The features associated with this condition include: mild to moderate learning difficulties, short stature, unique facial features, small head and skeletal abnormalities including bony growths projecting from the surfaces of bones. Typically individuals with Langer–Giedion syndrome have fine scalp hair, ears that may be large or prominent, broad eyebrows, deep-set eyes, a bulbous nose, long narrow upper lip, and missing teeth.

The most common characteristics include a distinct craniofacial phenotype (microcephaly, micrognathia, short philtrum, prominent glabella, ocular hypertelorism, dysplastic ears and periauricular tags), growth restriction, intellectual disability, muscle hypotonia, seizures, and congenital heart defects. Less common characteristics include hypospadias, colobomata of the iris, renal anomalies, and deafness. Antibody deficiencies are also common, including common variable immunodeficiency and IgA deficiency. T-cell immunity is normal.

Potocki–Shaffer syndrome (PSS), also known as DEFECT11 syndrome or chromosome 11p11.2 deletion syndrome, is a rare contiguous gene syndrome that results from the microdeletion of section 11.2 on the short arm of chromosome 11 (11p11.2). The syndrome has its name from Dr. Lorraine (Lori) Potocki and Dr. Lisa Shaffer who discovered the deletion on the 11th chromosome and studied the impacts.

The deletion of this combination of genes results in several distinctive congenital features, occasional defects in the heart, kidneys, and urinary tract. The disorder is associated with an enlarged parietal foramina which can cause openings in the two bones that form the top and sides of the skull. These abnormal openings form extra "soft spots" on the head, in addition to the two that newborns normally have, and unlike the usual newborn soft spots, the enlarged parietal foramina remain open throughout life. Other signs can include multiple mostly noncancerous benign bone tumours called osteochondromas (exostosis), developmental delay, vision disorders and craniofacial abnormalities. It is classified as a rare disease.

The signs and symptoms of Potocki–Shaffer syndrome vary widely. In addition to multiple osteochondromas and enlarged parietal foramina, affected individuals often have intellectual disability and delayed development of speech, motor skills (such as sitting and walking), and social skills. Many people with this condition have distinctive facial features, which can include a wide, short skull (brachycephaly); a prominent forehead; a narrow bridge of the nose; a shortened distance between the nose and upper lip (a short philtrum); and a downturned mouth. Less commonly, Potocki–Shaffer syndrome causes vision problems, additional skeletal abnormalities, and defects in the heart, kidneys, and urinary tract.

Langer–Giedion syndrome (LGS) is a very uncommon autosomal dominant genetic disorder caused by a deletion of chromosomal material. It is named after the two doctors who undertook the main research into the condition in the 1960s. Diagnosis is usually made at birth or in early childhood.

Affected individuals present with a broad array of medical and behavioral manifestations (tables 1 and 2). Patients are consistently characterized by global developmental delay, intellectual disability, speech abnormalities, ASD-like behaviors, hypotonia and mild dysmorphic features. Table 1 summarizes the dysmorphic and medical conditions that have been reported in individuals with PMS. Table 2 summarize the psychiatric and neurological associated with PMS. Most of the studies include small samples or relied on parental report or medical record review to collect information, which can account in part for the variability in the presentation of some of the presenting features. Larger prospective studies are needed to further characterize the phenotype.

Table 1: Dysmorphic features and medical comorbid conditions that have been reported in individuals with Phelan McDermid Syndrome.

Table 2: Psychiatric and Neurologic Manifestations associated with Phelan McDermid Syndrome

Almost all patients with this syndrome have some degree of mental retardation and facial dysmorphism (round face, deep-set eyes, thin upper lip). Behavioural problems are common. Brachymetaphalangism (metacarpal or metatarsal shortening) is reported in ~50% of cases overall, but is typically not evident below the age of 2 years. There is striking phenotypic variability, and the size and extent of the deleted region cannot be used as accurate predictors of prognosis. Some patients have additional problems such as congenital heart disease and seizures.

The brain is abnormally smooth, with fewer folds and grooves. The face, especially in children, has distinct characteristics including a short nose with upturned nares, thickened upper lip with a thin vermilion upper border, frontal bossing, small jaw, low-set posteriorily rotated ears, sunken appearance in the middle of the face, widely spaced eyes, and hypertelorism. The forehead is prominent with bitemporal hollowing.

