Our sample of 91 affected resistant hypertensive African Americans represents an extreme sampling approach from the upper tail of the distribution of blood pressure response to antihypertensive drugs from a large RCT. We have defined our phenotype as a more extreme version of resistant hypertension: our 91 subjects were all taking 4 or more medications to lower blood pressure and had blood pressure values greater than 140/90 mmHg after four years in the RCT.