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Condition report · Neurological

Hao-Fountain Syndrome

A rare neurodevelopmental disorder causing developmental delay, speech delay and intellectual disability, often with autism and behavioural differences. It is caused by a change or deletion affecting one copy of the USP7 gene.

A condition report looks for rare variants known to cause the conditions it covers.

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The condition we analyse

Autosomal dominant

Caused by a change in one copy of USP7, an enzyme that controls the stability of many proteins, including some involved in brain development. Changes can reduce or increase its activity, and they usually arise de novo.

Signs and symptoms

Developmental delay with speech delay, and intellectual disability that varies, with up to half of affected people having normal-range intellect. Autism, anxiety, aggression and other behavioural differences are common, as are low muscle tone, feeding difficulties and eye problems such as long-sightedness, squint or nystagmus. Less often there are seizures or underdeveloped genitals in males.

What a diagnosis changes

Developmental, speech, educational and behavioural support, with neurological and eye assessment and seizure treatment when needed. Most cases arise de novo, but genetic counselling and parental testing guide recurrence risk; rarely the change is inherited from a parent.

Genes analysed

Also known as

HAFOUS; USP7-Related Diseases

Includes 2 related subtypes ↓
  • Hao-Fountain syndrome due to 16p13.2 microdeletion
  • Hao-Fountain syndrome due to USP7 mutation
MONDO:0014805Orphanet 643549MedGen 1719035Sources: [1][3]

References

  1. Schaaf C, Sailer S, 2025. USP7-Related Hao-Fountain Syndrome. GeneReviews
  2. Chen H, Ferguson CJ, Mitchell DC, Risch I, Titus A, Paulo JA et al., 2025. The Hao-Fountain syndrome protein USP7 regulates neuronal connectivity in the brain via a novel p53-independent ubiquitin signaling pathway. Cell reports
  3. Korchak EJ, Sharafi M, Jaen Maisonet I, Salazar-Chaparro A, Semenova IV, Khan H et al., 2025. Functional spectrum of USP7 pathogenic variants in Hao-Fountain syndrome: Insights into the enzyme's activity, stability, and allosteric modulation. Proceedings of the National Academy of Sciences of the United States of America

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