KBG 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.

KBG syndrome is a rare genetic disorder. The name derives from the initials of the surnames of the first three families in whom the syndrome was described. It is generally inherited in an autosomal dominant manner, with most cases resulting from a de novo pathogenic variant, although inherited cases occur. A distinctive presentation may include the combination of macrodontia of the permanent upper central incisors, widely spaced eyes, and characteristic skeletal abnormalities.

It can present with psychiatric features such as ADHD, autism spectrum disorder (ASD), anxiety, obsessive or perseverative behaviors, behavioral dysregulation, and difficulties with social interaction. Hyperactivity, aggression, poor concentration, and difficulty adapting when routines change may also occur. Cognitive impairment, developmental delay, and speech and language impairment are common, with speech development often particularly delayed. Neurobehavioral difficulties may persist into adulthood, although some affected adults achieve substantial independence.

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

  • Triangular face

  • Synophrys

  • Widely spaced eyes

  • Prominent nasal bridge

  • Bulbous nose

  • Long philtrum

  • Brachydactyly

  • Clinodactyly of fifth fingers

Other characteristic features include short stature, skeletal abnormalities, and dental abnormalities, particularly macrodontia of the permanent upper central incisors. Skeletal manifestations may include scoliosis, costovertebral abnormalities, cervical ribs, delayed bone age, and coccygeal abnormalities. Neurologic manifestations may include seizures/epilepsy, abnormal electroencephalographic findings, and structural brain abnormalities. Additional reported features include feeding difficulties, gastroesophageal reflux, hearing impairment and recurrent otitis media, palatal abnormalities, congenital heart defects, cryptorchidism in males, strabismus and refractive errors, and premature or advanced puberty. Movement disorders, including ataxia, tremor, and dystonia, may also occur.

Early diagnosis is important to identify and monitor potentially significant neurologic, developmental, behavioral, skeletal, dental, auditory, ophthalmologic, gastrointestinal, cardiac, and endocrine complications, recognize neuropsychiatric needs early, and institute tailored multidisciplinary surveillance and treatment. In particular, ongoing assessment of development, educational needs, behavior, hearing, vision, growth, puberty, and seizure risk is recommended.

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.