Kleefstra syndrome affects males and females equally and approximately, 75% of all documented cases are caused by Eu-HMTase1 disruptions while only 25% are caused by 9q34.3 deletions. There are no statistics on the effect the disease has on life expectancy due to the lack of information available.

Due to its recent discovery, there are currently no existing treatments for Kleefstra syndrome.

Research on the risk for developing schizophrenia in Ashkenazi Jews and other populations showed that 3q29 microdeletion syndrome leads to a significant higher rate of schizophrenia.

On several locations in the world people are studying on the subject of 1q21.1 deletion syndrome. The syndrome was identified for the first time with people with heart abnormalities. The syndrome has later been found with patients with autism and schizophrenia. Research is done on patients with a symptom of the syndrome, to find more patients with the syndrome.

There may be a relation between autism and schizophrenia. Literature shows that nine locations have been found on the DNA where the syndromes related to autism or schizophrenia can be found, the so-called "hotspots": 1q21.1, 3q29, 15q13.3, 16p11.2, 16p13.1, 16q21, 17p12, 21q11.2 and 21q13.3. With a number of hotspots both autism and schizophrenia were observed at that location. In other cases, either autism or schizophrenia has been seen.

Statistical research showed that schizophrenia is more common in combination with 1q21.1 deletion syndrome. On the other side, autism is significantly more common with 1q21.1 duplication syndrome. Further research confirmed that the odds on a relation between schizophrenia and deletions at 1q21.1, 3q29, 15q13.3, 22q11.21 en Neurexin 1 (NRXN1) and duplications at 16p11.2 are at 7.5% or higher.

Common variations in the BCL9 gene, which is in the distal area, confer risk of schizophrenia and may also be associated with bipolar disorder and major depressive disorder.

Research is done on 10–12 genes on 1q21.1 that produce DUF1220-locations. DUF1220 is an unknown protein, which is active in the neurons of the brain near the neocortex. Based on research on apes and other mammals, it is assumed that DUF1220 is related to cognitive development (man: 212 locations; chimpanzee: 37 locations; monkey: 30 locations; mouse: 1 location). It appears that the DUF1220-locations on 1q21.1 are in areas that are related to the size and the development of the brain. The aspect of the size and development of the brain is related to autism (macrocephaly) and schizophrenia (microcephaly). It has been proposed that a deletion or duplication of a gene that produces DUF1220-areas might cause growth and development disorders in the brain

Another relation between macrocephaly with duplications and microcephaly with deletions has been seen in research on the HYDIN Paralog or HYDIN2. This part of 1q21.1 is involved in the development of the brain. It is assumed to be a dosage-sensitive gene. When this gene is not available in the 1q21.1 area, it leads to microcephaly. HYDIN2 is a recent duplication (found only in humans) of the HYDIN gene found on 16q22.2.

Research on the genes CHD1L and PRKAB2 within lymphoblast cells lead to the conclusion that anomalies appear with the 1q21.1-deletionsyndrome:

- CHD1L is an enzyme which is involved in untangling the chromatides and the DNA repair system. With 1q21.1 deletion syndrome a disturbance occurs, which leads to increased DNA breaks. The role of CHD1L is similar to that of helicase with the Werner syndrome

- PRKAB2 is involved in maintaining the energy level of cells. With 1q21.1-deletion syndrome this function was attenuated.

GJA5 has been identified as the gene that is responsible for the phenotypes observed with congenital heart diseases on the 1q21.1 location. In case of a duplication of GJA5 tetralogy of Fallot is more common. In case of a deletion other congenital heart diseases than tetralogy of Fallot are more common.

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

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.

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.

Several researchers around the world are studying on the subject of 1q21.1 duplication syndrome. The syndrome was identified for the first time in people with heart abnormalities. The syndrome was later observed in patients who had autism or schizophrenia.

It appears that there is a relation between autism and schizophrenia. Literature shows that nine locations have been found on the DNA where the syndromes related to autism or schizophrenia can be found, the so-called "hotspots": 1q21.1, 3q29, 15q13.3, 16p11.2, 16p13.1, 16q21, 17p12, 21q11.2 and 21q13.3. With a number of hotspots both autism and schizophrenia were observed at that location. In other cases, either autism or schizophrenia has been seen, while they are searching for the opposite.

Statistical research showed that schizophrenia is significantly more common in combination with 1q21.1 deletion syndrome. On the other side, autism is significantly more common with 1q21.1 duplication syndrome. Similar observations were done for chromosome 16 on 16p11.2 (deletion: autism/duplication: schizophrenia), chromosome 22 on 22q11.21 (deletion (Velo-cardio-facial syndrome): schizophrenia/duplication: autism) and 22q13.3 (deletion (Phelan-McDermid syndrome): schizophrenia/duplication: autism). Further research confirmed that the odds on a relation between schizophrenia and deletions at 1q21.1, 3q29, 15q13.3, 22q11.21 en Neurexin 1 (NRXN1) and duplications at 16p11.2 are at 7.5% or higher.

