FG syndrome (Opitz-Kaveggia 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.

FG syndrome (Opitz-Kaveggia syndrome) is an X-linked genetic condition. It can occur as an inherited or de novo genetic condition, so absence of a relevant family history does not exclude the diagnosis. It occurs predominantly in males, while female carriers are typically unaffected. A distinctive presentation may include the combination of prominent forehead, hypotonia, and imperforate anus.

It can present with psychiatric features such as ADHD, anxiety, aggression, and behavioural difficulties. Communication difficulties may contribute to behavioural dysregulation. These behavioural manifestations may persist into adulthood, although the syndrome is usually recognised earlier because of intellectual disability and developmental difficulties.

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

  • Macrocephaly

  • Frontal upsweep

  • Prominent forehead

  • Midface retrusion

  • Widely spaced eyes

  • Short palpebral fissure

  • Epicanthus

  • Downslanted palpebral fissures

  • Thick vermilion

  • Syndactyly

  • Clinodactyly of fifth fingers

  • Broad thumbs and/or broad halluces

  • Prominent fingertip pads

  • Single transverse palmar crease

Other characteristic features include intellectual disability or developmental delay, constipation, and congenital abnormalities such as partial or complete agenesis of the corpus callosum, congenital heart defects, and anal anomalies. Seizures may occur, and musculoskeletal abnormalities such as scoliosis, joint hypermobility, or joint contractures may also be present.

Early diagnosis is important to identify intellectual, behavioural, neurological, cardiac, gastrointestinal, and other congenital complications; to support appropriate developmental, educational, and behavioural management; and to allow surveillance and management of seizures, constipation, cardiac abnormalities, and other medical complications.

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.