5 Reasons Symptoms of High-Functioning Autism Can Be Missed

Autism spectrum disorder (ASD) is typically diagnosed in toddlerhood or early childhood, but it is possible for clinicians and parents to miss or overlook the symptoms of high-functioning autism (HFA), in particular, until late childhood, adolescence, or even adulthood.

Even when someone is diagnosed later than usual, their symptoms will have been present since they were very young. In fact, to qualify for an autism diagnosis, symptoms must have been present from early childhood. Here's why HFA symptoms can fly under the radar, sometimes for a long time.

Teenage girl talks to school counselor
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Masked Symptoms

People with HFA are usually of normal intelligence, and sometimes even exceptionally intelligent. These traits can mask certain symptoms. The ability to do well in school, communicate effectively, and pass an IQ test are impressive—and may send parents and teachers down the wrong path when looking for reasons for a child's unusual issues or behavior. Even pediatricians can miss signs of autism when a child is able to communicate intelligently using spoken language.

In some cases, kids' strengths carry them through early elementary school with only minor issues, but then they have more difficulty when schoolwork becomes more abstract, demanding, and verbal—and when social interactions become more complex. 

If the obvious external signs of autism are not present, making a diagnosis can be very challenging.

It's also possible that a person with HFA developed the means to hide, manage, or overcome their symptoms. If they are told often enough to make eye contact, stop rocking, or talking about the same topics too much, it's possible they were able to mask their overt symptoms.

Early Misdiagnoses

It's not uncommon for someone to have received another, related diagnosis while the underlying autism went undetected. Many people with autism also have diagnoses of attention-deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), social anxiety disorder (SAD), and other developmental or mental health disorders.

A child with another diagnosis may not be properly evaluated for autism until later in childhood or even into adulthood.

According to a 2019 study, 10.3% of adults with autism were incorrectly diagnosed with ADHD as children, while 12.1% of children initially diagnosed with ADHD were subsequently diagnosed with autism.

Age

Another explanation is that a person may have been born before high-functioning autism was included in the diagnostic literature.

There were plenty of kids with symptoms consistent with HFA before 1994, when Asperger's syndrome (a diagnosis used for HFA at the time)— was added to the fourth edition of the Diagnostic and Statistical Manual of Mental Health Disorders (DSM-IV). In 2013, when the fifth version of the Manual (DSM-5) came out, Asperger's was removed as a diagnosis and replaced with level 1 autism spectrum disorder.

Furthermore, these people may have received a diagnosis of something other than autism, as autism would have been considered too extreme a diagnosis for a high-functioning person at the time—and they may never have thought of seeking a new diagnosis as an adult.

Female Sex

Some research suggests that women and girls are under-diagnosed with autism. Four times as many boys and men are diagnosed with autism than women and girls, but the reasons are not clear. 

Are girls really less likely to be autistic? Or are their behaviors (apparent shyness, discomfort with public speaking, difficulties with motor coordination, confusion over social communication in situations such as team sports) considered "feminine" rather than problematic?

Or do girls with high-functioning autism actually behave differently from boys with autism, tending to be less aggressive, more imitative, and more likely to work hard to "fit in"? 

A 2015 study suggests that females are genetically "immune" to some of the symptoms of autism (a concept referred to as the "female protective effect"). The theory suggests that symptoms of autism manifest differently in women and girls and that females tend to demonstrate better functional social behavior compared to males with autism.

While the reasons are not well understood, it seems clear that being a a female on the autism spectrum may make you less likely to receive a diagnosis.

Income and Ethnicity

Those from poorer and/or minority backgrounds are often underdiagnosed with autism. There seem to be two major reasons for this disparity.

The first and most obvious is that people with less money have less access to behavioral health care—and so are less likely to receive services, particularly for a child who is not obviously autistic. This translates to lower rates of autism diagnoses as well as poorer outcomes for autistic children who are diagnosed.

The second reason seems to relate to cultural differences: In some communities, the behaviors associated with high-functioning autism are not considered to be particularly problematic. And, of course, for recent immigrants, it's not surprising to hear that their child is not fitting in perfectly with American cultural norms.

A Word From Verywell

If you think your child—or you—may be on the autism spectrum, your healthcare provider or a mental healthcare professional can give you information on how to be evaluated.

Many people who are diagnosed later in life may have had many challenges throughout their lives and struggled to find acceptance. Getting an official diagnosis can open the doors to understanding, therapies, and support that would not otherwise be available.

Frequently Asked Questions

  • What percentage of autism cases are undiagnosed?

    Research suggests that one in four people with autism are not diagnosed. Factors that make it more likely for the diagnosis to be missed include being of a race other than white and not having an intellectual disability.

  • What are signs of high functioning autism in adults?

    Signs of high functioning autism in adults include:

    • Anxiety over social situations
    • Appearing blunt, rude, or disinterested without meaning to 
    • Avoiding eye contact
    • Difficulty making friends
    • Difficulty understanding what others are thinking or feeling
    • Finding it hard to say how you feel 
    • Having a very keen interest in narrow subjects
    • Maintaining strict routines and being anxious if it changes
    • Not understanding social rules
    • Noticing small details, patterns, smells, or sounds that others do not
    • Preferring to be alone
    • Taking things literally
  • How is an adult diagnosed with autism?

    A neuropsychologist typically diagnoses autism. In adults, the Autism Diagnostic Observation Schedule, Second Edition (ADOS-2), Module 4, is used to diagnose autism. If you suspect you have autism, talk to your healthcare provider about getting a referral to a neuropsychologist. 

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