Duplication 9p syndrome (trisomy 9p 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.

Duplication 9p syndrome (trisomy 9p syndrome) is a rare chromosomal disorder caused by partial or complete duplication of the short arm of chromosome 9. It can occur as a de novo chromosomal change or as a result of an inherited parental chromosome rearrangement, so absence of a relevant family history does not exclude the diagnosis. A distinctive presentation may include widely spaced eyes and distal phalangeal hypoplasia.

It can present with psychiatric features such as behavioural difficulties and attention difficulties. Autism spectrum disorder (ASD) and psychotic behaviour have also been reported, although the evidence for a specific association remains limited. Neuropsychiatric manifestations are usually recognised during childhood, and there is a paucity of evidence regarding new-onset psychiatric manifestations in adulthood.

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

  • Macrocephaly

  • Widely spaced eyes

  • Epicanthus

  • Downslanted palpebral fissures

  • Downturned corners of mouth

  • Short palm

  • Clinodactyly of fifth fingers

  • Short metatarsals

  • Small nails

Other characteristic features include developmental delay or intellectual disability, speech and language impairment, seizures, and hypotonia. Skeletal and digital abnormalities may include short fingers and toes, hypoplasia of the middle or terminal phalanges, clinodactyly of the fifth fingers, and small or hypoplastic nails. Other manifestations may include short stature, congenital heart defects, renal abnormalities, and central nervous system abnormalities.

Early diagnosis is important to identify and manage potentially significant developmental, neurological, growth, cardiac, renal, skeletal, and other congenital complications; to provide appropriate developmental, educational, speech and language, and behavioural support; and to allow coordinated multidisciplinary management.

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.