A New Serum Type System in Man — the Lp System

This is where lipoprotein(a) begins. In 1963, the Norwegian geneticist Kåre Berg described a previously unknown inherited variation in human serum — what he called the “Lp system” — that some people carried and others did not.

Working before the molecular tools that would later explain it, Berg recognized the essentials by careful observation: the new antigen was attached to the beta-lipoprotein fraction, it was present in roughly a third of people of European descent, and it followed a pattern of genetic inheritance. He had, in effect, discovered Lp(a) and correctly identified it as a heritable trait — a finding that would take decades for the field to connect to cardiovascular disease.

Its place in this library is historical, and that is precisely its significance. Everything written since about Lp(a) as a genetically fixed, causal cardiovascular risk factor descends from this paper. What Berg catalogued as a serum curiosity is now understood to silently raise the risk of heart attack, stroke, and aortic stenosis in one in five people.

We rate the evidence moderate by modern standards — it is a descriptive report from an earlier era — but its clinical significance is among the highest here, as the origin point of an entire field of cardiovascular genetics.