IN A FEW CASES A SINGLE GENETIC MUTATION HAS BEEN DIRECTLY LINKED TO HEIGHTENED ATHLETICISM
Stephen M. Roth, an associate professor of kinesiology at Maryland, is among a group of scientists who track all the published work on potential performance genes and compiled a list known as the Human Gene Map for Performance. Roth notes that even seemingly straightforward athletic attributes, such as raw strength, are highly complex, influenced as they are by multiple genetic and environmental factors. "With any single gene that seems to have a positive effect on performance, the effect is very subtle," Roth says. There are, however, a few documented cases in which a single, rare genetic mutation has hugely increased an individual's athleticism.
• Eero Mäntyranta is a former cross-country skier who won three gold, two silver and two bronze medals for Finland in three winter Olympics in the 1960s. But suspicions of blood doping cast a pall over his achievements, because he had 20% more oxygen-carrying red blood cells than his competitors despite his claim that his training was no different from theirs. Three decades later, in 1993, Finnish scientists published the results of a study that examined five generations of his family. The study found that a rare mutation on the EPOR gene runs in the Mäntyranta family, causing an excessive response to erythropoietin, or EPO, a hormone that spurs red-blood-cell production. In essence, Mäntyranta and 28 relatives who were studied have naturally what some athletes gain only by cheating with EPO injections. Not surprisingly, the family has a number of accomplished endurance athletes.
• In 2000 a German doctor was startled by the leg-muscle definition of a newborn boy at the Charité hospital in Berlin. Four years later this so-called superbaby had calves and glutes far more developed than those of his peers, and he could hold a pair of 6.6-pound dumbbells at arm's length. Further study determined that a rare mutation on two genes prevents the child from producing myostatin, a protein that helps tell muscles when to stop growing. The boy's mother has the same mutation on one of her two myostatin genes, leaving her with some myostatin but less than an average person has. She is the only adult with a documented myostatin mutation to date, and she was a professional sprinter.
• In 1969 a quarter horse named Impressive was born with a mutation on a gene that affects the flow of sodium into muscle cells. That allowed Impressive's muscles to contract both more quickly and more fully than those of other quarter horses, and in 1974 it helped him win the Open Aged world championship, a first for his breed. Impressive was intensely sought for breeding, and he sired dozens of world champions.
Such rare gene mutations have downsides, however. Mäntyranta's condition can cause excess strain on the heart. As for the German superbaby, doctors can only wonder whether his condition will cause his muscles, including the heart, to grow bigger than is healthy. And Impressive's mutation can cause a disease called hyperkalemic periodic paralysis, which is potentially fatal. Because Impressive spread the mutation to so many horses, his condition is sometimes known as Impressive syndrome.