Genetics By Far The Biggest Factor In Autism Risk, Study Says

(Photo: dusanpetkovic via Getty Images)

For decades, researchers and parents have searched for clues about what causes autism spectrum disorder (ASD), which now affects about 1 out of every 59 children in the United States. 

Now, a sweeping new study looking at more than 2 million people from five countries (Denmark, Finland, Sweden, Israel and Australia) found that about 80% of an individual’s risk of developing autism comes from inherited genetic factors and not from “environmental” influences, meaning anything other than changes to a gene’s DNA. 

“Everywhere we looked, in five different samples, what we saw was that genetic factors were most important,” study author Sven Sandin, a statistician and epidemiologist with the Karolinska Institutet in Sweden, told HuffPost in an email. 

That might sound surprising to mothers and fathers who for years have read story after story emphasizing possible risk factors from air pollution to the overwhelmingly discredited (but enduring) vaccine hypothesis. And indeed, experts say the media and public have been disproportionately focused on the role of modifiable contributors to autism, when genetics are the major driving force.

Here’s what parents need to know.

Genes are the biggest risk factor, but there are still lots of questions about which ones. 

In the new study, published in JAMA Psychiatry on Wednesday, Sandin and his co-authors used models to analyze population data from five countries that included more than 2 million people, more than 22,000 of whom had been diagnosed with autism. Looking at outcomes among family members and weighing them against factors such as shared environments and their specific genetic connections led to their conclusion that inherited genes account for about 80% of the risk of autism in children with the disorder.

That’s pretty much in line with similar recent studies that have suggested genes are the major contributing factor to ASD. What’s notable about this new investigation, however, is its sheer size. 

“What’s immense about this study is the number of children across the world that were [included] — two million in the study population — and the large span of time, of a 16-year follow-up,” Dr. Wendy Sue Swanson, a pediatrician with Seattle Children’s who did not work on the study, told HuffPost. “It’s hard to argue with the kind of tonnage of that number.”

Of course, researchers have known for decades that genetics contribute to ASD. But now that they are grappling with just how significant a factor heredity is, there’s mounting pressure to determine which specific genes contribute in which specific ways.

And for now, that’s largely a question mark. 

“There is a lot of work that still needs to be done,” Sandin told HuffPost. “We still do not know which specific genes contribute to risk. Also, there are numerous potential environmental factors that could be related to ASD either directly or acting together with genes. We have, so far, only been scratching the surface.”

That doesn’t mean modifiable factors don’t have an impact. 

“If I were going to walk away after reading this study and talk to a family ... I’d say, ‘OK, we still don’t know the other 20%. It’s fairly controversial, what makes up the modifiable part,’” Swanson said. 

Although they’re often called “environmental” influences in the scientific literature, these factors go beyond things like the potential impact of chemical exposures on a person’s likelihood of developing autism. Researchers are probing the possible role that everything from diet to infection during pregnancy might play. For now, the studies are ongoing. There just is not much that autism researchers and pediatricians can say in the way of, “If you avoid XYZ, you will decrease your child’s risk of developing autism.”

In an editorial that accompanied the new study, a team of three autism and psychiatry experts said the media has focused disproportionately on those environmental factors, perhaps because they are modifiable. An understandable pull exists to focus on the things that parents might be able to control to a certain extent. But that may have contributed to an incorrectly skewed sense of how much nature versus nurture contributes to the autism risk. 

“Where we’ve gone awry is pointing fingers at things that don’t cause autism,” Swanson said. “Look at where we are right now with measles, mumps, and rubella vaccine trust and look at where we are with outbreaks because there was erroneous, falsified, misinformation that for decades led parents to believe vaccines were causing autism spectrum disorders.”

Being aware of family risk can help with early intervention. 

Expectant parents who know they have some family history of autism might want to consider speaking with a genetic counselor if they have concerns, Swanson said. 

Being aware of family history and how it might contribute to a child’s autism risk also can help parents and pediatricians be mindful of early signs of autism as they arise. Research clearly shows that early interventions, which can begin as early as age 2, can help improve physical, emotional, and communication skills. 

“On some level, I feel like we should feel comforted by [these findings]. Because it’s almost like autism is explained ... it’s not because of what a parent is doing right or wrong,” Swanson said. “It is largely based on a child’s genetic makeup.”

