ADGRG1 and polymicrogyria: In addition to identifying a known disease-causing mutation in the ADGRG1/GPR56 polymicrogyria gene in two of the four available affected members, the remaining two available affecteds both have a biallelic mutation in the retinol dehydrogenase gene, RDH14. MRI analysis from these two individuals at ages 20 months and 14 years suggests a progressive childhood-onset form of cerebellar atrophy, in addition to ID.