1p36 deletion syndrome (Monosomy 1p36 deletion 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.

1p36 deletion syndrome (Monosomy 1p36 deletion syndrome) is a rare genetic disorder caused by deletion of part of the short arm of chromosome 1. 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 deep-set eyes, pointed chin, and large anterior fontanel.

It can present with psychiatric features such as ADHD, behavioral dysregulation, temper tantrums, aggression, self-injurious behavior, and sleep difficulties. Autism spectrum disorder (ASD) has also been reported, although the psychiatric phenotype remains incompletely characterized. Cognitive impairment, developmental delay, learning difficulties, and marked speech and language impairment are common, with some individuals having very limited or absent expressive language. These manifestations generally emerge during childhood or development, although behavioral and neuropsychiatric difficulties may persist into adolescence and adulthood.

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

  • Microcephaly

  • Flat occiput

  • Prominent forehead

  • Deeply set eyes

  • Almond-shaped palpebral fissure

  • Depressed nasal bridge

  • Long philtrum

Other characteristic features include hypotonia, seizures/epilepsy, and structural brain abnormalities. Ophthalmologic and auditory manifestations may include visual impairment, strabismus, and hearing loss. Additional reported features include congenital heart disease and cardiomyopathy, growth abnormalities, feeding and swallowing difficulties, skeletal abnormalities, renal and genitourinary abnormalities, and hypothyroidism.

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