Could a Genetic Mutation Lower Your Risk of Coronary Artery Disease?
Sometimes a phrase catches one’s eye, for example the beginning of a recipe in Mrs Beeton’s Victorian cookbook: "Take a dozen eggs…" In like manner, a phrase in a paper in a recent edition of the New England Journal of Medicine caught my eye: "Five obese rhesus monkeys…" Perhaps they – the monkeys - had been following Mrs Beeton’s directions too closely.
The phrase that caught my eye was in the middle of an interesting paper about the genetics and biochemistry of coronary artery disease. Although the disease is in sharp decline throughout the western world for reasons yet to be fully explained, it remains a major cause of death, and therefore research into its causes, prevention and treatment remains a high priority.
The researchers in this paper, which was refreshingly unusual in combining epidemiological with experimental work, attempted to show that a certain genetic mutation found in the human population (or at least the population of European descent) was statistically associated with a reduced level of triglycerides in the blood, which in turn was associated with a reduced risk of developing coronary artery disease. They then went on to show that the biochemical change in which the genetic mutation resulted could cause reduced levels of triglycerides in mice and the five fat monkeys mentioned above.
The authors first showed that 1,661 patients with the mutation that is believed to result in lower levels of triglycerides in the blood had a lower prevalence of coronary artery disease than 41,269 patients who did not have it. Their risk of the disease was 19 percent lower than that of those who did not have the mutation.
They also showed that those with the mutation also had lower levels of triglycerides in total, but higher levels of high-density lipoprotein (thought to be protective against coronary artery disease).
They then showed that only one in 811 patients with coronary artery disease (as proved by coronary arteriogram) had the mutation while one in 503 patients without the disease had it.
Statistical correlation does not by itself mean that two variables have a causal relationship in either direction (that a causes b or that b causes a). Intelligence and large feet are correlated, for example, but that does not prove that intelligent people think with their feet. That correlation does not mean causation is both elementary and constantly reiterated. It has to be reiterated because it is so often forgotten.