Ring chromosome 14 syndrome is extremely rare, the true rate of occurrence is unknown (as it is "less than" 1 per 1,000,000), but there are at least 50 documented cases in the literature.

The true prevalence of PMS has not been determined. More than 1200 people have been identified worldwide according the Phelan-McDermid Syndrome Foundation. However, it is believed to be underdiagnosed due to inadequate genetic testing and lack of specific clinical features. It is known to occur with equal frequency in males and females. Studies using chromosomal microarray for diagnosis indicate that at least 0.5% of cases of ASD can be explained by mutations or deletions in the "SHANK3" gene. In addition when ASD is associated with ID, "SHANK3" mutations or deletions have been found in up to 2% of individuals.

Miller-Dieker occurs in less than one in 100000 people and can occur in all races.

Trisomy 8 mosaicism affects wide areas of chromosome 8 containing many genes, and can thus be associated with a range of symptoms.

- Mosaic trisomy 8 has been reported in rare cases of Rothmund-Thomson syndrome, a genetic disorder associated with the DNA helicase RECQL4 on chromosome 8q24.3. The syndrome is "characterized by skin atrophy, telangiectasia, hyper- and hypopigmentation, congenital skeletal abnormalities, short stature, premature aging, and increased risk of malignant disease".

- Some individuals trisomic for chromosome 8 were deficient in production of coagulation factor VII due to a factor 7 regulation gene (F7R) mapped to 8p23.3-p23.1.

- Trisomy and other rearrangements of chromosome 8 have also been found in tricho–rhino–phalangeal syndrome.

- Small regions of chromosome 8 trisomy and monosomy are also created by recombinant chromosome 8 syndrome (San Luis Valley syndrome), causing anomalies associated with tetralogy of Fallot, which results from recombination between a typical chromosome 8 and one carrying a parental paracentric inversion.

- Trisomy is also found in some cases of chronic myeloid leukaemia, potentially as a result of karyotypic instability caused by the fusion gene.

Most individuals with this condition do not survive beyond childhood. Individuals with MDS usually die in infancy and therefore do not live to the age where they can reproduce and transmit MDS to their offspring.

Chromosomal deletion syndromes result from deletion of parts of chromosomes. Depending on the location, size, and whom the deletion is inherited from, there are a few known different variations of chromosome deletions. Chromosomal deletion syndromes typically involve larger deletions that are visible using karyotyping techniques. Smaller deletions result in Microdeletion syndrome, which are detected using fluorescence in situ hybridization (FISH)

Examples of chromosomal deletion syndromes include 5p-Deletion (cri du chat syndrome), 4p-Deletion (Wolf-Hirschhorn syndrome), Prader–Willi syndrome, and Angelman syndrome.

22q13 deletion syndrome (spoken as "twenty-two q one three", see Locus (genetics)) is a genetic disorder caused by deletions or rearrangements on the q terminal end (long arm) of chromosome 22. Any abnormal genetic variation in the q13 region that presents with significant manifestations (phenotype) typical of a terminal deletion may be diagnosed as 22q13 deletion syndrome. 22q13 deletion syndrome is often called Phelan-McDermid syndrome (abbreviated PMS). There is disagreement among researchers as to the exact definition of 22q13 deletion syndrome. The Developmental Synaptopathies Consortium defines PMS as being caused by "SHANK3" mutations, a definition that appears to exclude terminal deletions. The requirement to include "SHANK3" in the definition is supported by many, but not by those who first described 22q13 deletion syndrome.

A prototypical terminal deletion of 22q13 can be uncovered by karyotype analysis, but many terminal and interstitial deletions are too small. The availability of DNA microarray technology for revealing multiple genetic problems simultaneously has been the diagnostic tool of choice. The falling cost for whole exome sequencing and, eventually, whole genome sequencing, may replace DNA microarray technology for candidate evaluation. However, fluorescence in situ hybridization (FISH) tests remain valuable for diagnosing cases of mosaicism (mosaic genetics) and chromosomal rearrangements (e.g., ring chromosome, unbalanced chromosomal translocation). Although early researchers sought a monogenic (single gene genetic disorder) explanation, recent studies have not supported that hypothesis (see Etiology, below).

Ring chromosome 14 syndrome is a very rare human chromosome abnormality. It occurs when one or both of the telomeres that mark the ends of chromosome 14 are lost allowing the now uncapped ends to fuse together forming a ring chromosome. It causes a number of serious health issues.

Currently, research is focusing on identifying the role of the genes on 18p and 18q in causing the signs and symptoms associated with deletions of 18p and/or 18q. This will ultimately enable predictive genotyping.Thus far, several genes on chromosome 18 have been linked with a phenotypic effect.

