Chromosome 18, Monosomy 18p
National Organization for Rare Disorders, Inc.
It is possible that the main title of the report Chromosome 18, Monosomy 18p is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.
- Short Arm 18 Deletion Syndrome
- 18p Deletion Syndrome
- 18p- Syndrome
- Del(18p) Syndrome
- Monosomy 18p Syndrome
Chromosome 18, Monosomy 18p is a rare chromosomal disorder in which all or part of the short arm (p) of chromosome 18 is deleted (monosomic). The disorder is typically characterized by short stature, variable degrees of mental retardation, speech delays, malformations of the skull and facial (craniofacial) region, and/or additional physical abnormalities. Associated craniofacial defects may vary greatly in range and severity from case to case. However, such features commonly include an unusually small head (microcephaly); a broad, flat nose; a "carp-shaped" mouth; large, protruding ears; widely spaced eyes (ocular hypertelorism); and/or other abnormalities. Rarely (i.e., in about 10 percent of cases), Monosomy 18p may be associated with holoprosencephaly, a condition in which the forebrain (prosencephalon) fails to divide properly during embryonic development. Holoprosencephaly may result in varying degrees of mental retardation, other neurologic findings, and/or extremely variable midline facial defects, such as the presence of a single, central front tooth (maxillary incisor); closely spaced eyes (hypotelorism); an abnormal groove in the upper lip (cleft lip); incomplete closure of the roof of the mouth (cleft palate); and/or, in severe cases, absence of the nose and/or cyclopia. Cyclopia is characterized by fusion of the eye cavities (orbits) into a single cavity containing one eye.
In some individuals with Monosomy 18p, additional physical abnormalities may be present. Such findings commonly include a short, webbed neck; a broad chest with widely spaced nipples; relatively small hands and feet; and/or an unusually small penis (micropenis) and/or undescended testes (cryptorchidism) in affected males.
Monosomy 18p is usually caused by spontaneous (de novo) errors very early in the development of the embryo that appear to occur randomly for unknown reasons (sporadically).
Children's Craniofacial Association
13140 Coit Road
Dallas, TX 75240
Support Organization for Trisomy 18, 13, and Related Disorders
2982 S. Union Street
Rochester, NY 14624-1926
March of Dimes Birth Defects Foundation
1275 Mamaroneck Avenue
White Plains, NY 10605
1825 K Street NW, Suite 1200
Washington, DC 20006
P.O. Box 751112
Limekiln, PA 19535
Chromosome Disorder Outreach, Inc.
P.O. Box 724
Boca Raton, FL 33429-0724
Chromosome 18 Registry & Research Society
7155 Oakridge Drive
San Antonio, TX 78229
American Heart Association
7272 Greenville Avenue
Dallas, TX 75231
UNIQUE - Rare Chromosome Disorder Support Group
P.O. Box 2189
Surrey, CR3 5GN
Craniofacial Foundation of America
975 East Third Street
Chattanooga, TN 37403
Genetic and Rare Diseases (GARD) Information Center
PO Box 8126
Gaithersburg, MD 20898-8126
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It is possible that the title of this topic is not the name you selected. Please check the Synonyms listing to find the alternate name(s) and Disorder Subdivision(s) covered by this report
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Last Updated: 4/10/2009
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