Proximal 18q deletion syndrome is a chromosomal condition that occurs when a piece of the long (q) arm of chromosome 18 is missing. The term "proximal" means that the missing piece occurs near the center of the chromosome. Individuals with proximal 18q deletion syndrome have a wide variety of signs and symptoms. Because only a small number of people are known to have this type of deletion, it can be difficult to determine which features should be considered characteristic of the disorder.

Most people with proximal 18q deletion syndrome have delayed development of skills such as sitting, crawling, walking, and speaking, and intellectual disability that can range from mild to severe. In particular, vocabulary and the production of speech (expressive language skills) may be delayed. Recurrent seizures (epilepsy) and weak muscle tone (hypotonia) often occur in this disorder. Affected individuals also frequently have neurodevelopmental disorders such as hyperactivity, aggression, and autism spectrum disorder that affect communication and social interaction.

Deletions from the q arm of chromosome 18 occur in an estimated 1 in 55,000 newborns worldwide. However, only a small number of these individuals have deletions in the region associated with proximal 18q deletion syndrome. At least 15 people with proximal 18q deletion syndrome have been described in the medical literature.

Proximal 18q deletion syndrome is caused by a deletion of genetic material from one copy of chromosome 18. The deletion occurs near the middle of the q arm of the chromosome, typically in an area between regions called 18q11.2 and 18q21.2. The size of the deletion varies among affected individuals. The signs and symptoms of proximal 18q deletion syndrome are thought to be related to the loss of multiple genes from this part of chromosome 18. Researchers are working to determine how the loss of specific genes in this region contributes to the various features of this disorder.

Genetic Testing Information

• Genetic Testing Registry: Deletion of long arm of chromosome 18

Genetic and Rare Diseases Information Center

• Proximal chromosome 18q deletion syndrome

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Catalog of Genes and Diseases from OMIM

• CHROMOSOME 18q DELETION SYNDROME

Scientific Articles on PubMed

• PubMed

• Buysse K, Menten B, Oostra A, Tavernier S, Mortier GR, Speleman F. Delineation of a critical region on chromosome 18 for the del(18)(q12.2q21.1) syndrome. Am J Med Genet A. 2008 May 15;146A(10):1330-4. doi: 10.1002/ajmg.a.32267. Citation on PubMed
• Cody JD, Sebold C, Malik A, Heard P, Carter E, Crandall A, Soileau B, Semrud-Clikeman M, Cody CM, Hardies LJ, Li J, Lancaster J, Fox PT, Stratton RF, Perry B, Hale DE. Recurrent interstitial deletions of proximal 18q: a new syndrome involving expressive speech delay. Am J Med Genet A. 2007 Jun 1;143A(11):1181-90. doi: 10.1002/ajmg.a.31729. Citation on PubMed
• Imataka G, Ohwada Y, Shimura N, Yoshihara S, Arisaka O. Del(18)(q12.2q21.1) syndrome: a case report and clinical review of the literature. Eur Rev Med Pharmacol Sci. 2015 Sep;19(17):3241-5. Citation on PubMed
• Kotzot D, Haberlandt E, Fauth C, Baumgartner S, Scholl-Burgi S, Utermann G. Del(18)(q12.2q21.1) caused by a paternal sister chromatid rearrangement in a developmentally delayed girl. Am J Med Genet A. 2005 Jun 15;135(3):304-7. doi: 10.1002/ajmg.a.30727. Citation on PubMed
• McEntagart M, Carey A, Breen C, McQuaid S, Stallings RL, Green AJ, King MD. Molecular characterisation of a proximal chromosome 18q deletion. J Med Genet. 2001 Feb;38(2):128-9. doi: 10.1136/jmg.38.2.128. No abstract available. Citation on PubMed or Free article on PubMed Central
• Tinkle BT, Christianson CA, Schorry EK, Webb T, Hopkin RJ. Long-term survival in a patient with del(18)(q12.2q21.1). Am J Med Genet A. 2003 May 15;119A(1):66-70. doi: 10.1002/ajmg.a.10217. Citation on PubMed