Pontocerebellar hypoplasia type 4 (PCH4) is a very rare form of PCH, characterized by prenatal onset of polyhydramnios and contractures followed by hypertonia, severe clonus, primary hypoventilation leading to an early postnatal death. The disease is MONDO_0009166 (pontocerebellar hypoplasia type 4). Also known as: PCH4, fatal infantile encephalopathy with olivopontocerebellar hypoplasia, olivopontocerebellar hypoplasia.