Genetically low HDL not tied to heart disease

By Anthony J. Brown, MD

NEW YORK (Reuters Health) - Lower levels of heart-healthy HDL cholesterol resulting from a gene mutation is not associated with an increased risk of heart disease involving ischemia -- restriction of blood flow through the coronary arteries, according to a study.

This suggests that low HDL, in and of itself, is not a heart disease risk factor.

A number of studies have tied low blood levels of HDL (the "good" cholesterol) to an increased risk of ischemic heart disease. However, whether HDL cholesterol is a primary factor in the development of heart disease is unclear, in part because of other factors related to low HDL cholesterol levels, such as harmful triglycerides, which may contribute independently to increases in heart and vascular events.

Dr. Anne Tybjaerg-Hansen, from Copenhagen University Hospital, Denmark and colleagues studied a group of patients with mutations in the ABCA1 gene causing reductions in HDL cholesterol levels but not increases in triglyceride levels.

Studying patients with genetic disorders that lower HDL cholesterol without increasing harmful triglycerides is an "ideal" way in which to assess the consequences of isolated, lifelong low HDL cholesterol levels, they note in the Journal of the American Medical Association.

"The principal finding," they say, is that mutations in ABCA1 associated with "substantial, lifelong lowering of plasma levels of HDL cholesterol, but not with corresponding higher levels of plasma triglycerides or atherogenic remnant lipoproteins, did not predict an increased risk of (heart disease)."

"Individuals with isolated low HDL cholesterol without elevated triglycerides and remnant lipoproteins," Tybjaerg-Hansen told Reuters Health, "may not benefit from treatment, because our study suggests that HDL cholesterol alone is not causally related to risk of ischemic heart disease."

SOURCE: Journal of the American Medical Association, June 4, 2008.