Common variations in the BCL9 gene, which is in the distal area, confer risk of schizophrenia and may also be associated with bipolar disorder and major depressive disorder.

Research is done on 10-12 genes on 1q21.1 that produce DUF1220-locations. DUF1220 is an unknown protein, which is active in the neurons of the brain near the neocortex. Based on research on apes and other mammals, it is assumed that DUF1220 is related to cognitive development (man: 212 locations; chimpanzee: 37 locations; monkey: 30 locations; mouse: 1 location). It appears that the DUF1220-locations on 1q21.1 are in areas that are related to the size and the development of the brain. The aspect of the size and development of the brain is related to autism (macrocephaly) and schizophrenia (microcephaly). It is assumed that a deletion or a duplication of a gene that produces DUF1220-areas might cause growth and development disorders in the brain

Another relation between macrocephaly with duplications and microcephaly with deletions has been seen in research on the HYDIN Paralog or HYDIN2. This part of 1q21.1 is involved in the development of the brain. It is assumed to be a dosage-sensitive gene. When this gene is not available in the 1q21.1 area it leads to microcephaly. HYDIN2 is a recent duplication (found only in humans) of the HYDIN gene found on 16q22.2.

GJA5 has been identified as the gene that is responsible for the phenotypes observed with congenital heart diseases on the 1q21.1 location. In case of a duplication of GJA5 tetralogy of Fallot is more common. In case of a deletion other congenital heart diseases than tetralogy of Fallot are more common.

22q11.2 deletion syndrome was estimated to affect between one in 2000 and one in 4000 live births. This estimate is based on major birth defects and may be an underestimate, because some individuals with the deletion have few symptoms and may not have been formally diagnosed. It is one of the most common causes of mental retardation due to a genetic deletion syndrome.

The prevalence of 22q11.2DS has been expected to rise because of multiple reasons: (1) Thanks to surgical and medical advances, an increasing number of people are surviving heart defects associated with the syndrome. These individuals are in turn having children. The chances of a 22q11.2DS patient having an affected child is 50% for each pregnancy; (2) Parents who have affected children, but who were unaware of their own genetic conditions, are now being diagnosed as genetic testing become available; (3) Molecular genetics techniques such as FISH (fluorescence in situ hybridization) have limitations and have not been able to detect all 22q11.2 deletions. Newer technologies have been able to detect these atypical deletions.

Recently, the syndrome has been estimated to affect up to one in 2000 live births. Testing for 22q11.2DS in over 9500 pregnancies revealed a prevalence rate of 1/992.

1q21.1 deletion syndrome or 1q21.1 (recurrent) microdeletion is a rare aberration of chromosome 1.

A human cell has one pair of identical chromosomes on chromosome 1. With the 1q21.1 deletion syndrome, one chromosome of the pair is not complete, because a part of the sequence of the chromosome is missing. One chromosome has the normal length and the other is too short.

In 1q21.1, the '1' stands for chromosome 1, the 'q' stands for the long arm of the chromosome and '21.1' stands for the part of the long arm in which the deletion is situated.

The syndrome is a form of the 1q21.1 copy number variations and it is a deletion in the distal area of the 1q21.1 part. The CNV leads to a very variable phenotype and the manifestations in individuals are quite variable. Some people who have the syndrome can function in a normal way, while others have symptoms of mental retardation and various physical anomalies.

1q21.1 microdeletion is a very rare chromosomal condition. Only 46 individuals with this deletion have been reported in medical literature as of August 2011.

Currently, research is focusing on identifying the role of the genes on 18p in causing the signs and symptoms associated with deletions of 18p. This will ultimately enable predictive genotyping.

TGIF-Mutations and deletions of this gene 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.

A 'de novo'-situation appears in about 75% of the cases. In 25% of the cases, one of the parents is carrier of the syndrome, without any effect on the parent. Sometimes adults have mild problems with the syndrome. To find out whether either of the parents carries the syndrome, both parents have to be tested. In several cases, the syndrome was identified with the child, because of an autism disorder or another problem, and later it appeared that the parent was affected as well. The parent never knew about it up till the moment that the DNA-test proved the parent to be a carrier.

In families where both parents have been tested negative on the syndrome, chances on a second child with the syndrome are extremely low. If the syndrome was found in the family, chances on a second child with the syndrome are 50%, because the syndrome is autosomal dominant. The effect of the syndrome on the child cannot be predicted.

The syndrome can be detected with fluorescence in situ hybridization and Affymetrix GeneChip Operating Software.

For parents with a child with the syndrome, it is advisable to consult a physician before a next pregnancy and to do prenatal screening.

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.

