Clinical characteristics: EXOSC3 pontocerebellar hypoplasia (EXOSC3-PCH) is characterized by abnormalities in the posterior fossa and degeneration of the anterior horn cells. At birth, skeletal muscle weakness manifests as hypotonia (sometimes with congenital joint contractures) and poor feeding. In persons with prolonged survival, spasticity, dystonia, and seizures become evident. Within the first year of life respiratory insufficiency and swallowing difficulties are common. Intellectual disability is severe. Life expectancy ranges from a few weeks to adolescence. To date, 82 individuals (from 58 families) with EXOSC3-PCH have been described.
Diagnosis/testing: The diagnosis of EXOSC3-PCH is suspected in children with characteristic neuroradiologic and neurologic findings, and is confirmed by the presence of biallelic EXOSC3 pathogenic variants identified by molecular genetic testing.
Management: Treatment of manifestations: No specific therapy is available. Treatment is symptomatic. Contractures and scoliosis are managed by passive or active movement and bracing as needed. Aspiration risk and seizures are managed in a routine manner. Education is adapted to the level of cognitive abilities.
Surveillance: Regular examinations to address: growth and nutritional status (including problems with feeding and risk of aspiration); respiratory function; joint contractures and scoliosis. Observation for and management of epileptic seizures.
Genetic counseling: EXOSC3-PCH is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an EXOSC3 pathogenic variant, each sib of an affected individual has at conception a 25% chance of inheriting both pathogenic variants and being affected, a 50% chance of inheriting one pathogenic variant and being an unaffected carrier, and a 25% chance of inheriting both normal alleles. Once the EXOSC3 pathogenic variants have been identified in an affected family member, prenatal and preimplantation genetic testing are possible.
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