In the fight against heart disease, gene-hunters follow trail from the Amish to Pakistan
The first clue came from serving milkshakes to the Amish.
For most people who drink a shake or eat a fat-laden meal, the blood becomes rich with fatty substances called triglycerides, and it stays that way for several hours.
In rural Lancaster County, a small percentage of the Plain People have the curious ability to clear these excess fats in short order. This discovery, by University of Maryland scientists in 2008, set off a worldwide quest for more such people, in hopes that this biological quirk could lead to a new wonder drug against heart disease.
Yet Dan Rader was puzzled.
The fat-clearing ability in the Amish had been traced to a mutation in just one copy of a gene on the 11th chromosome. So a person with that mutation on both copies of the gene would, in theory, have even lower levels of the fatty substance in the blood.
At Rader's lab at the University of Pennsylvania, and others, scientists analyzed hundreds of thousands of genomes in their databases, and came up empty. No one had two copies of the mutation.
"I thought maybe it was incompatible with life," he said.
Did having two copies of the mutation cause some grave, unrelated problem? Or, he wondered, was there such a thing as having triglycerides that were too low?
A genetic quest
The field of medicine has made tremendous strides in recent decades against coronary heart disease, marked by the dangerous buildup of waxy plaque inside the arteries. The rate of death was cut in half from 1963 to 1990, and then in half again by 2010, due to better emergency care, lower rates of smoking, and the use of cholesterol-lowering statin drugs, among other factors.
Yet heart disease remains a leading cause of death in the United States, killing hundreds of thousands each year. And scientists still have much to learn about the roles of cholesterol and triglycerides in human biology.
Rader, 57, chairman of the department of genetics at Penn's Perelman School of Medicine, is a firm believer that help lies in the genome.
The lanky, 6-foot-2 physician agrees that diet and exercise are important, and he bikes from his home in Center City to his office at Penn's 10-story Smilow Center for Translational Research.
"At least twice a day I get some exercise," he said.
But he believes that many patients need the added help of medication, and he is perennially on the hunt for better ones.
More than 70 genes have been linked to levels of LDL, or "bad," cholesterol, and a similar number are tied to triglycerides – though in both groups of genes, scientists understand the function of only a third of them, Rader said.
One of them has led to a newer class of injectable drugs, called PCSK9 inhibitors, that yield dramatic reductions in LDL levels. But they have been slow to catch on, with insurers balking at the price – more than $1,000 a month retail – and some physicians are concerned about side effects. The latest evidence suggests that one such drug, Amgen's Repatha, not only lowers cholesterol but also reduces the risk of heart attacks.
A clue from 7,000 miles away
Then there are triglycerides.
As with LDL, high levels of these fats are linked with heart disease, yet they also play an important role in the body – storing and transporting energy to the heart and other muscles.
There is debate about how to measure them. For the standard blood test, levels are assessed after the patient has fasted overnight. But recent research suggests that measuring the blood-borne fats after a meal may be a better indicator of a patient's ability to clear them.
The Amish people with the rare mutation, in a gene called APOC3, had lower baseline levels of triglycerides. And when they downed a milkshake, their levels rose by much less than in other people, and were cleared from the bloodstream more quickly. They also had less calcification in their arteries, suggesting that their unusual biology might protect against heart disease.
Was anyone better at it than the Amish?
In his quest, Rader learned from a friend about Danish Saleheen, a University of Cambridge graduate student who had launched a project to study the genetics of heart disease in his native Pakistan.
Heart disease is often perceived as a Western affliction, brought on by fast food and a sedentary lifestyle, yet it is a sizable problem in South Asia.
There was another reason that Saleheen had eyes on his home country: marriage between cousins is fairly common. That meant a greater chance that children would be born with identical copies of the same gene – the same version from mother and father.
Geneticists study the Amish for a similar reason. Marriage between cousins is not practiced, but certain genetic traits can become concentrated in the insular community.
If Saleheen were lucky, he would find "knockouts" – people in whom both copies of a gene were defective, allowing for some powerful science. One of the best ways to learn what something does is to study what happens when it is not there.
Saleheen and his colleagues collected blood samples from thousands of people, always carefully explaining the goals of the project in laymen's terms, a process that took up to an hour.
While the project was underway, in 2011, Rader helped recruit Saleheen to Penn and started collaborating with him on the analysis, along with others from Cambridge, Pakistan, and a host of other institutions.
The result was as good as they could have hoped.
The team discovered that in a Pakistani fishing village outside of Karachi, a handful of people had the same mutation as the Amish – not in one copy of the gene, but in both. Among them were a husband and wife and their nine children.
All had rock-bottom triglyceride levels, and all appeared to be in good health.
The University of Maryland's Toni Pollin, lead author of the original Amish study, is familiar with the findings, and is impressed.
"I think they really struck gold there," she said.
The drug pipeline
The research continues, as Rader, Saleheen, and their colleagues want to know about the long-term health of the people with these unusual genes. Will their arteries have lower degrees of calcification, like the Amish with one copy of the mutation? Are they less likely to develop heart disease?
Drug companies already have moved forward. Sparked by the initial research on the Amish, Ionis Pharmaceuticals has tested a drug that mimics their natural ability to clear fats from the blood stream.
In December, the Carlsbad, Calif., company announced that the drug led to sharp reductions in triglycerides for patients with extremely high levels, though not quite to the low levels found in Pakistan. Then in January, drug maker Novartis said it had entered into an agreement to license the drug.
Rader is optimistic. Meanwhile, the scientist in him wonders how the biology came about.
If it turns out to be so great to have ultralow levels of triglycerides, why is it so rare?
Rader speculated that for our ancestors, higher triglyceride levels might have played a protective role.
"People would often go for a few days before they caught the next antelope to eat," he said. "Maybe under situations of prolonged fasting, there's a benefit to not clearing your triglycerides as fast."
In the Amish, the mutation for rapid clearing of triglycerides goes back at least to the late 1700s, genealogy charts suggest, said Pollin, the Maryland researcher. But the genetic sequence appears to be far older than that, likely originating several hundred thousand years ago, and it is very possible that the Amish and the Pakistanis with the mutation have a common ancestor, she said.
Rader agrees. Ages ago, that person may have lived in a land of plenty, so it was OK to clear triglycerides from the bloodstream quickly. Today, if the science bears it out, their genetic legacy may yield yet another tool against heart disease.
Saleheen, an assistant professor of biostatistics and epidemiology at Penn, calls it "a gift of nature." In 2014, he went back to meet the man with nine children, both to confirm the initial finding and to tell him of the startling results.
"He was excited that he was someone unique in the world," Saleheen said. "He was more happy that his donation of the sample could help humanity at large."