A related neurodevelopmental disorder characterized by DD/ID, progressive microcephaly, failure to thrive, and periventricular heterotopia has been linked to biallelic inactivating variants of ARFGEF2 (ARPHM, MIM: 608097)16, encoding ARF-specific GEF stimulating the GTPase activation. This evidence concerns the gene CDKN2A and periventricular nodular heterotopia.