- Biliary atresia, a condition in newborns in which the common bile duct between the liver and the small intestine is blocked or absent.

- Choanal atresia, blockage of the back of the nasal passage, usually by abnormal bony or soft tissue.

- Esophageal atresia, which affects the alimentary tract and causes the esophagus to end before connecting normally to the stomach.

- Imperforate anus, malformation of the opening between the rectum and anus.

- Intestinal atresia, malformation of the intestine, usually resulting from a vascular accident in utero.

- Microtia, absence of the ear canal or failure of the canal to be tubular or fully formed (can be related to Microtia, a congenital deformity of the pinna, or outer ear).

- Ovarian follicle atresia, the degeneration and subsequent resorption of one or more immature ovarian follicles.

- Potter sequence, congenital decreased size of the kidney leading to absolutely no functionality of the kidney, usually related to a single kidney.

- Pulmonary atresia, malformation of the pulmonary valve in which the valve orifice fails to develop.

- Renal agenesis, only having one kidney.

- Tricuspid atresia, a form of congenital heart disease whereby there is a complete absence of the tricuspid valve, and consequently an absence of the right atrioventricular connection.

- Vaginal atresia, a congenital occlusion of the vagina or subsequent adhesion of the walls of the vagina, resulting in its occlusion.

The diagnosis is suspected based on polyhydramnios in uteru, bilious vomiting, failure to pass meconium in the first day of life, and abdominal distension. The presentations of NBO may vary. It may be subtle and easily overlooked on physical examination or can involve massive abdominal distension, respiratory distress and cardiovascular collapse. Unlike older children, neonates with unrecognized intestinal obstruction deteriorate rapidly.

The incidence of the mutation is between 1 in 10,000 and 1 in 15,000 births.

By age 35 years, 95% of individuals with FAP (>100 adenomas) have polyps. Without colectomy, colon cancer is virtually inevitable. The mean age of colon cancer in untreated individuals is 39 years (range 34–43 years).

Attentuated FAP arises when APC is defective but still somewhat functional. As a result, it retains part of its ability to suppress polyps. Therefore, attenuated FAP manifests as colorectal cancer unusually late (age 40–70, average=55), and typically with few, or at least far fewer polyps (typically 30), than the more usual version of FAP, at an age when FAP is no longer considered much of a likelihood or risk according to usual FAP epidemiology.

Laparotomy for other forms of volvulus, especially anal volvulus.

Congenital chloride diarrhea (CCD, also congenital chloridorrhea or Darrow Gamble syndrome) is a genetic disorder due to an autosomal recessive mutation on chromosome 7. The mutation is in downregulated-in-adenoma (DRA), a gene that encodes a membrane protein of intestinal cells. The protein belongs to the solute carrier 26 family of membrane transport proteins. More than 20 mutations in the gene are known to date. A rare disease, CCD occurs in all parts of the world but is more common in some populations with genetic founder effects, most notably in Finland.

Observations leading to the characterization of the SLC26 family were based on research on rare human diseases. Three rare recessive diseases in humans have been shown to be caused by genes of this family. Diastrophic dysplasia, congenital chloride diarrhea, and Pendred syndrome are caused by the highly related genes SLC26A2 (first called DTDST), SLC26A3 (first called CLD or DRA), and SLC26A4 (first called PDS), respectively. Two of these diseases, diastrophic dysplasia and congenital chloride diarrhea, are Finnish heritage diseases.

There are frequent associated congenital anomalies all related to deviations in the development of anatomical asymmetries in early embryonic stages. These conditions considered together are called "polysplenia syndrome".

Associated conditions include heterotaxy syndrome, intestinal malrotation, situs inversus, biliary atresia, and several cardiac malformations. Associated cardiac conditions include dextrocardia, atrial situs ambiguus, ventricular inversion, and VA concordance with left posterior aorta.

Although present, the multiple small spleens are often ineffective; this is termed functional asplenia.

Polysplenia or Chaudhrey's disease is a congenital disease manifested by multiple small accessory spleens, rather than a single, full-sized, normal spleen. Polysplenia sometimes occurs alone, but it is often accompanied by other developmental abnormalities. Conditions associated with polysplenia include gastrointestinal abnormalities, such as intestinal malrotation or biliary atresia, as well as cardiac abnormalities, such as dextrocardia.

Known environmental factors include certain infections during pregnancy such as Rubella, drugs (alcohol, hydantoin, lithium and thalidomide) and maternal illness (diabetes mellitus, phenylketonuria, and systemic lupus erythematosus).

Being overweight or obese increases the risk of congenital heart disease. Additionally, as maternal obesity increases, the risk of heart defects also increases. A distinct physiological mechanism has not been identified to explain the link between maternal obesity and CHD, but both prepregnancy folate deficiency and diabetes have been implicated in some studies.