Characteristics that are not visual include mental retardation, pre- and postnatal growth retardation, epilepsy, and reduced lifespan.

Failure to thrive, feeding difficulties, seizures and decreased spontaneous activity are often seen. Death usually occurs in infancy and childhood.

Multiple abnormalities of the brain, kidneys, and gastrointestinal tract (the stomach and intestines) may occur.

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".)

The symptoms associated with this syndrome are variable, but common features include: low birthweight, low muscle tone at birth, poor feeding in infancy (often requiring feeding by tube for a period) and oromotor dyspraxia together with moderate developmental delays and learning disabilities but amiable behaviour. Other clinically important features include epilepsy, heart defects (atrial septal defect, ventricular septal defect) and kidney/urological anomalies. Silvery depigmentation of strands of hair have been noted in several patients. With age there is an apparent coarsening of facial features. 17q21.3 was reported simultaneously in 2006 by three independent groups, with each group reporting several patients, and is now recognised to be one of the more common recurrent microdeletion syndromes. Recently a patient with a small duplication in same segment of DNA has been described. An overview of the clinical features of the syndrome, by reviewing 22 individuals with a 17q21.31 microdeletion, estimated the disorder is present in one in every 16,000 people.

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)).

The clinical phenotype of 3q29 microdeletion syndrome is variable. Clinical features can include mild/moderate mental retardation with mildly dysmorphic facial features (long and narrow face, short philtrum and a high nasal bridge). Of the 6 reported patients, additional features including autism, ataxia, chest-wall deformity and long, tapering fingers were found in at least two patients. A review of 14 children with insterstitial deletions of 3q29, found 11 who had the common recurrent 1.6Mb deletion and displayed mental retardation and microcephaly.

The variability of phenotype is underscored by the report on a 6 and 9/12 year-old male patient with a de novo chromosome 3q29 microdeletion identified by BAC array comparative genomic hybridization assay (aCGH), with accompanying normal 46,XY high-resolution chromosome analysis. The patient has language-based learning disabilities and behavioral features consistent with diagnoses of autism and attention deficit hyperactivity disorder (ADHD) of the inattentive type. He also displays some other features previously associated with chromosome 3q29 microdeletion such as an elongated face, long fingers, and joint laxity. Most notably the patient, per formal IQ testing, was not found to have frank mental retardation as has been previously reported among patients with chromosome 3q29 terminal deletion, but rather the patient has demonstrated an average full-scale IQ result. This report further expands the phenotypic spectrum to include the possibility of normal intelligence as corroborated by formal, longitudinal psycho-educational testing.

The presence of two homologous low copy repeats either side of the deletion break-point suggests that non-allelic homologous recombination is the likely mechanism underlying this syndrome.

The syndrome gets its name from the characteristic cry of affected infants, which is similar to that of a meowing kitten, due to problems with the larynx and nervous system. About 1/3 of children lose the cry by age of 2 years. Other symptoms of cri du chat syndrome may include:

- feeding problems because of difficulty in swallowing and sucking;

- low birth weight and poor growth;

- severe cognitive, speech, and motor delays;

- behavioral problems such as hyperactivity, aggression, outbursts, and repetitive movements;

- unusual facial features which may change over time;

- excessive drooling;

- small head and jaw;

- wide eyes;

- skin tags in front of eyes.

Other common findings include hypotonia, microcephaly, growth retardation, a round face with full cheeks, hypertelorism, epicanthal folds, down-slanting palpebral fissures, strabismus, flat nasal bridge, down-turned mouth, micrognathia, low-set ears, short fingers, single palmar creases, and cardiac defects (e.g., ventricular septal defect [VSD], atrial septal defect [ASD], patent ductus arteriosus [PDA], tetralogy of Fallot). Infertility is not associated with Cri du chat.

It has also been observed that people with the condition have difficulties communicating. While levels of proficiency can range from a few words to short sentences, it is often recommended by medical professionals for the child to undergo some sort of speech therapy/aid with the help of a professional.

