Deletion 18q Syndrome (Long arm 18 Deletion Syndrome, 18q- 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 18q syndrome (Long arm 18 deletion syndrome, 18q- syndrome) is a rare genetic disorder caused by deletion of part of the long 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 midface retrusion, prominent antihelix, and whorl digital pattern.

It can present with psychiatric features such as anxiety, depression, behavioral dysregulation, irritability, and ADHD. Autism spectrum disorder (ASD) has also been reported. Bipolar disorder and psychotic disorders have been described, although these are not characteristic features of the syndrome. Cognitive impairment, developmental delay, learning difficulties, and speech and language impairment are common. Psychiatric manifestations may emerge during childhood or development, although mood and anxiety disorders and other neuropsychiatric difficulties may persist into adulthood or be diagnosed later.

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

  • Microcephaly

  • Midface retrusion

  • Depressed nasal bridge

  • Downturned corners of mouth

  • Short metacarpal – first metacarpal with proximal placement of thumb

  • Single transverse palmar crease

Other characteristic features include hypotonia, seizures/epilepsy, and abnormalities of myelination, with delayed or abnormal myelination being a distinctive neurologic feature. Hearing impairment, including narrowing or absence of the ear canals, and ophthalmologic abnormalities such as strabismus and refractive abnormalities may occur. Additional reported features include short stature, often associated with growth hormone deficiency; thyroid abnormalities including hypothyroidism; congenital heart defects; renal and genitourinary abnormalities; skeletal and foot abnormalities; cleft palate; feeding difficulties; and skin abnormalities.

Early diagnosis is important to identify and monitor potentially serious neurologic, cardiac, endocrine, auditory, and ophthalmologic 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.