Also on HuffPost

"This is what autism looks like in our home. This is Lucas, and he's 7. He was diagnosed in December 2016. He's considered high-functioning autistic. We took this photo to share his diagnosis with family and friends on Facebook. He is the light of our lives. He loves sports, loves school, and wishes to be a pilot when he grows up. Our silky terrier Bo is his 'baby brother.'"
"Zoe was diagnosed with autism at 23 months old. We had known for a long time prior to the testing that she had autism, but who was to say she wasn't just different than the rest. Every day is unpredictable. Zoe never has a boring day. I remember waiting YEARS to hear her first word. When she said it, I pulled the car over and cried so hard. She flapped her arms and did her self-stimming tongue thrusting, and I joined in too! She is just like every other child. She has good days and bad days. She has milestones and regressions. It's just that autism gives her that extra push to do things on a larger scale. I think she has started to learn that she is different than her classmates, and she has already been the target of bullying. Autism prevents her from understanding that bullies are trying to hurt her. She still will walk up to them and slowly make eye contact, smile, stick her hand out, say 'Hi friend! I'm Zoe Grace!', lick their cheek and skip away. #DifferentNotLess"
"My son (with glasses) and his twin brother. His brother has autism. They were raised apart but have recently been brought back together when we adopted our son. He sees his twin often now and cherishes their times. When his brother isn't understood by anyone else, my son can help others understand what his twin cannot express for himself. The face of autism in our house is the glow of brotherly love."
"Autism in our house is a big brother teaching little brothers his heavy work moves that they now do it together. Lego pieces as far as the eye can see but don't you dare touch them. Pokémon cards as far as the eye can see but don't you dare touch them. It's limited hugs and 'I love you's, but when they happen, they're special. It's worrying about the future and working at life skills every day, so he can be independent when the time comes. Celebration over little victories like new environments and people without a meltdown. Talking calmly through the meltdown, letting him know I'm here. Hurt feelings when friends/family/teachers don't understand behaviors and think he's misbehaved. Being a strong advocate in those situations when it would be easier to be angry at those who believe it's misbehavior. It's loving every minute I have with him and his brothers knowing we are doing the best we can."
"Autism is our family is new. My 2-and-a-half-year-old has been recently diagnosed. It is raising a beautiful bright strong-willed child who may have challenges, but we will learn and grow each day. She hasn't talked yet and has difficulty at preschool. And it's extra hard for us since it's just me and her, and I work full-time and go to school full-time. Between early intervention and family, we are thriving. She may be young but she has the kindest heart that is full of laughter. I am so proud of her every day."
"This is autism in our family. Can you tell which one is on the spectrum? Most people wouldn't guess, being that it's a picture. But, from left to right we have Maxwell who is 6, Gavin who is 8 and Bailey who is 2. Our middle child Maxwell was diagnosed on he autism spectrum at age 4. He's on the more severe end, being non-verbal and having sensory processing disorder. But, although he doesn't communicate, his siblings know when he's happy, sad, agitated, or just plain silly. We are very open and supportive in our household and try to give him as much opportunity as his two other siblings. The most important thing to us is to raise all three of our children to know that they are each other's support system, and family is first, always. We're autism advocates, but firstly, Maxwell advocates."
"Autism in our household is many things. It's unconditional love, it's long emotional days, but most importantly it's accepting different instead of ignoring and pretending it doesn't exist. Autism is everything awesome and exhausting, but there's nothing I would change about my son Michael."
"Autism to us and for us has been: screaming, laughing, tantrums, tickling, trying to balance autism and typical, biting (not love nips, the kind that cause permanent damage), hugging, smearing (if you don't know, you don't want to), singing, aggression/violence, the Muppets, Wiggles, Oobi and Sesame on constant repeat, hitting, music, crying, making silly faces, depression, innocence, mania, medications, frustration, holidays whenever the mood strikes, sleep disorder, fear, guilt, joy, loss, drums and guitars (real and created), grief, spontaneous hugs and kisses, injuries, destruction, creativity, sensory seeking/avoidance, limited speech, obsessions, packing a bag of supplies for outings when your child is 17, snuggling at bedtime to 'talk' about the day, always being on hyper-alert status, never cooking just one meal, celebrating and appreciating all victories and accomplishments, loss of friends and family, learning who your true friends are (who are now family), constant advocating, endless fighting for services/help, limited ability to do things together, trying to enjoy the few things we can do together, the Dollar Tree being our own personal 'Cheers' ... everybody knows her name, meltdowns (different from tantrums), childlike excitement vs. teenager angst, constant noise, anger and love."
