Linkage of the Angiotensinogen Gene to Essential Hypertension

Caulfield M, Lavender P, Farrall M, Munroe P, Lawson M, Turner P, Clark AJ

BACKGROUND
The renin-angiotensin system is a powerful pressor system with a major influence on salt and water homeostasis. Angiotensinogen (also called renin substrate) is a key component of this system; it is cleaved by renin to yield angiotensin I, which is then cleaved by angiotensin-converting enzyme to yield angiotensin II. The observation that plasma angiotensinogen levels correlate with blood pressure and track through families suggests that angiotensinogen may have a role in essential hypertension. We therefore investigated whether there is linkage between the angiotensinogen gene on chromosome 1q42-43 and essential hypertension.

METHODS
Samples of DNA from 63 white European families in which two or more members had essential hypertension were tested for linkage of the angiotensinogen gene to this disorder. Affected cousins, nephews, nieces, and half-siblings were included when possible. To test for linkage, we used as a marker a dinucleotide-repeat sequence flanking this gene, and we employed the affected-pedigree-member method of linkage analysis. Two molecular variants of the angiotensinogen gene, one encoding threonine instead of methionine at position 235 (M235T) and the other encoding methionine rather than threonine at position 174 (T174M), were also tested for possible association with essential hypertension.

RESULTS
We found significant linkage (t = 5.00, P < 0.001) and association (chi-square = 53.3, P < 0.001) of the angiotensinogen-gene locus to essential hypertension in the 63 multiplex families. This linkage was consistently maintained in the subgroup of subjects with diastolic pressure above 100 mm Hg and in the subgroups classified according to sex. It has been proposed previously that T174M and M235T are associated with essential hypertension. However, we found no association in our population between either polymorphism and this disorder.

CONCLUSIONS
This study provides strong and consistent support for the linkage to essential hypertension of regions within or close to the angiotensinogen gene. Precisely how mutations in this region may result in hypertension remains to be determined.

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