Experimental cerebral aneurysms in the female heterozygous Blotchy mouse

The Blotchy mouse is characterized by an X-linked inherited disorder of con nective tissue synthesis. The susceptibility to aneurysm formation in the c erebral arteries of the circle of Willis was compared in female heterozygou s 'Blotchy' and control mice subjected to unilateral carotid artery ligatio n either alone or associated with hypertension. Cerebral aneurysms develope d only in hypertensive Blotchy mice (6/31 vs. 0/30 in hypertensive controls ). Aneurysms of the aorta and its major branches occurred in normotensive m ice only in the Blotchy group in which hypertension increased the incidence of mesenteric and coeliac aneurysms. A light microscopic study of interrup tions of the internal elastic lamina (IIEL) showed that they developed in a rteries of both Blotchy and control mice but to a greater extent in the Blo tchy group where hypertension further increased their incidence, The IIEL i ncidence in the aortic arch varied in parallel to the occurrence of aneurys ms in all the different arterial sites. Thus, in an apparently normally via ble animal, the presence of a mutated gene which indirectly leads to defect ive elastin and collagen fibre synthesis, favours the formation of both per ipheral and cerebral aneurysms. However, the development of cerebral aneury sms requires the addition of an increase in haemodynamic stress.