"This is what autism looks like in our family. This is my 2-year-old, Noah. He was recently diagnosed with autism only about a week ago. He doesn't talk yet but is trying each day. He loves to line things up. It could be pens, army men, straws, teddy bears, anything. He loves music. He loves to dance, and he gets so excited, he flaps his hands. He can be mean to his siblings at times, but they are all learning different ways to distract him when he gets upset. Noah is so loved in our family. We wouldn't be our family without him!"
"Autism is what makes it extremely difficult for my son to communicate with others, it's what makes him unaware of social norms and how to form meaningful relationships with peers. Autism is trading guitar practice or T-ball practice for speech therapy, occupational therapy and ABA therapy. Autism also looks like the pure joy on his face when he is swinging, it's the confident smile he gets when communicating with his AAC device. Autism in our family teaches us to celebrate and appreciate every. single. thing. Autism is hard, but this face is tenacious, and because of that, so are we."
"My oldest daughter is in middle school. Not only does she play viola in school orchestra, she is a figure skater who would skate every day if she could. She is my little caretaker, and is always worried about how we are feeling. My son was non-verbal until the age of 7; once words finally started flowing (as opposed to just random sounds), his vocabulary has grown by leaps and bounds. He is on grade-level with his coursework and is an electronics whiz. His tablet is his most prized possession; he video records himself playing drums, or makes movies out of his favorite clips.
My youngest daughter puts the 'Autistic people are anti-social' notion to rest. She loves people, greeting everyone with an enthusiastic, 'Hi!' She makes eye contact and will sing and dance for you all day. The larger the audience, the better. She also loves to be silly and make you laugh. I never put a limit on what my children could do. Society does that enough already." 
"In my house, autism is being able to remember and recite a movie she's only seen twice, but not being able to remember her morning routine without a list or chart. Most importantly, though, my girl (who is 15) is absolutely accepting of all people who cross her path and does not see herself as different in any way. In my house, autism is being able to do whatever your peers do, but maybe do it in a different way or a different time frame."
"We have a vibrant, fearless non-verbal 3-year-old who is the apple of our eye. Liam was diagnosed in August 2016 and is now enrolled in an early education program that promotes inclusion. Nothing holds him back. We enrolled Liam in a Pre-CanSkate class at the local arena, and he rocked it so much so that he is going for another session this spring! While it's not the path we originally thought we would be traveling down, we definitely have a good tour guide!"
"What does Autism look like? It's this sweet little boy. We have so many struggles, but nothing brightens my day more than hearing his belly laugh when he's playing with his puppy or getting tickled by mom or dad or when his big brother chases him. I often think what my life would be like with two typical developing children. As dreamy as that sounds, without Patrick I would be a horribly judgmental person. I would think that my 'perfect' children were the result of all the perfect parenting decisions I had made. Patrick has taught me patience, understanding, acceptance and unconditional love that I would never really know without living with autism in our lives every single day."
"A diagnosis is simply a diagnosis and nothing more. It does not define who your child is. Autism or ASD (autism spectrum disorder) is a spectrum disorder that includes a large range of linked conditions. Autism doesn't come with a manual. It comes with a parent who never gives up. Alivia has taught me more about life in the last two-and-a-half years she's been here, than I could have ever imagined. She has taught me to be brave, to be strong, to be courageous. She has taught me that even when you're tired and feel like you are at a standstill, you can keep going. She has taught me that there are many other ways of communication than simply just speaking. She has shown me how incredibly exciting viewing the world from a different angle can be! On some days we struggle. We struggle a lot. And on other days we accomplish and overcome a lot. Every day is unpredictable, but on days where I can't seem to keep away the tears, I have to remember that there is a greater plan. God knew exactly what he was doing when he chose me to be Alivia's mom. He knew I would be able to be her voice. He knew I would never, ever give up, no matter what it will take. And just like all parents, we have many worries. I worry about many things. About her knowing how loved she is, about her future, about her going to school, about people being mean to her, about people knowing she's different, and just about her life in general. But I have to remember worrying won't get us anywhere right now. What is meant to be, will always be. If you ever met our Alivia, you know when you watch her or interact with her, she is just so very special, and I just hope the world can see her the same. I hope the world can learn she is different, not less. She lights my world brighter than the sunshine, and fills my heart with so much love. And I just hope when she goes to sleep every night, she can drift off to sleep knowing the same amount of sunshine in her life and love in her heart. Most of the time I don't find autism to be the struggle, I find other people's understanding of autism to be the struggle."