TGIF - Mutations and deletions of this gene, which is located on18p, have been associated with holoprosencephaly. Penetrance is incomplete, meaning that a deletion of one copy of this gene is not in and of itself sufficient to cause holoprosencephaly. Ten to fifteen percent of people with 18p- have holoprosencephaly, suggesting that other genetic and environmental facts play a role in the etiology of holoprosencephaly in these individuals.

TCF4 – In 2007, deletions of or point mutations in this gene, which is located on 18q, were identified as the cause of Pitt-Hopkins disease. This is the first gene that has been definitively shown to directly cause a clinical phenotype when deleted. If a deletion includes the TCF4 gene (located at 52,889,562-52,946,887), features of Pitt-Hopkins may be present, including abnormal corpus callosum; short neck; small penis; accessory and wide-spaced nipples; broad or clubbed fingers; and sacral dimple. Those with deletions inclusive of TCF4 have a significantly more severe cognitive phenotype.

TSHZ1 - Point mutations and deletions of this gene, located on 18q, are linked with congenital aural atresia Individuals with deletions inclusive of this gene have a 78% chance of having aural atresia.

"Critical regions" – Recent research has narrowed the critical regions for four features of the distal 18q- phenotype down to a small segment of distal 18q, although the precise genes responsible for those features remain to be identified.

"Haplolethal Regions" - There are two regions on chromosome 18 that has never been found to be deleted. They are located between the centromere and 22,826,284 bp (18q11.2) and between 43,832,732 and 45,297,446 bp (18q21.1). It is hypothesized that there are genes in these regions that are lethal when deleted.

Respiratory complications are often cause of death in early infancy.

Raine syndrome (RNS), also called osteosclerotic bone dysplasia, is a rare autosomal recessive congenital disorder characterized by craniofacial anomalies including microcephaly, noticeably low set ears, osteosclerosis, a cleft palate, gum hyperplasia, a hypoplastic nose, and eye proptosis. It is considered to be a lethal disease, and usually leads to death within a few hours of birth. However, a recent report describes two studies in which children with Raine Syndrome have lived to 8 and 11 years old, so it is currently proposed that there is a milder expression that the phenotype can take (Simpson 2009).

It was first characterized in 1989 in a report that was published on an infant that had been born with an unknown syndrome, that later came to be called Raine Syndrome.

The current research describes Raine Syndrome as a neonatal osteosclerotic bone dysplasia, indicated by its osteosclerotic symptoms that are seen in those suffering from the disease. It has been found that a mutation in the gene FAM20C is the cause of the Raine Syndrome phenotype. This microdeletion mutation leads to an unusual chromosome 7 arrangement. The milder phenotypes of Raine Syndrome, such as those described in Simpson’s 2007 report, suggest that Raine Syndrome resulting from missense mutations may not be as lethal as the other described mutations (OMIM). This is supported by findings from Fradin et al. (2011), who reported on children with missense mutations to FAM20C and lived to ages 1 and 4 years, relatively much longer than the life spans of the previously reported children. Simpson et al.’s (2007) report states that to date, effected individuals have had chromosome 7 uniparental isodisomy and a 7p telomeric microdeletion. They had abnormal chromosome 7 arrangements, with microdeletions of their D7S2477 and D7S1484 markers (Simpson 2007).

Raine Syndrome appears to be an autosomal recessive disease. There are reports of recurrence in children born of the same parents, and an increased occurrence in children of closely related, genetically similar parents. Individuals with Raine Syndrome were either homozygous or compound heterozygous for the mutation of FAM20C. Also observed have been nonsynonomous mutation and splice-site changes (Simpson et al. 2007).

FAM20C, located on chromosome 7p22.3, is an important molecule in bone development. Studies in mice have demonstrated its importance in the mineralization of bones in teeth in early development (OMIM, Simpson et al. 2007, Wang et al. 2010). FAM20C stands for “family with sequence similarity 20, member C.” It is also commonly referred to as DMP-4. It is a Golgi-enriched fraction casein kinase and an extracellular serine/threonine protein kinase. It is 107,743 bases long, with 10 exons and 584 amino acids (Weizmann Institute of Science).

Marshall–Smith syndrome is not to be confused with:

- Marshall syndrome (aka.Periodic fever, aphthous stomatitis, pharyngitis and adenitis (PFAPA syndrome, see also: Periodic fever syndrome)

- Sotos (like) syndrome

- Weaver-Smith syndrome (WSS)

Human genetic disorders can be caused by ring chromosome formation. Although ring chromosomes are very rare, they have been found in all human chromosomes. Symptoms seen in patients carrying ring chromosomes are more likely to be caused by the deletion of genes in the telomeric regions of affected chromosomes, rather than by the formation of a ring structure itself. Almost all ring chromosome syndromes feature marked growth delay.

Ring chromosomes can be inherited or sporadic. Mosaicism is common and affects the severity of the condition. Location of fusion also affects severity due to loss of differing amounts of genetic material from the ends of chromosomes.

