A few years ago, a new genetic disorder (OMIM # 615075) has been associated with loss-of-function variations in the CTNNB1 gene. The clinical features include a delayed psychomotor development usually leading to severe intellectual disability with or without autistic spectrum disorders, progressive spastic diplegia, and various visual defects. Among over 30 cases described worldwide, 2 were reported with an exaggerated startle response to sudden stimulus corresponding to a very rare neurological phenomenon called hyperekplexia. The investigators also have a 3rd patient carrying a CTNNB1 syndrome associated with hyperekplexia.

Hyperekplexia can impair daily life because the affected person will fall unexpectedly and stiffly, causing repeated head- or body- wounds. It may be treated empirically by various drugs. Hyperekplexia has so far not been associated with CTNNB1 variations.

In this study, we aim to describe the prevalence and clinical characteristics of hyperekplexia in CTNNB1 syndrome carriers, in order to improve diagnosis and thus treatment.

The investigators will recruit CTNNB1 subjects through health care providers and also by contacting the families through dedicated social media and databases. The families and health care providers will be invited to fill in a questionnaire related to hyperekplexia (clinical, pharmacological, and genetic data).

Inclusion Criteria:

• Patient carrying a CTNNB1 syndrome showing an exaggerated startle response
• child whose parents have signed a consent form to participate in the study

Exclusion Criteria:

• Absence of molecular diagnosis
• Refusal to participate

CTNNB1 subjects