A contiguous gene syndrome (CGS), also known as a contiguous gene deletion syndrome, is a clinical

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...

caused by a

chromosomal A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

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 Non-allelic homologous recombination (NAHR) is a form of homologous recombination that occurs between two lengths of DNA that have high sequence similarity, but are not alleles. It usually occurs between sequences of DNA that have been previously ...

between low copy repeats in the region. Most CGS involve the

X chromosome The X chromosome is one of the two sex-determining chromosomes ( allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO se ...

and affect male individuals. One of the earliest and most famous examples of a CGS involves a male patient with

Duchenne muscular dystrophy Duchenne muscular dystrophy (DMD) is a severe type of muscular dystrophy that primarily affects boys. Muscle weakness usually begins around the age of four, and worsens quickly. Muscle loss typically occurs first in the thighs and pelvis follo ...

(DMD),

chronic granulomatous disease Chronic granulomatous disease (CGD), also known as Bridges–Good syndrome, chronic granulomatous disorder, and Quie syndrome, is a diverse group of hereditary diseases in which certain cells of the immune system have difficulty forming the reacti ...

(CGD),

retinitis pigmentosa Retinitis pigmentosa (RP) is a genetic disorder of the eyes that causes loss of vision. Symptoms include trouble seeing at night and decreasing peripheral vision (side and upper or lower visual field). As peripheral vision worsens, people may ...

and

intellectual disability Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation, Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signif ...

. 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 Clone or Clones or Cloning or Cloned or The Clone may refer to: Places * Clones, County Fermanagh * Clones, County Monaghan, a town in Ireland Biology * Clone (B-cell), a lymphocyte clone, the massive presence of which may indicate a pathologi ...

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 DMD may refer to: Science and medicine * Dimethyldioxirane, an organic molecule * Doctor of Dental Medicine, an academic degree for the profession of Dentistry * Duchenne muscular dystrophy, a neurodegenerative disease * Dysmyelogenic leukod ...

'' (causing Duchenne muscular dystrophy), ''

NROB1 DAX1 (dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1) is a nuclear receptor protein that in humans is encoded by the ''NR0B1'' gene (nuclear receptor subfamily 0, group B, member 1). The ''NR0B1'' gene i ...

'' (causing

X-linked adrenal hypoplasia congenita X-linked adrenal hypoplasia congenita is a genetic disorder that mainly affects males. It involves many endocrine tissues in the body, especially the adrenal glands. Presentation One of the main characteristics of this disorder is adrenal insuff ...

) 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 Langer–Giedion syndrome (LGS) is a very uncommon autosomal dominant genetic disorder caused by a deletion of a small section of material on chromosome 8. It is named after the two doctors who undertook the main research into the condition in the ...

(caused by deletions of ''

TRPS1 Zinc finger transcription factor Trps1 is a protein that in humans is encoded by the ''TRPS1'' gene. This gene encodes a GATA-like transcription factor that represses GATA-regulated genes and binds to a dynein Dyneins are a family of cytoskel ...

'' and '' EXT1'' on 8q24 and

WAGR syndrome WAGR syndrome (also known as WAGR complex, Wilms tumour-aniridia syndrome, aniridia-Wilms tumour syndrome) is a rare genetic syndrome in which affected children are predisposed to develop Wilms tumour (a tumour of the kidneys), Aniridia (absence ...

(caused by deletions on 11q13 encompassing ''

PAX6 Paired box protein Pax-6, also known as aniridia type II protein (AN2) or oculorhombin, is a protein that in humans is encoded by the ''PAX6'' gene. Function PAX6 is a member of the Pax gene family which is responsible for carrying the genet ...

'' and '' WT1''.)

References

{{reflist Genetic syndromes Chromosomal abnormalities