In general, gray matter heterotopia is fixed in both its occurrence and symptoms; that is, once symptoms occur, it does not tend to progress. Varying results from surgical resection of the affected area have been reported. Although such surgery cannot reverse developmental disabilities, it may provide full or partial relief from seizures.

Heterotopia are most commonly isolated anomalies, but may be part of a number of syndromes, including chromosomal abnormalities and fetal exposure to toxins (including alcohol).

Gray matter heterotopia (singular "heterotopion") is a neurological disorder caused by clumps of grey matter (ectopic nodules of neurons) located in the wrong part of the brain. It is characterized as a type of cortical dysplasia. The neurons in heterotopia appear to be normal, except for their mislocation; nuclear studies have shown glucose metabolism equal to that of normally positioned gray matter. The condition causes a variety of symptoms, but usually includes some degree of epilepsy or recurring seizures, and often affects the brain's ability to function on higher levels. Symptoms range from nonexistent to profound; the condition is occasionally discovered by brain imaging performed for an unrelated problem and has no apparent ill effect on the patient. At the other extreme, heterotopia can result in severe seizure disorder, loss of motor skills, and mental retardation. Fatalities are practically unknown, other than the death of unborn male fetuses with a specific genetic defect.

Because pachygyria is a structural defect no treatments are currently available other than symptomatic treatments, especially for associated seizures. Another common treatment is a gastrostomy (insertion of a feeding tube) to reduce possible poor nutrition and repeated aspiration pneumonia.

The term 'pachygyria' does not directly relate to a specific malformation but rather is used to generally describe physical characteristics of the brain in association with several neuronal migration disorders; most commonly disorders relating to varied degrees of lissencephaly. Lissencephaly is present in 1 of 85,470 births and the life span of those affected is short as only a few survive past the age of 20.

Pachygyria is a condition identified by a type of cortical genetic malformation. Clinicians will subjectively determine the malformation based on the degree of malposition and the extent of thickened abnormal grey differentiation present.

Nasal glial heterotopia is rare, while an encephalocele is uncommon. NGH usually presents in infancy, while encephalocele may present in older children and adults. It is seen in both genders equally.

While nasal glial heterotopia (NGH) is the preferred term, synonyms have included nasal glioma. However, this term is to be discouraged, as it implies a neoplasm or tumor, which it is not. By definition, nasal glial heterotopia is a specific type of choristoma. It is not a teratoma, however, which is a neoplasm comprising all three germ cell layers (ectoderm, endoderm, mesoderm). As a congenital malformation or ectopia, it is distinctly different from the trauma or iatrogenic development of an encephalocele.

The reported incidence of constriction ring syndrome varies from 1/1200 and 1/15000 live births. The prevalence is equally in male and female.

Fetomaternal factors like prematurity, maternal illnes, low birth weight and maternal drug exposure are predisposing factors for the constriction ring syndrome.

No positive relationship between CRS and genetic inheritance has been reported.

While only a few adults have been reported with 2q37 microdeletion syndrome, it is predicted that this number will rise as various research studies continue to demonstrate that most with the disorder do not have a shortened life span.

In medicine, heterotopia is the presence of a particular tissue type at a non-physiological site, but usually co-existing with original tissue in its correct anatomical location. In other words, it implies ectopic tissue, in addition to retention of the original tissue type. In neuropathology, for example, gray matter heterotopia is the presence of gray matter within the cerebral white matter or ventricles. Heterotopia within the brain is often divided into three groups: subependymal heterotopia, focal cortical heterotopia and band heterotopia. Another example is a Meckel's diverticulum, which may contain heterotopic gastric or pancreatic tissue.

In biology specifically, "heterotopy" refers to an altered location of trait expression. In her book "Developmental Plasticity and Evolution", Mary-Jane West Eberhard has a cover art of the sulphur crested cockatoo and comments on the back cover "Did long crest[head] feathers evolve by gradual modification of ancestral head feathers? Or are they descendants of wing feathers, developmentally transplanted onto the head". This idea sets the tone for the rest of her book which goes into depth about developmental novelties and their relation to evolution. Heterotopy is a somewhat obscure but well demonstrated example of how developmental change can lead to novel forms. The central concept is that a feature seen in one area of an organism has had its location changed in evolutionary lineages.

Cortical pseudolaminar necrosis, also known as cortical laminar necrosis and simply laminar necrosis, is the (uncontrolled) death of cells in the (cerebral) cortex of the brain in a band-like pattern, with a relative preservation of cells immediately adjacent to the meninges.

It is seen in the context of cerebral hypoxic-ischemic insults, i.e. strokes.

