X-Linked Intellectual Disability-Cerebellar Hypoplasia Syndrome

X-linked intellectual deficit-cerebellar hypoplasia, also known as OPHN1 syndrome, is a rare syndromic form of cerebellar dysgenesis characterized by moderate to severe intellectual deficit and cerebellar abnormalities.

Epidemiology

OPHN1 syndrome is very rare. To date, up to 12 families have been reported.

Clinical description

Affected male patients present moderate to severe intellectual disability, hypotonia, severe developmental delay, early-onset complex partial or tonic-clonic seizures, strabismus, dysmetria and occasionally ataxia. Cryptorchidism and genital hypoplasia have been reported. Some patients have abnormal behavior and a characteristic facial phenotype (long face, prominent forehead, infraorbital creases, deep-set eyes, upturned philtrum and large ears). Carrier females have been reported to have mild learning disabilities, mild cognitive impairment, strabismus, and subtle facial changes.

Etiology

Various mutations including deletions and splice site mutations in the OPHN1 gene (Xq12) have been reported in patients with this syndrome.

Diagnostic methods

Neuroradiological findings include posterior vermis dysgenesis, vermian parasagittal cleft, cerebellar hypoplasia, cortical atrophy, and enlargement of the cerebral ventricles. Molecular genetic testing is needed to confirm diagnosis.

Genetic counseling

Transmission appears to follow an X-linked semi-dominant pattern.