Bloom syndrome is characterized by genome instability. The most prominent features include short stature and a rash on the face that develops early in life when exposed to the sun. The skin rash is erythematous, telangiectatic, infiltrated, and scaly, it can appear across the nose, on the cheeks and around the lips. As well as these areas the rash will develop on any other sun-exposed areas including, the backs of the hands and neck. Other clinical features include a high-pitched voice; distinct facial features, including a long, narrow face, micrognathism, and prominent nose and ears; pigmentation changes of the skin including hypo-pigmented and hyper-pigmented areas, cafe-au-lait spots, and telangiectasias (dilated blood vessels), which can appear on the skin and eyes. Moderate immune deficiency, characterized by deficiency in certain immunoglobulin classes has also been related to BS, leading to recurrent pneumonia and ear infections. Most individuals with Bloom syndrome are born with a low birth weight. Hypogonadism is characterized by a failure to produce sperm, hence infertility in males, and premature cessation of menses (premature menopause), hence sub-fertility in females. However, several women with Bloom syndrome have had children. The most serious and common complication of Bloom syndrome is cancer. Other complications of the disorder include chronic obstructive lung disease, diabetes, and learning disabilities. There is no evidence that mental retardation is more common in Bloom syndrome than in other people. People with Bloom Syndrome have a shortened life expectancy; the average life span is approximately 27 years. Bloom syndrome shares some features with Fanconi anemia possibly because there is overlap in the function of the proteins mutated in this related disorder.

Chromosome instability syndromes are a group of inherited conditions associated with chromosomal instability and breakage. They often lead to an increased tendency to develop certain types of malignancies.

The following chromosome instability syndromes are known:

- Ataxia telangiectasia

- Ataxia telangiectasia-like disorder

- Bloom syndrome

- Fanconi anaemia

- Nijmegen breakage syndrome

Bloom syndrome (often abbreviated as BS in literature), also known as Bloom-Torre-Machacek syndrome, is a rare autosomal recessive disorder characterized by short stature, predisposition to the development of cancer and genomic instability. BS is caused by mutations in the BLM gene leading to mutated DNA helicase protein formation. Cells from a person with Bloom syndrome exhibit a striking genomic instability that includes excessive crossovers between homologous chromosomes and sister chromatid exchanges (SCEs). The condition was discovered and first described by New York dermatologist Dr. David Bloom in 1954.

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.

ATR-16 syndrome affects the blood, development, and brain; symptoms vary based on the specific genes deleted on chromosome 16. Because it is so rare, it is difficult to determine the "core" symptoms of the disease. People with ATR-16 have alpha-thalassemia, a blood disorder where there is less normal hemoglobin in the blood than there should be, and the red blood cells are smaller than they should be (microcytic anemia). Affected children have various characteristic physical features, including clubfoot, "locked" little fingers, microcephaly (small head), hypertelorism (widely spaced eyes), broad, prominent nose bridge, downward-slanted palpebral fissures, small ears, retrognathia, and short neck. Children with ATR-16 syndrome also have mild to moderate intellectual disabilities, developmental delays/growth delays, and speech delays. Some children with ATR-16 have seizures, cryptorchidism (undescended testes), or hypospadias.

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.

ICF syndrome (or Immunodeficiency, Centromere instability and Facial anomalies syndrome) is a very rare autosomal recessive immune disorder.

It is characterized by variable reductions in serum immunoglobulin levels which cause most ICF patients to succumb to infectious diseases before adulthood. ICF syndrome patients exhibit facial anomalies which include hypertelorism, low-set ears, epicanthal folds and macroglossia.

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.

Infants with Emanuel syndrome have weak muscle tone (hypotonia) and fail to gain weight and grow at the expected rate (failure to thrive). Their development is significantly delayed, and most affected individuals have severe to profound intellectual disability. Other features of Emanuel syndrome include an unusually small head (microcephaly), distinctive facial features, and a small lower jaw (micrognathia). Ear abnormalities are common, including small holes in the skin just in front of the ears (preauricular pits or sinuses). About half of all affected infants are born with an opening in the roof of the mouth (cleft palate) or a high arched palate. Males with Emanuel syndrome often have genital abnormalities. Additional signs of this condition can include heart defects and absent or unusually small (hypoplastic) kidneys; these problems can be life-threatening in infancy or childhood.

Complete trisomy 8 causes severe effects on the developing fetus and can be a cause of miscarriage.

Complete trisomy 8 is usually an early lethal condition, whereas trisomy 8 mosaicism is less severe and individuals with a low proportion of affected cells may exhibit a comparatively mild range of physical abnormalities and developmental delay. Individuals with trisomy 8 mosaicism are more likely to survive into childhood and adulthood, and exhibit a characteristic and recognizable pattern of developmental abnormalities. Common findings include retarded psychomotor development, moderate to severe mental retardation, variable growth patterns which can result in either abnormally short or tall stature, an expressionless face, and many musculoskeletal, visceral, and eye abnormalities, as well as other anomalies. A deep plantar furrow is considered to be pathognomonic of this condition, especially when seen in combination with other associated features. The type and severity of symptoms are dependent upon the location and proportion of trisomy 8 cells compared to normal cells.

