The present paper summarizes the possible roles of frequent and unfavourable genetic variants in cerebrovascular disorders, such as stroke and leukoaraiosis. It also approaches the topic theoretically from functional and mathematical points of view, which can help make the accumulating data on genetic variants more understandable. The interplay of an unfavourable genetic polymorphism and environmental clinical factors can result in a cerebrovascular disease or a state of vascular dementia. These constantly changing functional interactions need a highly specialised approach. There is, therefore, a great need to summarise the results on genetic polymorphisms concisely, and to discuss their special but shared features, which make their evaluation difficult with the methods used for the well-known Mendelian factors. The development of a correct approach to genetic polymorphisms may have a great impact on the understanding and prevention of cerebrovascular diseases.