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.

Exposure of spermatozoa to lifestyle, environmental and/or occupational hazards may increase the risk of aneuploidy. Cigarette smoke is a known aneugen (aneuploidy inducing agent). It is associated with increases in aneuploidy ranging from 1.5 to 3.0-fold. Other studies indicate factors such as alcohol consumption, occupational exposure to benzene, and exposure to the insecticides fenvalerate and carbaryl also increase aneuploidy.

About half of all 'marker' chromosomes are idic(15) but idic(15) in itself is one of the rare chromosome abnormalities. Incidence at birth appears to be 1 in 30,000 with a sex ratio of almost 1:1; however, since dysmorphic features are absent or subtle and major malformations are rare, chromosome analysis may not be thought to be indicated, and some individuals, particularly in the older age groups, probably remain undiagnosed. There are organizations for families with idic(15) children that offer extensive information and support.

Since tetrasomy 9p is not usually inherited, the risk of a couple having a second child with the disorder is minimal. While patients often do not survive to reproductive age, those who do may or may not be fertile. The risk of a patient's child inheriting the disorder is largely dependent on the details of the individual's case.

Human trisomies compatible with live birth, other than Down syndrome (trisomy 21), are Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13). Complete trisomies of other chromosomes are usually not viable and represent a relatively frequent cause of miscarriage. Only in rare cases of a mosaicism, the presence of a normal cell line, in addition to the trisomic cell line, may support the development of a viable trisomy of the other chromosomes.

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.

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

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.

Microdeletions in the Y chromosome have been found at a much higher rate in infertile men than in fertile controls and the correlation found may still go up as improved genetic testing techniques for the Y chromosome are developed.

Much study has been focused upon the "azoospermia factor locus" (AZF), at Yq11. A specific partial deletion of AZFc called "gr/gr deletion" is significantly associated with male infertility among Caucasians in Europe and the Western Pacific region.

Additional genes associated with spermatogenesis in men and reduced fertility upon Y chromosome deletions include RBM, DAZ, SPGY, and TSPY.

Though the outcome for individuals with either form of the tetrasomy is highly variable, mosaic individuals consistently experience a more favourable outcome than those with the non-mosaic form. Some affected infants die shortly after birth, particularly those with the non-mosaic tetrasomy. Many patients do not survive to reproductive age, while others are able to function relatively normally in a school or workplace setting. Early diagnosis and intervention has been shown to have a strong positive influence on the prognosis.

Diploid-triploid mosaicism (DTM) is a chromosome disorder. Individuals with diploid-triploid syndrome have some cells with three copies of each chromosome for a total of 69 chromosomes (called triploid cells) and some cells with the usual 2 copies of each chromosome for a total of 46 chromosomes (called diploid cells).

Having two or more different cell types is called mosaicism. Diploid-triploid mosaicism can be associated with truncal obesity, body/facial asymmetry, weak muscle tone (hypotonia), delays in growth, mild differences in facial features, fusion or webbing between some of the fingers and/or toes (syndactyly) and irregularities in the skin pigmentation.

Intellectual disabilities may be present but are highly variable from person to person ranging from mild to more severe.

The chromosome disorder is usually not present in the blood; a skin biopsy, or analyzing cells in the urine is needed to detect the triploid cells.

A regular human carries 23 pairs of chromosomes in his or her cells. Cells containing two pairs of chromosomes are known as diploid cells. Those with diploid triploid mosaicism have some cells which are triploid, meaning that they have three copies of chromosomes, or a total of 69 chromosomes. Triploidy is distinct from trisomy, in which only one chromosome exists in three pairs. A well-known example of trisomy is trisomy 21 or Down 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".)

More than 80% of children with Patau syndrome die within the first year of life. Children with the mosaic variation are usually affected to a lesser extent. In a retrospective Canadian study of 174 children with trisomy 13, median survival time was 12.5 days. One and ten year survival was 19.8% and 12.9% respectively.

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.

At the present time, there is no specific treatment that can undo any chromosomal abnormality, nor the genetic pattern seen in people with idic(15). The extra chromosomal material in those affected was present at or shortly after conception, and its effects on brain development began taking place long before the child was born. Therapies are available to help address many of the symptoms associated with idic(15). Physical, occupational, and speech therapies along with special education techniques can stimulate children with idic(15) to develop to their full potential.

In terms of medical management of the symptoms associated with Chromosome 15q11.2-q13.1 Duplication Syndrome, families should be aware that individuals with chromosome 15 duplications may tolerate medications differently and may be more sensitive to side effects for some classes of medications, such as the serotonin reuptake inhibitor type medications (SSRI).