Chromosome 5q deletion syndrome (chromosome 5q monosomy, 5q- syndrome) is an acquired, hematological disorder characterized by loss of part of the long arm (q arm, band 5q33.1) of human chromosome 5 in bone marrow myelocyte cells. This chromosome abnormality is most commonly associated with the myelodysplastic syndrome.

It should not be confused with "partial trisomy 5q", though both conditions have been observed in the same family.

This should not be confused with the germ line cri du chat (5p deletion) syndrome which is a deletion of the short arm of the 5th chromosome.

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)).

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.

The most common symptoms are intellectual disability and recurrent seizures developing in infancy or early childhood. Typically the seizures are resistant to treatment with anti-epileptic drugs. Other symptoms may include:

- Microcephaly

- Lymphedema

- Facial abnormalities

- Immune deficiencies

- Abnormalities of retina

- Slow growth

- Short stature

The severity of symptoms of idic(15) vary greatly between individuals. Individuals with idic(15) usually have delays in language development and motor skills such as walking or sitting up. Other traits may include low muscle tone (hypotonia), seizures (>50%), short stature, and intellectual disability. Distinctive facial features associated with idic(15), where present, are usually very subtle but may include epicanthal folds (skin folds at the inner corners of one or both eyes), broad forehead, a flattened nasal bridge, button nose, and a high arched palate (roof of the mouth). Many individuals with idic(15) display features of autism, such as problems with communication and social interactions, obsessional interests (often with interactive mechanisms like wheels, doors or switches), unpredictable sleep cycles (and a reduced need for sleep), and repetitive and stereotyped behaviors (e.g., lining up toys, playing with a toy in the same manner over and over again, hand flapping, rocking back and forth). A high pain threshold is often observed. If speech develops, it is often echolalic but some individuals do grasp some language. With a severely affected person there may be an inability to walk or talk.

For individuals with MORM syndrome, symptoms do not appear until about one year into the child’s life span. From conception to birth, individuals with MORM syndrome appear asymptotic with no abnormal characteristics. Vision is negatively affected within the first year of life, particularly night vision. Individuals with MORM syndrome experience decreased visual acuity meaning their ability to see distinct sharp lines decreases. Vision quality continues to deteriorate until age three. Any further reduction in vision acuity is not observed until the individual is between the ages thirty to forty. Delayed sentence processing and intellectual disability is associated with individuals with MORM syndrome, primarily observed at age four. Individuals continue to develop and grow until they are five to twelve years old. During this age bracket, truncal obesity can develop. Truncal obesity is a term used to describe the build up of fat around ones trunk or torso as opposed to the persons extremities. Males enter puberty at around age twelve and develop normally except for their sex organ. The males penis will remain at the prepubescent size resulting in a micropenis. The life span of individuals with MORM syndrome is unclear as well as the fertility of these individuals.

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.

ATR-16 syndrome, also called Alpha-Thalassemia-Intellectual disability syndrome is a rare disease characterized by monosomy on part of chromosome 16.

The acronym "MASA" describes the four major symptoms - Mental retardation, Aphasia, Shuffling gait, and Adducted thumbs. Another name for this syndrome is "L1 syndrome".

The term "CRASH", for "corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraplegia, and hydrocephalus" has also been used to describe L1CAM-related disorders.

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.

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".)

Werner syndrome patients exhibit growth retardation, short stature, premature graying of hair, alopecia (hair loss), wrinkling, prematurely aged faces with beaked noses, skin atrophy (wasting away) with scleroderma-like lesions, lipodystrophy (loss of fat tissues), abnormal fat deposition leading to thin legs and arms, and severe ulcerations around the Achilles tendon and malleoli (around ankles). Other symptoms include change in voice (weak, hoarse, high-pitched), atrophy of gonads leading to reduced fertility, bilateral cataracts (clouding of lens), premature arteriosclerosis (thickening and loss of elasticity of arteries), calcinosis (calcium deposits in blood vessels), atherosclerosis (blockage of blood vessels), type 2 diabetes, osteoporosis (loss of bone mass), telangiectasia, and malignancies. The prevalence of rare cancers, such as meningiomas, are increased in individuals with Werner syndrome.

MASA syndrome, also called CRASH syndrome, Gareis-Mason syndrome, L1 syndrome, spastic paraplegia 1 is a rare X-linked recessive neurological disorder.

Nijmegen breakage syndrome (NBS), also known as Berlin breakage syndrome, ataxia telangiectasia variant 1 (AT-V1) and Seemanova syndrome, is a rare autosomal recessive congenital disorder causing chromosomal instability, probably as a result of a defect in the double Holliday junction DNA repair mechanism and/or the synthesis dependent strand annealing mechanism for repairing double strand breaks in DNA (see Homologous recombination).

NBS1 codes for a protein (nibrin) that has two major functions: (1) to stop the cell cycle in the S phase, when there are errors in the cell DNA (2) to interact with FANCD2 that can activate the BRCA1/BRCA2 pathway of DNA repair. This explains why mutations in the NBS1 gene lead to higher levels of cancer (see Fanconi anemia, Cockayne syndrome.)

The name derives from the Dutch city Nijmegen where the condition was first described.

Most people with NBS have West Slavic origins. The largest number of them live in Poland.