X-Linked Intellectual Disability, Najm Type

Najm type X-linked intellectual deficit is a rare cerebellar dysgenesis syndrome characterized by variable clinical manifestations ranging from mild intellectual deficit with or without congenital nystagmus, to severe cognitive impairment associated with cerebellar and pontine hypoplasia/atrophy and abnormalities of cortical development.

Epidemiology

Prevalence of this rare neurological syndrome is unknown. Up to 35 families have been reported to date.

Clinical description

Patients (mostly females) have been reported to have variable clinical manifestations including intellectual deficit, severe developmental delay, seizures, unsteady gait, sensorineural hearing loss and postnatal microcephaly (in most cases). Minor facial anomalies include: low or broad forehead, hypertelorism, long philtrum and micrognathia. Ocular findings are also variable and include congenital nystagmus, strabismus, cataracts, myopia or reduced visual acuity. Males appear to be more severely affected.

Etiology

Point mutations and deletions in the CASK gene (Xp11.4) have been found in patients with this syndrome.

Diagnostic methods

Magnetic resonance imaging (MRI) generally shows pontocerebellar hypoplasia/atrophy and simplified cortical gyri. Molecular genetic testing is needed to confirm diagnosis.

Genetic counseling

Transmission follows an X-linked dominant pattern.