Mutations of the RASA1 gene (RASp21 protein activator 1; OMIM 139150) [6] (located on the chromosome 5q14.3) and transmitted in an autosomal dominant manner, are responsible for different forms of VMs (CMs, AVMs, AVFs), as single manifestations, or in complex combinations, as in the case of PWS [16,18]. The gene discussed is RASA1; the disease is Prader-Willi syndrome.