Moreover, seven patients with sporadic CM-AVM have been shown to carry a RASA1 mosaic variant in lesional tissue [35,36,37] and, in one case, an additional variant both in the blood and in the malformation [35], suggesting that the two-hit hypothesis may also hold valid for sporadic cases of PWS and CM-AVM. Here, RASA1 is linked to Prader-Willi syndrome.