"Typically small remnants of the cerebellum are present, including cerebellar peduncles and vermian lobules, and as such the term subtotal cerebellar agenesis is often used. Cerebellar agenesis or hypoplasia has previously been referred to as Chiari IV malformation, however this term is now considered obsolete 1,2."
"While one might expect these individuals to mainly show motor coordination difficulties, the plasticity of the brain is such that motor issues, although present, are not necessarily as severe as in patients with cerebellar lesions acquired after birth. Patients with cerebellar agenesis do however display varying degrees of cognitive impairment in memory, behaviour, language and social functioning, and often autism or autism-like behaviour is encountered."