The long term objectives of the proposed research are athe identification of disease-causing genes an the characterization of their pathogenetic mechanism in hypertensive cerebrovascular disease. Hypertensive cerebrovascular disease is a major cause of stroke, and the third leading cause of death and disability in our society. While elevated blood pressure is an important risk factor, there is increasing evidence that other, blood pressure-independent, genetic factors play an significant role int he pathogenesis of cerebrovascular disease. Epidemiologic data suggest that the disease is inherited as a polygenic, quantitative trait, similar to primary hypertension. The complexity of polygenic diseases in man, accentuated by their heterogeneous and multifactorial nature, discourages attempts aimed at identifying disease-related genes or loci in humans. Alternatively, inbred animal strains showing the trait of interest as a genetically determine phenotype, represent a useful approximation, the study of which may reveal information that subsequently can be applied to human disease. We propose, therefore, to use the stroke-prone, spontaneously hypertensive rat (SHRSP), an experimental animal that is genetically predisposed to develop hypertensive cerebrovascular disease in a manner closely resembling human pathology, as a model that allows studies in which some of the confounding factors invariably present in humans can be avoided. Following the paradigm of cosegregation analysis for the dissection of disease-relevant genetic loci, we will establish an F2 intercross cohort by breeding the SHRSP with the spontaneously hypertensive rat (SHR), another hypertensive animal strain that, however, does not develop stroke. This strategy removes blood pressure, an important confounding variable, from the analysis, and provides a hybrid population in which the tendency towards stroke shows variation according tot he relative dosage of stroke-relevant genes that a given individual has received as a result of free segregation of alleles, while blood pressure, in contrast, shows minimal variation, as we have shown in preliminary studies. This algorithm provides a powerful approach to search for pathogenetically important genes, and also, in contrast to comparative studies, the only one that establishes causality between gene and phenotype. The proposed studies will pursue the following specific aims; (i) Preliminary studies demonstrate the SHRSP, but not SHR, when fed a specific diet (elements of which have also been shown in epidemiologic studies to increase the risk for stroke in man, show a high, early incidence of stroke, yet blood pressures are identical to SHR. An F2 hybrid cohort prepared by crossbreeding the two strains will be phenotypically characterized with regard to stroke, using latency until stroke as the major discriminating phenotype parameter. (ii) In addition to a moderate number of genetic markers already identified as polymorphic among SHR and SHRSP, a broader mapping panel will be generated using several complimentary approaches, including the development of new microsatellites, point mutation polymorphisms, and RAPD typing. In addition, polymorphic markers for a limited number of candidate genes will be developed. (iii) DNA prepared from the SHRSP/ SHR cross will be genotyped using the panel of polymorphic markers prepared and linkage analysis performed. (iv) If linkage to a marker is established, a variety of molecular and classical genetic approaches will be entertained, including the development of new, more densely spaced markers in the region of interest (e.g. by chromosome jumping) and the breeding of congenic lines.
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