Autism spectrum disorder (ASD), or autism, is a broad term used to describe a group of neurodevelopmental conditions.

These conditions are characterized by differences in communication and social interaction. People with ASD often demonstrate restricted and repetitive interests or patterns of behavior.

ASD is found in people around the world, regardless of race and ethnicity, culture, or economic background.

According to the Centers for Disease Control and Prevention (CDC), ASD is diagnosed more often in boys than in girls. A study of 8-year-olds in 11 locations throughout the United States found a 4.3-to-1, boy-to-girl ratioTrusted Source in 2016. About 1 in 54 of the study participants had ASD.

There are indications that instances of autism are on the rise. Some attribute this increase to environmental factors. However, experts debate whether there’s an actual increase in cases or just more frequent diagnoses. Compare autism rates in different U.S. states.

Symptoms of ASD typically become clearly evident during early childhood, between ages 12 and 24 months. However, symptoms may also appear earlier or later.

Early symptoms may include a marked delay in language or social development.

The DSM-5 divides symptoms of ASD into two categories:

• problems with communication and social interaction
• restricted or repetitive patterns of behavior or activities

To be diagnosed with autism, a person must experience symptoms in both of these categories.

Problems with communication and social interaction

ASD can involve a range of issues with communication, many of which appear before age 5.

Here’s a general timeline of what this might look like:

• From birth: trouble maintaining eye contact
• By 9 months: not responding to their name
• By 9 months: not displaying facial expressions reflective of their emotions (like surprise or anger)
• By 12 months: not engaging in basic interactive games, like peek-a-boo or pat-a-cake
• By 12 months: not using (or only using a few) hand gestures, like hand-waving
• By 15 months: not sharing their interests with others (by showing someone a favorite toy, for example)
• By 18 months: not pointing or looking where others point
• By 24 months: not noticing when others appear sad or hurt
• By 30 months: not engaging in “pretend play,” like caring for a baby doll or playing with figurines
• By 60 months of age: not playing turn-taking games, like duck-duck goose

Additionally, autistic children might have trouble expressing their feelings or understanding those of others starting at 36 months.

As they age, they might have difficulty talking or very limited speaking skills. Other autistic children might develop language skills at an uneven pace. If there’s a particular topic that’s very interesting to them, for example, they might develop a very strong vocabulary for talking about that one topic. But they might have difficulty communicating about other things.

As autistic children begin talking, they might also talk in an unusual tone that can range from high-pitched and “sing-songy” to robotic or flat.

They might also show signs of hyperlexia, which involves reading beyond what’s expected of their age. Children on the autism spectrum might learn to read earlier than their neurotypical peers, sometimes as early as age 2. But they tend to not comprehend what they’re reading.

While hyperlexia does not always accompany autism, research suggests nearly 84 percent of children with hyperlexia are on the spectrum.

As they interact with others, autistic children might have difficulty sharing their emotions and interests with others or find it hard to maintain back-and-forth conversation. Nonverbal communication, like maintaining eye contact or body language, might also remain difficult.