Hao-Fountain Syndrome (HAFOUS) is an extremely rare disorder that have been described in only around 70 families worldwide. The incidence and prevalence of the disorder is unknown. It is caused by mutations in the USP7 gene, a protein coding gene important for many cellular processes like tumor suppression and immune response, among others.

The clinical features of USP7 mutations include developmental delay/intellectual disability, autism spectrum disorder, increased prevalence of epilepsy, abnormal brain MRIs and speech/motor impairments, with some patients being completely non-verbal. 

The inheritance pattern of the disease caused by USP7 mutations is autosomal dominant, but to date the majority of documented cases are considered de novo mutations.