Deletion 18p syndrome (18p- syndrome)

Page most recently updated 7 September 2026

This page focuses on the reported psychiatric associations, which may be the initial presenting manifestation, and on other clinical features that may assist the psychiatrist or primary care physician in identifying the underlying diagnosis, considered through the lenses of the diagnostic lenses framework.

Deletion 18p syndrome (18p- syndrome) is a rare genetic disorder caused by deletion of part of the short arm of chromosome 18. It can occur as an inherited or de novo genetic condition, so absence of a relevant family history does not exclude the diagnosis. Most cases arise de novo, although inherited cases can occur. A distinctive presentation may include the combination of ptosis or epicanthus, protruding ears, intellectual difficulties, and short stature.

It can present with psychiatric features such as anxiety, behavioral difficulties, and social or emotional difficulties. ADHD and autism spectrum disorder (ASD) have also been reported, although these are not considered defining features of the syndrome. Obsessive-compulsive symptoms, including obsessive-compulsive disorder (OCD), have also been described. Cognitive impairment, developmental delay, learning difficulties, and speech and language impairment may also occur. Psychiatric manifestations are generally recognized during childhood or development, although anxiety and other behavioral or emotional difficulties may persist into adulthood.

From a morphologic lens perspective, other features include (but are not limited to):

  • Microcephaly

  • Round face

  • Micrognathia

  • Epicanthus

  • Ptosis

  • Protruding ears

  • Depressed nasal bridge

  • Downturned corners of mouth

  • Wide mouth

Other characteristic features include hypotonia, growth abnormalities, and neurologic abnormalities, including seizures/epilepsy and structural brain abnormalities. Ophthalmologic features may include strabismus and refractive errors, while hearing impairment may also occur. Additional reported features include cardiac abnormalities, renal and genitourinary abnormalities, skeletal abnormalities, and endocrine abnormalities, including growth hormone deficiency and thyroid abnormalities. Feeding difficulties, constipation, and dental abnormalities may also occur.

Early diagnosis is important to identify and monitor potentially serious neurologic, cardiac, ophthalmologic, endocrine, and developmental complications, recognize neuropsychiatric needs early, and institute tailored multidisciplinary surveillance and treatment.

Selected references and further reading — Morphologic lens

Jones KL, Jones MC, del Campo M. Smith's recognizable patterns of human malformation. 8th ed. Philadelphia: Elsevier; 2021.

Reardon W. The bedside dysmorphologist: a guide to identifying and assessing congenital malformations. 2nd ed. Oxford: Oxford University Press; 2016.

Allanson JE, Biesecker LG, Carey JC, Hennekam RCM. Elements of morphology: introduction. Am J Med Genet A. 2009;149A(1):2-5. doi:10.1002/ajmg.a.32601.

Hennekam RCM, Biesecker LG, Allanson JE, Hall JG, Opitz JM, Temple IK, Carey JC; Elements of Morphology Consortium. Elements of morphology: general terms for congenital anomalies. Am J Med Genet A. 2013;161A(11):2726-2733. doi:10.1002/ajmg.a.36249.