Mucoid dysplasia of tricuspid and congenital bicuspid aortic valves in Syrian hamsters (Mesocricetus auratus).

A histological study was made of the aortic valves of 141 Syrian hamsters aged between 35 and 657 days, belonging to an inbred laboratory colony with a high incidence of congenital bicuspid aortic valves. A tricuspid aortic valve was found in 81 specimens, whereas the remaining 60 possessed a bicuspid aortic valve. In all bicuspid valves there were two aortic sinuses, a ventral and a dorsal, each supporting one cusp. Thirty-three (23.4%) of the 141 specimens showed mucoid dysplasia of the aortic valve. The defect was characterized by thickening of the valve cusps and disruption of the fibrosa layer accompanied by an increased amount of glycosaminoglycans. Ten (12.3%) of the 81 tricuspid aortic valves and 23 (38.3%) of the 60 bicuspid aortic valves were dysplastic. This difference was statistically significant (P < 0.001). The findings indicate that, in the Syrian hamster, the simultaneous occurrence of bicuspid aortic valve and aortic valve dysplasia is not a random event. However, the fact that these valve defects also occur independently suggests that there is no primary morphogenetic dependence between them, but that some other cause predisposes to their concurrence.