"In our house, autism looks like utterly adorable and funny and sweet quirks from this kid right here. He is like a combination of Brick from 'The Middle' and Dewey from 'Malcolm in the Middle,' and as the middle child in a rather large brood, he brings out a level of tenderness in all of us that makes this family as amazing as it is. I wouldn't change him for the world."
"Autism in our family means that love needs no words, nor does it have any boundaries. Our Alex changes the world with his smile and his unbridled joy without ever speaking a word. I knew at 3 months that something was amiss with my first sweet baby boy. At 13 months a diagnosis and at 8 years old, his mom graduated with a master's degree in applied behavior analysis and autism. Autism has changed my life in every way, and I am so much better for it. I have witnessed the smallest miracles that others take for granted. I have heard my son speak after years of speech therapy and then lost it. I have celebrated my son learning to use an iPad to tell me what he wants for snack after years of frustration. I have learned with my son and celebrated every step of the way. To love a child with autism is to live with an aching grief that few understand. It is also the most unbelievable joy, those milestones, goals and dreams achieved. Our end of the spectrum is a difficult path. We focus on functional goals rather then academic, as college or even standardized testing are no longer dreams. We focus on the things that matter, and we work on them and celebrate them and make sure to always work on them so they last. Our dreams have changed but they are still beautiful. We have two younger boys who are empathetic, sweet and kind in a way that is only possible because Alex is their brother. They look for the kid playing alone and make sure to say hi. They are kind and patient with their brother and quick to defend him when there are too many stares or whispers in public. Autism has made us all better people. Autism colors our world and makes everything more vivid and clear. I wish we could move past being aware to being accepting and inclusive."
"Autism in our house is finding those moments that will bring joy to our son's face. Finding the moments that he's not too anxious, so we can hug him. Finding the moments to sit with him, so he can fill our minds with his immense knowledge. Finding moments where he's concentrating on something so dear to him, and I stare at him and can't believe that he's ours. I wouldn't change him or any of his quirks for the world."
"My son Connor is 5 years old. At 3, he was completely non-verbal. He finally said 'Mommy' at 3-and-a-half. It was one of his first words and made me cry happy tears. He is now verbal and ready to start kindergarten in the fall. All of our hard work is showing, and we are so proud of him."
"Our daughter has Down syndrome and autism. For us, autism looks like a lot of things. Sometimes loneliness, sometimes happiness, sometimes confusion, sometimes overwhelmed. Always love. There's always love."
"Autism looks like love and sadness. Hope and heartache. Beauty, magic, persistence and turmoil. It looks like a little boy that loves collecting DVDs so much that he asks for a DVD cake every year. We are challenged, but we are blessed."
"My daughter is 7 -- diagnosed at age 2.5. As scary as it was, getting a diagnosis so early was the blessing. She did six hours of therapy a week for two years. It was tough, but she made tons of progress. She is in a mainstream classroom with support and progressing well. The rule in our house is that you never apologize for who you are."
"This is what autism looks like in my house. My son was diagnosed at 18 months. He always spoke but is not a great communicator. He is loving, highly empathetic, engaging, intelligent and friendly to a fault. But he struggles with debilitating anxiety and rage. His focus is severely impacted, he has sensory challenges and goes through food phases where he wants to eat the same thing for months at a time. He is incredibly scared to be alone, at any time, even for a few seconds. He always seems to latch on to old or hard-to-find shows and movies, as is shown in the photo -- 'CatDog,' 'Roger Rabbit,' and 'Three Caballeros' toys he received for Christmas. To his core all he really wants is love, friendship and acceptance."
"Autism in our family is coming full circle, it is looking back on the very early years and wondering how you did it all. It is raising a non-verbal son with significant needs all while trying to balance life with his neurotypical sister. Autism in our house is facing the empty nest after 22 years of caregiving. It is navigating the system after 18 and ensuring that once we are gone, our son has a safe and happy home. Autism in our family is realizing that you will never stop wishing that you were a millionaire so that you could make sure your child will be taken care of the way you want once you are gone. And autism in our house is realizing no matter how tough it gets, the love and strength of your family is tougher!"
