Salt-sensitive genes.

Salt-sensitive genes

There is currently no simple test for people with high blood pressure that would determine whether they can lower their blood pressure with a strict low-salt diet. Since such a diet would help only about half of them, convincing patients to cut their salt intake is a difficult task for doctors.

However, salt sensitivity can be determined by infusing subjects with high levels of saline and watching what happens, and researchers have used this method to correlate the condition with high levels of a blood protein. The protein may prove to be an easily measured marker, they say.

Judy Z. Miller and her colleagues at the Indiana University School of Medicine in Indianapolis used saline infusion in their study of 570 people, 192 of whom had high blood pressure. They measured various blood proteins, including one called haptoglobin that comes in two possible forms. They found that people who had all haptoglobin-1, meaning they had inherited a haptoglobin-1 gene from each parent, were 2.5 times as likely to be salt sensitive as people with the other type, haptoglobin-2. People with half haptoglobin-1 and half haptoglobin-2 fell in the middle.

What role, if any, haptoglobin-1 plays in hypertension remains to be determined. Both forms of the protein bind to hemoglobin, saving it from destruction by the kidneys. Since the kidneys play a key role in blood pressure maintenance, the proteins may exert an effect there. Or, it could be that their genes just happen to be near a gene that is directly involved.