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Conflicting Pictures Emerge of Autism in Girls

Marina Sarris
Interactive Autism Network at Kennedy Krieger Institute
Date Published: 
May 20, 2016

Photo of girl with autism to illustrate article about sex differences in autism (iStock)Once called "research orphans"1 because no one studied them, girls have been a popular topic in autism research circles in recent years.

Girls and women make up only about 20 percent of people with autism, but some researchers wonder if their true numbers are larger. Do many simply elude diagnosis because their symptoms are different, or because they are good at "pretending to be normal," to quote one female author with autism?2 Do textbooks and diagnostic manuals describe "male autism" better than the female version? The answer is important because some girls may be slipping through the diagnostic cracks.3 Girls who fail to get diagnosed correctly may never receive the therapy or help in school that they may need.

A new study highlights just why it's so hard to pin down male-female differences in autism spectrum disorder (ASD).4 Researchers in Rhode Island and Massachusetts reviewed four research databases, which together include 5,700 males and females with autism. They wanted to see if there's a "female phenotype" of autism, that is, a particular way that autism looks in girls. "That question has gained a lot more attention in the last five years or so," explained lead researcher Yamini J. Howe, MD, now an Assistant in Pediatrics at Lurie Center for Autism/MassGeneral Hospital for Children in Massachusetts.

The results, however, were not straightforward. Dr. Howe's group found no differences between boys and girls with autism who do not speak. Both sexes performed similarly on tests of intelligence, social abilities, and daily living skills.4

Different results when focusing on girls who speak

But when they focused on girls and boys who have phrase or fluent speech, they got two very different pictures of how they compared to one another. People with phrase speech use simple utterances of up to three words, while fluent speakers use more complex sentences to communicate.5

Girls who took part in two of the autism research projects, the Simons Simplex Collection and the Autism Treatment Network, scored lower on tests of intelligence, social abilities, and daily living skills than the boys.4

But the opposite was true for girls in the other two projects, the Autism Genetics Resource Exchange and the Autism Consortium. They had similar or better abilities than the boys.4

So which is it? Do girls who speak have milder or more severe autism than boys with the same level of verbal ability?

Photo of autism researcher Dr. Yamini J. Howe, courtesy of Lurie Center/MassGeneral HospitalThe answer may have more to do with how studies select participants than sex differences, the researchers said. The Simons Simplex Collection is composed of families who only have one member with autism ("simplex" means one), while the other studies allowed or encouraged families with multiple members with autism to enroll. Do girls who are the only members of their families with autism have a different – or more severe – form of it? Or, looking at it another way, in families with several members with autism, are parents more likely to seek an autism evaluation for their daughters with mild symptoms? "If you already have an idea that autism is a risk in your family, are you more likely to notice more subtle symptoms of it?" Dr. Howe asked. Or, perhaps the cause of autism is different in families that have many members with it than in families who have just one.

The study does not answer those questions, but points out that one must consider who is included in a study before deciding whether the results apply to everyone. It's still possible that girls with "higher-functioning" autism may be eluding diagnosis, which makes it harder to draw conclusions about girls as a whole.4

Dr. Howe said she became interested in studying girls after noticing how many more boys than girls came to her clinic. With the girls she did meet, "I had a feeling that there was something more we could be offering them." Some did not fit neatly into an ASD label, using standardized testing, she noted. "What is the best way to advocate for the best services or treatments for these girls?" she wondered.

Her study recommends more research on sex differences in autism, particularly involving females who speak fluently.

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References: 
  1. Bazelon, E. (2007, August 5, 2007). What autistic girls are made of. The New York Times Retrieved from http://www.nytimes.com/2007/08/05/magazine/05autism...
  2. Willey, L. H. (1999). Pretending to be normal: Living with Asperger's syndrome. Philadelphia, PA: Jessica Kingsley Publishers.
  3. Dworzynski, K., Ronald, A., Bolton, P., & Happe, F. (2012). How different are girls and boys above and below the diagnostic threshold for autism spectrum disorders? Journal of the American Academy of Child and Adolescent Psychiatry, 51(8), 788-797. doi:10.1016/j.jaac.2012.05.018 [doi]
  4. Howe, Y. J., O'Rourke, J. A., Yatchmink, Y., Viscidi, E. W., Jones, R. N., & Morrow, E. M. (2015). Female autism phenotypes investigated at different levels of language and developmental abilities. Journal of Autism and Developmental Disorders, 45(11), 3537-3549. doi:10.1007/s10803-015-2501-y [doi]
  5. Kennedy Krieger Institute. (2013). Speech emerges in children on the autism spectrum with severe language delay at greater rate than previously thought. Retrieved from https://www.kennedykrieger.org/overview/news/speech...