These considerations have major implications on studies into the genetics of hypertension. A qualitative trait of “hypertension” could be subject to classic Mendelian laws of inheritance whereas a continuous “blood pressure” trait would constitute a non-Mendelian complex trait [6]. The normal unimodal distribution of blood pressure in the general population supports the latter [7]. However, there are rare monogenic Mendelian forms of hypertension which demonstrate that at least some forms of hypertension and possibly even some components of blood pressure could be explained by classic Mendelian inheritance [6]. From family and twin studies heritabilities of systolic and diastolic blood pressure are generally estimated in the range of 15 to 40% and 15 to 30%, respectively [8], [9] and [10]. The sibling recurrent risk of hypertension is in the range of 1.2 to 1.5 [11]. However, these figures are influenced by non genetic factors including shared environment and measurement errors so that the magnitude of the genetic effect could be different.