Is there a genetic overlap?
Earlier this month, a study in the journal Molecular Psychiatry unearthed more information about the complex genetics of autism.
Researchers from Children’s Hospital of Philadelphia were zeroing in on changes to genetic sequences called “copy number variants” (CNV). Instead of being single alterations in DNA code, CNVs are missing or repeated stretches of code, dozens to hundreds of bases long. Sure enough, patterns emerged.
In the kids with autism, the team found certain CNVs that didn’t exist in the control group. Not only that, many of the deletions and repeats of DNA were in genes that regulate brain development, for example how synapses are formed (allowing neurons to talk to one another).
This isn’t the first time we’ve seen a link between CNVs and childhood disorders – the hunt is well known in ADHD research too. In fact, in an earlier study, the same team found a special set of CNVs in kids with ADHD – also in genes that affect nervous system wiring.
It’s also intriguing that both studies showed a genetic overlap between the two disorders; some of the DNA glitches in the ADHD and autism groups were in similar spots on the genome. One of the most notable crossovers researchers have found is on chromosome 16.
Does that mean the two childhood disorders are related?
Putting genes aside for a minute and looking at kids, we know that ADHD and autism are separate clinical conditions: under the autism umbrella, children have difficulty relating and communicating and often show repetitive or “stereotyped” behaviors. ADHD, however, takes the form of distractibility, difficulty focusing, and hyperactivity; ADHD kids seem to be “driven by a motor.”
But the story isn’t always so neat and tidy. Kids on the autism spectrum can also have trouble settling and focusing (especially outside their naturally driven interest), and kids with ADHD sometimes have trouble with social skills like turn-taking in conversation. Roughly 50 percent of kids on the autism spectrum also meet criteria for ADHD, although under the current diagnostic rules, you can’t technically have both. ADHD and autism appear to grow from different emotional and cognitive cores, but at the edges they can bleed together – a sometimes confusing and frustrating fact for parents as they try to wrap their heads around treatment options.
It’s not surprising, then, that when scientists search for genetic clues to each, they see points of commonality, DNA language that might, for example, affect pathways to the frontal lobes (the hub of empathy, emotional skill, and focus).
In fact, the more we learn, the more the overlap makes sense. Both disorders – particularly autism – are more complex than we ever imagined. In this last study, the team ran experiments on two separate populations and each time found 400 characteristic genetic hiccups in the autism population that did not appear in the controls. Studies like this indicate that literally hundreds of genes are at play in autism, and, astoundingly, a different combination could be at the root of each child’s case.
The majority of those genes are probably unique to autism – coding for small changes in the brain that make empathy or reading social cues more challenging, for example. But others may share brain space with ADHD – like those that make it more difficult for a child to sort out sensory information and lead to sensory overload (common for kids with both disorders).
That just shows you the limits of diagnostic labels: they pull together symptoms and give them a name, but they say nothing about what’s underneath. Autism is probably many different disorders (maybe some with more ADHD qualities than others), which is why kids with autism are a hugely diverse group. The exciting part of research, however, is that finding the genetic markers and brain pathways they control will eventually help us target better treatments. But in the meantime, we’re also getting a clearer picture, beyond the labels, of exactly what our kids are struggling with and how to help them.