OBSCURE CHOLESTEROL AS BAD AS COMMON TYPE, STUDY SAYS.

Byline: Associated Press 

A little known form of ``bad'' cholesterol that doctors cannot yet measure reliably may cause early heart disease just as often as its better known cousins, a study suggests.

The lesser-known culprit - called lipoprotein(a) - may lurk in dangerously high levels in the blood of people whose other cholesterol levels appear normal on routine tests, researchers say.

Excess levels of lipoprotein(a), which are particles of protein and fat in the blood, accounted for 10 percent of all cases of premature heart disease - those occurring before age 55 - among the 2,191 men studied, said Dr. Andrew G. Bostom, who led the work as a research fellow for the National Heart, Lung and Blood Institute.

The findings were published in today's issue of The Journal of the American Medical Association.

The study included women, but too few cases of premature heart disease developed to calculate their risk from Lp(a), presumably because estrogen protects premenopausal women from heart disease, Bostom said.

Bostom said it's too early to do widespread testing for Lp(a) levels because no standardized screening exists and because even when the Lp(a) level is known, very little can now be done to modify it. Unlike other kinds of cholesterol, Lp(a) levels are 95 percent determined by genes, so drugs and changes in diet affect them very little.

The value of knowing an excess Lp(a) level is that it may warn the patient of the need for more aggressive treatment of other traits that also predict heart disease: smoking, poor diet, high blood pressure, high blood sugar and high cholesterol of the type whose levels can be altered through diet or drugs.

People worried about heart disease should concentrate on those risk factors rather than worrying about Lp(a) because nothing can be done about it at present, the researchers said.

``Smoking just blows everything out of the water in terms of being a risk factor for premature coronary heart disease,'' Bostom said. He noted smoking accounted for 55 percent of cases of premature heart disease in the study.

Abnormal levels of two better known forms of cholesterol - HDL, or ``good'' cholesterol, and total cholesterol, a combination of all forms - each accounted for about 10 percent of premature heart disease in the study.

The participants began the study at ages 20 to 54 and were tracked for 15 years, until 1991. A total of 129 suffered premature heart disease, defined as a heart attack, poor blood flow to the heart, heart pain or sudden heart death.

An expert not associated with the study, Dr. Angelo Scanu, director of the Lipid Clinic at the University of Chicago, cautioned that scientists still do not fully understand the role of Lp(a).

For example, African-Americans have two to three times the rate of elevated Lp(a) compared with whites, yet they do not have double to triple the prevalence of premature heart disease, Scanu said.