It turned out that the culprit was a little-known but very deadly type of particle called Lp(a) (pronounced “el-pee-little-A”). This hot mess of a lipoprotein is formed when a garden-variety LDL particle is fused with another, rarer type of protein called apolipoprotein(a), or apo(a) for short (not to be confused with apolipoprotein A or apoA, the protein that marks HDL particles). The apo(a) wraps loosely around the LDL particle, with multiple looping amino acid segments called “kringles,” so named because their structure resembles the ring-shaped Danish pastry by that name. The kringles are
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