Thus, these should be used with caution and any new medication should be instituted in a controlled setting, with slow titration of levels and with a clear endpoint as to what the expected outcome for treatment is.

There is an increased risk of sudden, unexpected death among children and adults with this syndrome. The full cause is not yet understood but it is generally attributed to SUDEP (Sudden Unexplained Death in Epilepsy).

The mechanism of mutation is not different for Y-chromosome microdeletion. However, the ability to repair it differs from other chromosomes. The human Y chromosome is passed directly from father to son, and is not protected against accumulating copying errors, whereas other chromosomes are error corrected by recombining genetic information from mother and father. This may leave natural selection as the primary repair mechanism for the Y chromosome.

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.

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).

The incidence rate of ATR-16 syndrome is not easy to estimate and it is thought to be underdiagnosed. Scientists have described more than 20 cases as of 2013.

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.

Males with pathogenic "MECP2" mutations usually die within the first 2 years from severe encephalopathy, unless they have an extra X chromosome (often described as Klinefelter syndrome), or have somatic mosaicism.

Male fetuses with the disorder rarely survive to term. Because the disease-causing gene is located on the X chromosome, a female born with an MECP2 mutation on her X chromosome has another X chromosome with an ostensibly normal copy of the same gene, while a male with the mutation on his X chromosome has no other X chromosome, only a Y chromosome; thus, he has no normal gene. Without a normal gene to provide normal proteins in addition to the abnormal proteins caused by a MECP2 mutation, the XY karyotype male fetus is unable to slow the development of the disease, hence the failure of many male fetuses with a MECP2 mutation to survive to term.

Females with a MECP2 mutation, however, have a non-mutant chromosome that provides them enough normal protein to survive longer. Research shows that males with Rett syndrome may result from Klinefelter's syndrome, in which the male has an XXY karyotype. Thus, a non-mutant "MECP2" gene is necessary for a Rett's-affected embryo to survive in most cases, and the embryo, male or female, must have another X chromosome.

There have, however, been several cases of 46,XY karyotype males with a MECP2 mutation (associated with classical Rett syndrome in females) carried to term, who were affected by neonatal encephalopathy and died before 2 years of age. The incidence of Rett syndrome in males is unknown, partly owing to the low survival of male fetuses with the Rett syndrome-associated MECP2 mutations, and partly to differences between signs caused by MECP2 mutations and those caused by Rett's.

Females can live up to 40 years or more. Laboratory studies on Rett syndrome may show abnormalities such as:

- EEG abnormalities from 2 years of age

- atypical brain glycolipids

- elevated CSF levels of "beta"-endorphin and glutamate

- reduction of substance P

- decreased levels of CSF nerve growth factors

A high proportion of deaths are abrupt, but most have no identifiable cause; in some instances death is the result most likely of:

- spontaneous brainstem dysfunction

- cardiac arrest, likely due to long QT syndrome, ventricular tachycardia or other arrhythmias

- seizures

- gastric perforation

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:

Edwards syndrome occurs in about one in 5,000 live births, but more conceptions are affected by the syndrome because the majority of those diagnosed with the condition prenatally will not survive to birth. Although women in their 20s and early 30s may conceive babies with Edwards syndrome, the risk of conceiving a child with it increases with a woman's age. The average maternal age for conceiving a child with this disorder is 32½.

Patau syndrome is the result of trisomy 13, meaning each cell in the body has three copies of chromosome 13 instead of the usual two. A small percentage of cases occur when only some of the body's cells have an extra copy; such cases are called mosaic Patau.

Patau syndrome can also occur when part of chromosome 13 becomes attached to another chromosome (translocated) before or at conception in a Robertsonian translocation. Affected people have two copies of chromosome 13, plus extra material from chromosome 13 attached to another chromosome. With a translocation, the person has a partial trisomy for chromosome 13 and often the physical signs of the syndrome differ from the typical Patau syndrome.

Most cases of Patau syndrome are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). An error in cell division called non-disjunction can result in reproductive cells with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of the chromosome. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 13 in each of the body's cells. Mosaic Patau syndrome is also not inherited. It occurs as a random error during cell division early in fetal development.

Patau syndrome due to a translocation can be inherited. An unaffected person can carry a rearrangement of genetic material between chromosome 13 and another chromosome. This rearrangement is called a balanced translocation because there is no extra material from chromosome 13. Although they do not have signs of Patau syndrome, people who carry this type of balanced translocation are at an increased risk of having children with the condition.