CDC42 and Adams-Oliver syndrome: Recently gain-of-function mutations in the ARHGAP31 gene encoding a Cdc42/Rac1 regulatory protein have been reported in AOS [3], and two more cases of AOS were reported to harbor homozygous mutations in the DOCK6 gene, encoding a guanidine nucleotide exchange factor that activates Cdc42 and rac1 [4].