DEAR DR. ROACH: I often hear people say that an inherited/genetic disease skips a generation. This is in reference to any disease, from dementia, to breast cancer, to substance abuse, to rheumatoid arthritis (RA). I ask this because my wife’s mother had severe RA, yet my wife and her sister don’t show any signs of RA. Now, our daughter, at 35, has been diagnosed with RA. Is there any proven research that suggests genetic diseases skip a generation? Or is that just an old wives’ tale? — K.H.
ANSWER: I have respect for the old wives, since there is often a great deal of wisdom passed down through the ages. In the case of RA, a person who has a parent with RA is more likely to get it themselves than a person who has a grandparent with RA. Still, it is more common for RA to skip a generation than it is to show up without any family history at all.
There are several reasons a disease may skip a generation. Autosomal recessive conditions often do so. Sex-linked conditions are often “hidden” in females, but show up in their male offspring. A concept called variable penetrance may also explain why diseases skip generations.
There are more than 100 areas within the DNA that impact a person’s risk for developing RA, so the situation is very complex, much more so than the single genes most people learn in school.
