Genetics is the determinism of our age (“Your destiny is determined by your genes”). It appears more scientific than the determinisms of previous ages such as astrology (“Your destiny is in the stars”) or Marxism (“Your destiny is in economics”), and thus has much greater appeal to the people who look to science for The Answers. News headlines breathlessly report the discovery of the “gene for” this behavior or that behavior: the gene for losing your virginity early, the gene for adultery, the gene for lying. What the headlines leave out are the subtleties: yes, our genetics have an influence our behaviors and decisions, but they are not “determinative” in any sense that that word is commonly understood. The same holds true for the genetics of many diseases: genes for things like diabetes and heart disease and high blood pressure and even breast cancer can increase or decrease the likelihood that someone will develop that disease, but are not “determinative.” Many, many factors other than genetics also play a role in developing these diseases.
However, there are some diseases for which the genes do seem to be determinative; that is, if you have certain genes for a condition, you will inevitably develop that condition. Such genetic disorders are called “fully penetrant.” In these cases, destiny does seem to be in the genes . . .
Or maybe not? In a study published earlier this month in Nature Biotechnology, researchers combed through 589,306 genomes obtained from genomic databases such as 23andMe. In so doing, they found thirteen people who have the genes for eight fully-penetrant, usually lethal, childhood-onset disorders; but the adults with those genomes are healthy adults, without the disorders their genes code for.