The renin angiotensin system is a complex process involving hormones and enzymes that regulate blood volume and blood pressure. The hormone angiotensin II is responsible for making blood vessels narrow or constrict. Angiotensin II is found in the blood and can attach to special sites called receptors on blood vessel walls. These receptors are programmed to accept angiotensin II and cause a constriction of the blood vessel. This function is found in the genetic information of each individual person.

Occasionally patients have changes in their genes related to angiotensin II receptors. These changes may result in the receptors acting differently to angiotensin II, which may affect the function of blood vessels.

This study is designed to improve researchers understanding of the physiological effects on blood vessels associated with mutations of the genes responsible for angiotensin II receptor function.

Polymorphisms in the genes encoding for various elements of the renin angiotensin system have been associated with cardiovascular disease. We have isolated novel alleles in the angiotensin II type I receptor gene. We propose this exploratory investigation to study the physiological effect of these mutations on vascular function in patients and family members who carry these rare alleles.

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Patients aged 21 or older with chronic orthostatic intolerance will be included.

There will be no exclusion from participation in the study on the basis of ethnicity/race.

Patients will be recruited in the Cardiology Branch outpatient clinic, Dr. David Goldstein (Chief Neurocardiology Section, NINDS, NIH), or from outside physicians.

Children will be excluded from the study because of inability in obtaining informed consent.

Cognitively impaired individuals, prisoners, or other institutionalized persons will not be able to participate.