"Every day in our home is #AutismAwareness thanks to this little blue-eyed miracle child that I have the pleasure and honor of calling my son. This is Joseph. He was diagnosed with PDD-NOS at 18 months old. It was later changed to moderate autism. This boy, whose smile shines brightly with love and laughter. My little man, whose heart is so kind and compassionate and who genuinely just wants everyone to be happy. He is beyond intelligent, witty and wise beyond comprehension. He works so hard on a daily basis learning to deal with social protocols and changes in routine. I'm exceedingly proud of our Joseph for his fortitude and tenacity, his generous soul and protective nature over his little brother. He keeps us on our toes, but I wouldn't have it any other way."
"What autism looks like to me: My baby. My world. Making me proud every day. He may never get the chance to tell me in words how he feels or how his day was. But I will understand him regardless, and I will help him understand the world."
"Autism in our house is constant conversations about Minecraft and Skylanders. We are pretty proud of this photo. It was six years in the making. His last.hair cut at a salon was when he was 3 years old. He would go into meltdowns from the sensory overload of a haircut. In February 2017, he kept asking to dye his hair red, so we went back. He got a haircut and dye. He was so proud and so were we! He's 9 now, almost 10 and every day has its challenges, but every day I also see him persevere through uncomfortable sensory or social situations. He's come so far and we are beside him every step of the way!"
"This is my son Kameron. He is 8 years old, and he has two sisters. In our house, autism looks like happiness. He has a smile that is contagious and a love for life that is inspiring! We think he is fabulous. We say all the time that he isn't autistic; he has autism!"
"Two of my sons -- my eldest Mariono and my youngest Xavi -- are autistic. Mariono was diagnosed at 7 with Asperger syndrome. Xavi was recently diagnosed."
"Both boys have been diagnosed with autism. Dominic is 4.5 and was diagnosed at 2, Ryder is 20 months and was diagnosed at 17 months. I, their mother, am also on the spectrum, and I have a variety of other mental health problems."
"Shane was diagnosed with autism at 15 months of age. It took my insistence to the pediatrician that something was wrong. I finally got the referral at nine months and waited six months to get into a developmental pediatrician. Shane was not a typical baby. He didn't want to be held, cried inconsolably, no eye contact, no words. I even had to put him in a bouncer seat to feed a bottle to him. He did just enough babbling of sounds to make the doctor believe he was fine, but I knew he wasn't. Sometimes as a mom you have to trust your gut and go against what the doctors and everyone else tells you. You are the mom, and you know your child. Never doubt your intuition. When we got the diagnosis at 15 months of age, I asked for another referral to get a second opinion, and it was confirmed by another doctor. When we returned to our pediatrician with a diagnosis, he said, 'Now I can see it, but I wasn't so sure in a child so young.' It is hard for a doctor to determine in a short office visit. Don't wait for a doctor to tell you, seek out your own answers. There was a time when we sat in the waiting room of an emergency department saying that we wouldn't leave until we got answers. Do what you need to do. Doctors see a small piece of the puzzle, while you see the whole picture."
"This is what autism looks like to us. Riley. He has a gentleness about him, sensitive, and funny, but will be moody and rage at the slightest routine change. They are focusing a lot about the transition into middle school, & it's triggered his OCD/anxiety. After his bald spot grows in we're going to keep his hair short. I'm sure it will help his hair situation, but he'll go back to chewing his fingers until they bleed, or ripping papers into a million pieces. I still haven't figured out how to not step in and speak for him in social situations. Many times, I'm torn between making him do something I know he's uncomfortable with vs. letting him stay home in his safety zone. I refer to Riley being like a light switch: If he's on, we're good, but if he's off, forget about it. I don't care what homework is incomplete, we're done. I love my son."
"Autism is learning to have lots of patience in a world that has very little! Autism is stressful, lonely and expensive! Autism is obsessions, scripting, routines and meltdowns! This is Ethan; he has an infectious smile, gives the best hugs ever, and can tell stories with just his eyes! He also struggles every single day to do the things others might take for granted! Autism is definitely hard for him, but he's such a happy boy for the most part!"
"Autism in our house is screams and desperate cry and meltdowns sometimes. But also hugs and kisses and songs and drawings and love and cupcakes and Legos and inventions and extreme purity of heart"
"Lacey and I were diagnosed with ADHD in 2018, and Lacey was officially diagnosed with autism in March 2019. (After Lacey's diagnosis, I also self-identify as being autistic.) After Lacey's diagnosis, we realized autism was an undiagnosed condition in multiple generations of my family on my mother's side. I am single mom to two beautifully wild children, and own a business helping families in the Kitchener-Waterloo area enjoy a well deserved break at my family-focused wellness centre, Knead a Break Kitchener. Our home is filled with love and hilariously beautiful chaos."

Love HuffPost? Become a founding member of HuffPost Plus today.

This article originally appeared on HuffPost.