Bi-allelic truncating mutations in PCDH12 have been reported in patients presenting with the Diencephalic–Mesencephalic Junction Dysplasia Syndrome 1 (MIM: 251280); or cerebral palsy combined with a neurodevelopmental disorder; and or cerebellar ataxia with retinopathy.
Most of the patients present with intellectual disability, speech impairment, epilepsy/seizure, and microcephaly. Movement disorders have been noticed in a large portion of patients, including ataxia and spasticity. Facial dysmorphisms are often present, including a broad nasal bridge, thick lower lip, and low-set ears. Brain anomalies have been observed in the majority of affected individuals, in particular the characteristic diencephalic–mesencephalic junction dysplasia, and brain calcifications or hyperechogenicity.
The table below reports in detail the clinical features observed so far (July 2021) in individuals with PCDH12 bi-allelic variants: 
PCDH12