Dysmelia can be caused by

- inheritance of abnormal genes, e.g. polydactyly, ectrodactyly or brachydactyly, symptoms of deformed limbs then often occur in combination with other symptoms (syndromes)

- external causes during pregnancy (thus not inherited), e.g. via amniotic band syndrome

- teratogenic drugs (e.g. thalidomide, which causes phocomelia) or environmental chemicals

- ionizing radiation (nuclear weapons, radioiodine, radiation therapy)

- infections

- metabolic imbalance

Amniotic banding affects approximately 1 in 1,200 live births. It is also believed to be the cause of 178 in 10,000 miscarriages. Up to 50% of cases have other congenital anomalies including cleft lip, cleft palate, and clubfoot deformity. Hand and finger anomalies occur in up to 80%.

Amniotic band syndrome is considered an accidental event and it does not appear to be genetic or hereditary, so the likelihood of it occurring in another pregnancy is remote. The cause of amnion tearing is unknown and as such there are no known preventative measures.

There are three different theories to the cause of the constriction ring syndrome.

The first is the intrinsic theory, which was proposed by Streeter in 1930, implicates an anomaly in germ plasm resulting in the defects. This theory is reinforced by the clinical presentation of the constriction rings with other internal visceral and systematic anomalies. Because of these other anomalies the names “Constriction Ring Syndrome”, “Constriction Band Syndrome” and “Streeter Bands” are given to this defect/disease.

The second theory postulates the involvement of an intrauterine disruption during pregnancy followed by a cascade of events involving amniotic rupture. When spontaneous rupture of the amnion occurs early in the second trimester, the separation of amnion from chorion produces many small, thin strands that can become entangled within digits and toes.

The names “Amniotic Band Syndrome”, “Amniotic Disruption Complex", "Amniochorionic Mesoblastic Fibrous Strings", are based on this theory.

The third theory postulates the involvement of intrauterine trauma. Intrauterine trauma could be something like amniocentesis, or something like an fetal surgery. An intrauterine trauma could result in hemorrhage leading to acrosyndactyly. One study also showed the presence of bands as confirmed by sonography after fetal surgery.

Because of these different theories, there are many names for this syndrome. For a long time people believed the second theory about the amniotic rupture and strands. In the research cases not every child had a real (amniotic) strand. It could be that there has to be another explanation for the development of these anomalies.

It can occur in a number of situations which include:

- Amniotic band syndrome : particularly if unilateral

- Cornelia de Lange Syndrome

- Fetal hydantoin syndrome

- Incontinentia pigmenti

Choristomas, forms of heterotopia, are closely related benign tumors, found in abnormal locations.

It is different from hamartoma. The two can be differentiated as follows: a hamartoma is disorganized overgrowth of tissues in their normal location, (eg, Peutz-Jeghers polyps) while a choristoma is normal tissue growth in an abnormal location (e.g., gastric tissue located in distal ileum in Meckel diverticulum).

Affected individuals have a somewhat shortened lifespan. The maximum described lifespan is 67 years. Adults with 13q deletion syndrome often need support services to maintain their activities of daily living, including adult day care services or housing services.

Studies suggest that prenatal care for mothers during their pregnancies can prevent congenital amputation. Knowing environmental and genetic risks is also important. Heavy exposure to chemicals, smoking, alcohol, poor diet, or engaging in any other teratogenic activities while pregnant can increase the risk of having a child born with a congenital amputation. Folic acid is a multivitamin that has been found to reduce birth defects.

The exact cause of congenital amputation is unknown and can result from a number of causes. However, most cases show that the first three months in a pregnancy are when most birth defects occur because that is when the organs of the fetus are beginning to form. One common cause is amniotic band syndrome, which occurs when the inner fetal membrane (amnion) ruptures without injury to the outer membrane (chorion). Fibrous bands from the ruptured amnion float in the amniotic fluid and can get entangled with the fetus, thus reducing blood supply to the developing limbs to such an extent that the limbs can become strangulated; the tissues die and are absorbed into the amniotic fluid. A baby with congenital amputation can be missing a portion of a limb or the entire limb, which results in the complete absence of a limb beyond a certain point where only a stump is left is known as transverse deficiency or amelia. When a specific part is missing, it is referred to as longitudinal deficiency. Finally, phocomelia occurs when only a mid-portion of a limb is missing; for example when the hands or feet are directly attached to the trunk of the body.

Amnion ruptures can be caused by:

- teratogenic drugs (e.g. thalidomide, which causes phocomelia), or environmental chemicals

- ionizing radiation (atomic weapons, radioiodine, radiation therapy)

- infections

- metabolic imbalance

- trauma

Congenital amputation is the least common reason for amputation, but it is projected that one in 2000 babies are born each year with a missing or deformed limb. During certain periods in history, an increase in congenital amputations has been documented. One example includes the thalidomide tragedy that occurred in the 1960s when pregnant mothers were given a tranquilizer that contained the harmful drug, which produced an increase in children born without limbs. Another example was the 1986 Chernobyl catastrophe in Ukraine, where the radiation exposure caused many children to be born with abnormal or missing limbs .