Less frequently encountered findings include cleft lip and palate, preauricular tags and fistulas, thymic dysplasia, intestinal malrotation, megacolon, inguinal hernia, dislocated hips, cryptorchidism, hypospadias, rare renal malformations (e.g., horseshoe kidneys, renal ectopia or agenesis, hydronephrosis), clinodactyly of the fifth fingers, talipes equinovarus, pes planus, syndactyly of the second and third fingers and toes, oligosyndactyly, and hyperextensible joints. The syndrome may also include various dermatoglyphics, including transverse flexion creases, distal axial triradius, increased whorls and arches on digits, and a single palmar crease.

Late childhood and adolescence findings include significant intellectual disability, microcephaly, coarsening of facial features, prominent supraorbital ridges, deep-set eyes, hypoplastic nasal bridge, severe malocclusion, and scoliosis.

Affected females reach puberty, develop secondary sex characteristics, and menstruate at the usual time. The genital tract is usually normal in females except for a report of a bicornuate uterus. In males, testes are often small, but spermatogenesis is thought to be normal.

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).

Recognised symptoms are:

- Only one set of genes on the two chromosomes function (Haploinsufficiency)

- Thrombocytopenia-absent radius (TAR syndrome), in case of a class II-deletion

- Neurological-psychiatric problems: Autism; schizophrenia; epilepsy; learning problems; cognitive disabilities — mild to moderate; developmental delay — mild to moderate (milestones like sitting, standing and walking; come at a later period in childhood); children show an ataxic gait and fall down a lot

- Dysmorphism: Slightly unusual facial appearance; disturbed growth; skeletal malformations; small head (microcephaly); prominent forehead; bulbous nose; deep-set eyes; broad thumbs; broad toes; squint; very flexible joints; clavicular pseudoarthrosis (the collarbone doesn't develop normally) (Class II-deletion); An extra transverse crease of the fifth finger (Class II-deletion)); Problems with the development of the vagina (Müllerian aplasia)

- Eyes: Cataracts

- Heart abnormalities and cardiovascular anomalies (30% of the cases): Anomalous origin of the coronary artery (Class II-deletion)

- Kidneys: Missing kidney or floating kidneys

- Cancer: Neuroblastoma

- Sleep disturbances

It is not clear whether the list of symptoms is complete. Very little information is known about the syndrome. The syndrome can have completely different effects on members of the same family.

A common deletion is between 1.0–1.9Mb. Mefford states that the standard for a deletion is 1.35Mb. The largest deletion seen on a living human is over 5 Mb.

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

The three most common symptoms of Opitz G/BBB syndrome (both type I & II) are hypertelorism (exceptionally wide-spaced eyes), laryngo-tracheo-esophalgeal defects (including clefts and holes in the palate, larynx, trachea and esophagus) and hypospadias (urinary openings in males not at the tip of the penis) (Meroni, Opitz G/BBB syndrome, 2012). Abnormalities in the larynx, trachea and esophagus can cause significant difficulty breathing and/or swallowing and can result in reoccurring pneumonia and life-threatening situations. Commonly, there may be a gap between the trachea and esophagus, referred to as a laryngeal cleft; which can allow food or fluid to enter the airway and make breathing and eating a difficult task.

Genital abnormalities like a urinary opening under the penis (hypospadias), undescended testes (cryptorchidism), underdeveloped scrotum and a scrotum divided into two lobes (bifid scrotum) can all be commonplace for males with the disease.

Developmental delays of the brain and nervous system are also common in both types I and II of the disease. 50% of people with Opitz G/BBB Syndrome will experience developmental delay and mild intellectual disability. This can impact motor skills, speech and learning capabilities. Some of these instances are likened to autistic spectrum disorders. Close to half of the people with Opitz G/BBB Syndrome also have a cleft lip (hole in the lip opening) and possibly a cleft palate (hole in the roof of the mouth), as well. Less than half of the people diagnosed have heart defects, imperforate anus (obstructed anal opening), and brain defects. Of all the impairments, female carriers of X-linked Type I Opitz G/BBB Syndrome usually only have ocular hypertelorism.

