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Contiguous Gene Syndromes

by Nina N. Powell-Hamilton, MD, FAAP, FACMG

Contiguous gene syndromes are disorders caused by microscopic and submicroscopic deletions or duplications of contiguous genes on particular parts of chromosomes. These syndromes differ from chromosomal deletion syndromes (see Chromosomal Deletion Syndromes) in that deletion syndromes are usually visible on karyotyping because of their larger size (typically > 5 megabases), whereas the abnormalities in contiguous gene syndromes involve smaller segments (typically 1 to 3 megabases) and are detectable only with fluorescent probes (fluorescent in situ hybridization) and microarray analysis. A given gene segment can be deleted or duplicated (termed a reciprocal duplication). The clinical effects of microscopic reciprocal duplications tend to be similar but less severe than those of deletions involving the same segment.

Most clinically significant microdeletions and duplications seem to occur sporadically; however, mildly affected parents may be diagnosed when parental testing is done after a child is found to have an abnormality. Numerous syndromes have been identified, with widely varying manifestations (see Examples of Contiguous Gene Deletion Syndromes).

Examples of Contiguous Gene Deletion Syndromes

Syndrome

Chromosomal Deletion

Description

Alagille syndrome

20p.12

Cholestasis, bile duct paucity, cardiac anomalies, pulmonary artery stenosis, butterfly vertebrae, posterior embryotoxon of the eye

Angelman syndrome

Maternal chromosome at 15q11

Seizures, puppet-like ataxia, frequent laughter, hand flapping, severe intellectual disability

DiGeorge syndrome (DiGeorge anomaly, velocardiofacial syndrome, pharyngeal pouch syndrome, thymic aplasia—see DiGeorge Syndrome)

22q11.21

Hypoplasia or lack of thymus and parathyroids, cardiac anomalies, cleft palate, intellectual disability, psychiatric problems

Langer-Giedion syndrome (trichorhinophalangeal syndrome type II)

8q24.1

Exostosis, cone epiphyses, sparse hair, bulbous nose, hearing loss, intellectual disability

Miller-Dieker syndrome

17p13.3

Lissencephaly; short, upturned nose; severe growth retardation; seizures; severe intellectual disability

Paternal chromosome at 15q11

In infancy: Hypotonia, poor feeding, failure to thrive

In childhood and adolescence: Obesity, hypogonadism, small hands and feet, intellectual disability, obsessive-compulsive behaviors

Rubinstein-Taybi syndrome

16p13

Broad thumbs and large toes, prominent nose and columella, intellectual disability

Smith-Magenis syndrome

17p11.2

Brachycephaly, midfacial hypoplasia, prognathism, hoarse voice, short stature, intellectual disability

Williams syndrome

7q11.23

Aortic stenosis, intellectual disability, elfin facies, transient hypercalcemia in infants

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