Congenic rats for hypertension: how useful are they for the hunting of hypertension genes?

1. Linkage studies have revealed quantitative trait loci (QTL) for blood pressure in the rat genome using genetic hypertensive rat models. To identify the genes responsible for hypertension, the construction of congenic rats is essential. 2. To date, several congenic strains have been obtained from spontaneously hypertensive or Dahl salt-sensitive rats. The results of these studies should be interpreted according to whether the rats carry the whole QTL region or not. 3. After establishing congenic strains, three strategies are possible: (i) an orthodox positional cloning in which, using subcongenic strains, the QTL region is cut down to smaller fragments suitable for physical mapping; (ii) a positional candidate strategy in which candidate genes in the QTL regions are studied; or (iii) physiological studies in which intermediate phenotypes directly associated with the hypertension gene are explored. Several other experimental strategies are also available using congenic strains as new animal models for hypertension. 4. To make the most of advances in DNA technology, the precise evaluation of the phenotypic difference between congenic strains carrying different QTL or between a congenic and parental strain is critical.