Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I’m Dr F. Perry Wilson from the Yale School of Medicine.

The issue I’m discussing this week is bound to be sensitive, so let me try to focus just on the facts. Yes, there are more diagnosed cases of autism now than there have been in the past.

The US Secretary of Health and Human Services (HHS), Robert F. Kennedy, Jr, cites that fact and suggests that it implies the existence of an environmental cause of autism— as of yet unidentified — that, through careful research, can be identified, perhaps as early as September. The focus on an environmental explanation for the increase runs counter to a recent Centers for Disease Control and Prevention (CDC) report suggesting that the increase is due to better and earlier identification. RFK Jr referred to that line of evidence as a “canard” — a useful excuse to protect entrenched interests that are actually the culprits. And although I think we know what entrenched interests he may be referring to, I’ll give him credit that his public statements keep an open mind about what environmental factors might be at play.

I thought, therefore, that it might be a good time to look at what we already know about environmental versus genetic triggers for autism to set expectations on what an HHS-sponsored investigation may be able to find. In other words, let’s look at the data. Autism: genes vs environment.

There’s a pretty interesting way to quantify how much of a disease may be due to things external to our genetic makeup vs inherent to that makeup: twin studies. And the cool thing is, these studies can tell us how much of a disease may be due to an environmental trigger even when we don’t know what that trigger might be.

. . .