A contiguous gene syndrome (CGS), also known as a contiguous gene deletion syndrome is a clinical phenotype caused by a chromosomal abnormality, such as a deletion or duplication that removes several genes lying in close proximity to one another on the chromosome. The combined phenotype of the patient is a combination of what is seen when any individual has disease-causing mutations in any of the individual genes involved in the deletion. While it can be caused by deleted material on a chromosome, it is not, strictly speaking, the same entity as a segmental aneuploidy syndrome. A segmental aneuploidy syndrome is a subtype of CGS that regularly recur, usually due to non-allelic homologous recombination between low copy repeats in the region. Most CGS involve the X chromosome and affect male individuals.

One of the earliest and most famous examples of a CGS involves a male patient with Duchenne muscular dystrophy (DMD), chronic granulomatous disease (CGD), retinitis pigmentosa and intellectual disability. When it was discovered that an X chromosome deletion (specifically Xp21) was the underlying cause of all of these features, researchers were able to use this information to clone the genes responsible for DMD and CGD.

One of those more common CGS involves a deletion on the X chromosome (near Xp21) that encompasses "DMD" (causing Duchenne muscular dystrophy), "NROB1" (causing X-linked adrenal hypoplasia congenita) and "GK" (causing glycerol kinase deficiency). These patients will have all the common features of each individual disease, resulting in a very complex phenotype. Deletions near the distal tip of the p arm of the X chromosome are also a frequent cause of CGS. In addition to the previously described CGS that occur on the X chromosome, two other common syndromes are Langer-Giedion syndrome (caused by deletions of "TRPS1" and "EXT1" on 8q24 and WAGR syndrome (caused by deletions on 11q13 encompassing "PAX6" and "WT1".)

Opitz G/BBB Syndrome is a rare genetic condition caused by one of two major types of mutations: MID1 mutation on the short (p) arm of the X chromosome or a mutation of the 22q11.2 gene on the 22nd chromosome. Since it is a genetic disease, it is an inherited condition. However, there is an extremely wide variability in how the disease presents itself.

In terms of prevention, several researchers strongly suggest prenatal testing for at-risk pregnancies if a MID1 mutation has been identified in a family member. Doctors can perform a fetal sex test through chromosome analysis and then screen the DNA for any mutations causing the disease. Knowing that a child may be born with Opitz G/BBB syndrome could help physicians prepare for the child’s needs and the family prepare emotionally. Furthermore, genetic counseling for young adults that are affected, are carriers or are at risk of carrying is strongly suggested, as well (Meroni, Opitz G/BBB syndrome, 2012). Current research suggests that the cause is genetic and no known environmental risk factors have been documented. The only education for prevention suggested is genetic testing for at-risk young adults when a mutation is found or suspected in a family member.

The minimal deletion causing this syndrome has been defined as a 3 megabase region that contains the genes GPR35, GPC1 and STK25.

Almost all deletions are found to be terminal deletions at the end of chromosome 2. There is a high frequency of "de novo" deletions, but multiple cases within a single family are also observed. Equal proportions of maternally and paternally derived rearrangements were seen in Aldred's series. No common breakpoints for the deletion were identified indicating that the 2q37 rearrangement is unlikely to be mediated by non-homologous recombination and low-copy repeats. In a study of 20 patients, no clear relationship was found between clinical features and the size or position of the monosomic region.

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The Chromosome 18 Registry & Research Society in Europe

Chromosome 18 Clinical Research Center, University of Texas Health Science Center at San Antonio

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2q37 monosomy is a rare genetic disorder caused by a deletion of a segment at the end of chromosome 2.

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).

22q11.2 duplication syndrome is a rare genetic disorder caused by a duplication of a segment at the end of chromosome 22.

The majority of 22q11 duplications are inherited often from a parent with a normal or near-normal phenotype. This is in sharp distinction to 22q11 deletion syndrome where about 90% of cases are caused by mutations that occur "de novo".

17q21.31 microdeletion syndrome (Koolen De Vries syndrome) is a rare genetic disorder caused by a deletion of a segment of chromosome 17 which contains six genes. This deletion syndrome was discovered independently in 2006 by three different research groups.

8p23.1 duplication syndrome is a rare genetic disorder caused by a duplication of a region from human chromosome 8. This duplication syndrome has an estimated prevalence of 1 in 64,000 births and is the reciprocal of the 8p23.1 deletion syndrome. The 8p23.1 duplication is associated with a variable phenotype including one or more of speech delay, developmental delay, mild dysmorphism, with prominent forehead and arched eyebrows, and congenital heart disease (CHD).

Wolf–Hirschhorn syndrome (WHS), also known as chromosome deletion Dillan 4p syndrome, Pitt–Rogers–Danks syndrome (PRDS) or Pitt syndrome, was first described in 1961 by Americans Herbert L. Cooper and Kurt Hirschhorn and, thereafter, gained worldwide attention by publications by the German Ulrich Wolf, and Hirschhorn and their co-workers, specifically their articles in the German scientific magazine "Humangenetik". It is a characteristic phenotype resulting from a partial deletion of chromosomal material of the short arm of chromosome 4 (del(4p16.3)).