TRIO and microcephaly: In humans, pathogenic variants in TRIO cause variable neurodevelopmental phenotypes with ASD features which can be mainly classified into two distinct forms of intellectual disability with micro- or macrocephaly: autosomal dominant intellectual developmental disorder 44, with microcephaly (MRD44, OMIM #617061), and autosomal dominant intellectual developmental disorder 63, with macrocephaly (MRD63, OMIM #618825).