Recognised symptoms up till now are:

- Autism or autistic behaviors

- ADHD

- Learning disability

- Large head

- Dysmorphic facial appearance - mild

- Prominent forehead

- Wide-set eyes (hypertelorism)

- Schizophrenia

- Loose joints

- GERD

- Sleep disturbances

- Sleep Apnea

- Underdeveloped parts of brain - corpus callosum and cerebellar vermis

- Neuroblastoma

- Speech & developmental delays

- Chiari malformation of the brain

- Congenital heart defects

- Hypotonia

It is not clear whether the list of symptoms is complete. Very little information is known about the syndrome. The symptomology may be different among individuals, even in the same family.

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).

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.

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.

Recurrent seizures are the most recognizable feature of this syndrome and are most often the first sign of this syndrome. These syndromes are often ongoing and poorly responsive to anti-seizure medications. Most patients develop seizures the first few years of life, but the age of onset ranges from ages 1 to 17. Different types of seizure have been reported in this syndrome. The most common seizure type appears to be brief focal onset epileptic seizures with impairment of consciousness and awareness, known as complex partial seizures. Other features you may see in these complex partial seizures include staring, oral automatisms, unspecified automatic behavior, involuntary motor movements and/or head turning.

Furthermore, many patients have subtle nighttime behavioral changes, such as stretching, rubbing, and turning resembling a nighttime awakening. However, electroencephalography (EEG) studies during these events show abnormal electrical seizure activity, indicating that nocturnal behavioral events are actually subtle nocturnal seizures or non-convulsive status epilepticus. Many of these patients experience their seizures only during sleep. They can have seemingly bizarre features as they originate from the frontal lobe of the brain. Often, individuals with ring chromosome 20 syndrome are initially found to have complex partial seizures of frontal lobe origin, though imaging studies do not show a corresponding structural brain abnormality. In certain patients, these seizures may secondarily generalized.

Individuals from the ages of 0–17 years should be considered for ring 20 chromosome analysis if they have: predominantly complex partial seizures, medically refractory cryptogenic epilepsy, Lennox-Gastaut-like features with no cause identified, frequent subtle nocturnal seizures, an EEG showing prolonged high voltage frontally dominant slowing intermixed with spikes or sharp waves, an EEG showing overlapping features of continuous slow spike and wave discharges in sleep (CSWS) and electrical status epilepticus in sleep (ESES), and/or subsequent cognitive impairment/learning difficulties/mild retardation.These patients will typically have a normal childhood development until onset of epilepsy and lack evidence of dysmorphism or other congenital malformations.

This autosomal dominant disorder is characterized by a number of health defects including Hirschsprung's disease, intellectual disability, epilepsy, delayed growth and motor development, congenital heart disease, genitourinary anomalies and absence of the corpus callosum. However, Hirschsprung's disease is not present in all infants with Mowat–Wilson syndrome and therefore it is not a required diagnostic criterion. Distinctive physical features include microcephaly, narrow chin, cupped ears with uplifted lobes with central depression, deep and widely set eyes, open mouth, wide nasal bridge and a shortened philtrum.

3q29 microdeletion syndrome is a rare genetic disorder resulting from the deletion of a segment of chromosome 3. This syndrome was first described in 2005.

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.

The phenotypic data on 11 patients indicated that cases are not always ascertained for CHD but that CHD was the most common single feature found in 6 out of 11 individuals. Developmental delay and/or learning difficulties were found in 5 out of 11 cases, but one prenatal case was developing normally at 15 months of age (Case 1,). Three other prenatal cases could not yet be reliably assessed. A variable degree of facial dysmorphism was present in 5 out of 11 individuals. Partial toe syndactyly has been found in one mother and son diad and adrenal anomalies in two probands but not in the duplicated mother of one of them. The phenotype is compatible with independent adult life with varying degrees of support.

Duplication of the GATA4 transcription factor () is believed to underlie the congenital heart disease and other genes, common to the duplication and deletion syndromes, can be regarded as candidates for the 8p23.1 duplication syndrome. These include the SOX7 transcription factor () for both CHD and developmental delay and the TNKS gene () for behavioural difficulties. The diaphragmatic hernia found in the 8p23.1 deletion syndrome has not been found in the 8p23.1 duplication syndrome to date.

The duplication may be associated with copy number changes of the adjacent olfactory receptor/defensin repeats (ORDRs) that predispose to the 8p23.1 deletion and duplication syndromes. High total copy numbers of these repeats have been associated with predisposition to psoriasis and low copy number with predisposition to Crohn's disease.