Disorders arising from the formation of a ring chromosome include:

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.

Trisomy 8, also known as Warkany syndrome 2, is a human chromosomal disorder caused by having three copies (trisomy) of chromosome 8. It can appear with or without mosaicism.

Revesz syndrome has so far been observed only in children. There is not much information about the disease because of its low frequency in general population and under reporting of cases.

The estimated prevalence of Jacobsen syndrome is believed to be approximately 1 out of every 100,000 births. For reasons unknown females are twice as likely to have Jacobsen Syndrome than males. No preference for any race or ethnicity has been reported so far.

A ring chromosome is an aberrant chromosome whose ends have fused together to form a ring. Ring chromosomes were first discovered by Lilian Vaughan Morgan in 1926. A ring chromosome is denoted by the symbol "r" in human genetics and "R" in Drosophila genetics. Ring chromosomes may form in cells following genetic damage by mutagens like radiation, but they may also arise spontaneously during development.

Jacobsen Syndrome is a rare chromosomal disorder resulting from deletion of genes from chromosome 11 that includes band 11q24.1. It is a congenital disorder. Since the deletion takes place on the q arm of chromosome 11, it is also called 11q terminal deletion disorder. The deletion may range from 5 million to 16 million deleted DNA base pairs. The severity of symptoms depends on the number of deletions. The more deletions there are more severe the symptoms are likely to be. People with Jacobsen syndrome have serious intellectual disabilities, dysmorphic features, delayed development and a variety of physical problems including heart defects. Research shows that almost 88.5% of people with Jacobsen Syndrome have a bleeding disorder called Paris-Trousseau syndrome. [ Jacobsen Syndrome is catastrophic in 1 out of every 5 cases, since children usually die within the first 2 years of life due to heart complications.

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.

Ring 18 is a genetic condition caused by a deletion of the two tips of chromosome 18 followed by the formation of a ring-shaped chromosome. It was first reported in 1964.

Ring chromosome 20, ring-shaped chromosome 20 or r(20) syndrome is a rare human chromosome abnormality where the two arms of chromosome 20 fuse to form a ring chromosome. The syndrome is associated with epileptic seizures, behaviour disorders and mental retardation.

When not all cells contain a ring chromosome 20, the individual suffers from ring 20 chromosomal mosaicism.Ring Chromosome 20 syndrome is thought to be an underdiagnosed condition. Since chromosomal analysis or karyotype testing is not a routine investigation for patients with epilepsy, the diagnosis of ring chromosome 20 syndrome is typically delayed or unrecognized.

Its exact cause is unknown, but present research points toward a genetic component, possibly following maternal genes.

It involves hypomethylation of "H19" and "IGF2". In 10% of the cases the syndrome is associated with maternal uniparental disomy (UPD) on chromosome 7. This is an imprinting error where the person receives two copies of chromosome 7 from the mother (maternally inherited) rather than one from each parent.

Like other imprinting disorders (e.g. Prader–Willi syndrome, Angelman syndrome, and Beckwith–Wiedemann syndrome), Silver–Russell syndrome may be associated with the use of assisted reproductive technologies such as in vitro fertilization.

This disorder is caused by the deletion of the long arm of chromosome 13, which can either be deleted linearly or as a ring chromosome. It is typically not hereditary—the loss of a portion of the chromosome typically occurs during gametogenesis, making it a de novo mutation. When it is hereditary, it is usually caused by a parent having mosaicism or a balanced translocation.

The severity of the disorder is correlated with the size of the deletion, with larger deletions causing more severe manifestations.

Greig cephalopolysyndactyly syndrome is a chromosomal condition related to chromosome 7. Mutations in the "GLI3" gene cause Greig cephalopolysyndactyly syndrome. The "GLI3" gene provides instructions for making a protein that controls gene expression, which is a process that regulates whether genes are turned on or off in particular cells. By interacting with certain genes at specific times during development, the "GLI3" protein plays a role in the normal shaping (patterning) of many organs and tissues before birth.

Different genetic changes involving the "Gli3" gene can cause Greig cephalopolysyndactyly syndrome. In some cases, the condition results from a chromosomal abnormality, such as a large deletion or translocation of genetic material, in the region of chromosome 7 that contains the GLI3 gene. In other cases, a mutation in the GLI3 gene itself is responsible for the disorder. Each of these genetic changes prevents one copy of the gene in each cell from producing any functional protein. It remains unclear how a reduced amount of this protein disrupts early development and causes the characteristic features of Greig cephalopolysyndactyly syndrome.

This condition is inherited in an autosomal dominant pattern, which means the defective gene is located on an autosome, and only one copy of the defective GLI3 gene is sufficient to cause the disorder. In cases of dominant inheritance, an affected person inherits the genetic mutation or chromosomal abnormality from one affected parent.

Rare instances of this disorder are sporadic, and occur in people with no history of the condition in their family.