Whether arterial fragility is more frequent in patients with a helical mutation located near the N-proteinase cleavage site remains to be determined, since aortic root dilatation, arterial dissection, and coronary and cerebral artery aneurysms are occasionally encountered in patients with mutations in other parts of the COL1A1 or COL1A2 gene, although, in general, they are infrequent [15-17]. The gene discussed is COL1A1; the disease is Dilatation of the cerebral artery.