2q37 deletion syndrome is a disorder caused by the deletion of a small piece of chromosome 2.2q37 deletion syndrome describes a disorder in which one or multiple of 3 sub-bands, 2q37.1, 2q37.2, and 2q37.3, of the last band of one of the chromosome 2’s long arms are deleted. The first report of this disorder was in 1989.

Trisomy 22 is a chromosomal disorder in which there are three copies of chromosome 22 rather than two. It is a frequent cause of spontaneous abortion during the first trimester of pregnancy. Progression to the second trimester and live birth are rare. This disorder is found in individuals with an extra copy or a variation of chromosome 22 in some or all cells of their body. There are many kinds of disorders associated with Trisomy 22:

Emanuel Syndrome is named after the genetic contributions made by researcher Dr. Beverly Emanuel. This condition is assigned to individuals born with an unbalanced 11/22 translocation. That is, a fragment of chromosome 11 is moved, or translocated, to chromosome 22.

22q11 Deletion Syndrome is a rare condition which occurs in approximately 1 in 4000 births. This condition is identified when a band in the q11.2 section of the arm of chromosome 22 is missing or deleted. This condition has several different names: 22q11.2 Deletion Syndrome, Velocardiofacial syndrome, DiGeorge Syndrome, Conotruncal Anomaly Face syndrome, Opitz G/BBB Syndrome, and Cayler Cardiofacial Syndrome. The effects of this disorder are different in each individual but similarities exist such as heart defects, immune system problems, a distinctive facial appearance, learning challenges, cleft palate, hearing loss, kidney problems, hypocalcemia, and sometimes psychiatric issues.

22q11 microduplication syndrome is the opposite of the 22q11 deletion syndrome: in this condition, a band of q.11.2 section of chromosome 22 is duplicated. Individuals carrying this deficiency are relatively “normal” as in they don’t possess any major birth defects or major medical illnesses. This microduplication is more common than the deletion; this might be due to the milder phenotype of the individuals.

Phelan-McDermid Syndrome / 22q13 Deletion Syndrome is a condition caused by the deletion of the tip of the q arm on chromosome 22. Most individuals with this disorder experience cognitive delays; low muscle tone; and sleeping, eating, and behavioural issues.

Chromosome Ring 22 is a rare disorder caused by the break and re-join of both ends of chromosome 22, forming a ring. The effects on the individual with this disorder are dependent on the amount of genetic information lost during the break/re-join. Major characteristics for this disorder are intellectual disability, muscle weakness and lack of coordination.

Cat Eye Syndrome / Schmid Fraccaro Syndrome is a condition caused by a partial trisomy or tetrasomy in chromosome 22. A small extra chromosome is found, made up of the top half of chromosome 22 and a portion of the q arm at the q11.2 break. This chromosome can be found three or four times. This syndrome is referred as “Cat Eye” due to the eye appearance of reported affected individuals who have coloboma of the iris; however, this feature is only seen in about half of the cases.

Mosaic trisomy 22 is a disorder in which an extra chromosome 22 is found only in some cells of the body. The severity of each case is determined by the number of cells with this extra copy. Some characteristics of individuals with this condition are cardiac abnormalities, growth retardation, mental delay, etc.

Complete Trisomy 22 is in contrast with Mosaic trisomy 22; this disorder is characterized by an extra copy of chromosome 22 which is found in each cell of the body of the affected individual. These cases are very rare, and most of the affected individuals die before birth or shortly after.

13q deletion syndrome is a rare genetic disease caused by the deletion of some or all of the large arm of human chromosome 13. It causes intellectual disability and congenital malformations that affect a variety of organ systems.

Diastematomyelia (occasionally diastomyelia) is a congenital disorder in which a part of the spinal cord is split, usually at the level of the upper lumbar vertebra.

Diastematomyelia is a rare congenital anomaly that results in the "splitting" of the spinal cord in a longitudinal (sagittal) direction. Females are affected much more commonly than males. This condition occurs in the presence of an osseous (bone), cartilaginous or fibrous septum in the central portion of the spinal canal which then produces a complete or incomplete sagittal division of the spinal cord into two hemicords. When the split does not reunite distally to the spur, the condition is referred to as a diplomyelia, or true duplication of the spinal cord.

Lisch epithelial corneal dystrophy (LECD), also known as band-shaped and whorled microcystic dystrophy of the corneal epithelium, is a rare form of corneal dystrophy first described in 1992 by Lisch et al. In one study it was linked to chromosomal region Xp22.3, with as yet unknown candidate genes.

The main features of this disease are bilateral or unilateral gray band-shaped and feathery opacities. They sometimes take on a form of a whirlpool, repeating the known pattern of corneal epithelium renewal. Abrasion of the epithelium in 3 patients brought only temporary relief, with abnormal epithelium regrowth in several months.

Epithelial cells in the zones of opacity were shown to have diffuse cytoplasmic vacuoles with as yet unestablished content.

BPES is very rare: only 50-100 cases have been described. It affects slightly more males than females.