Autism spectrum disorder (ASD), or just autism, is a neurological and developmental condition that affects social interaction, communication, learning, and behavior. It encompasses a range of conditions related to brain development.

In about 2 percent to 4 percent of cases, rare gene mutations or chromosomal abnormalities are a direct cause, as with ADNP syndrome, also known as Helsmoortel-Van der Aa syndrome (HVDAS). Some other genes whose rare mutations are associated with autism include ARID1B, ASH1L, CHD2, CHD8, DYRK1A, POGZ, SHANK3, and SYNGAP1. Many ASD-associated genes play roles in brain development or regulate other genes or proteins.

In 2013, all autism subtype diagnoses were merged into the broader diagnosis of ASD under the DSM-5, now updated as the DSM-5-TR. Currently, signs and symptoms are viewed on a continuum of autistic traits.

ASD is diagnosed clinically using the DSM-5-TR criteria. The diagnosis requires evidence of difficulties with social interaction and communication, along with at least two restricted, repetitive, or stereotyped behaviors or interests, as mentioned in the symptoms section.

Women and girls with autism, especially those without intellectual disabilities or language delays, often face challenges in getting diagnosed due to subtler symptoms. Girls are, on average, diagnosed at age 5.6, compared to 4.8 for boys.

Autistic children aged 3 to 5 who qualify are entitled to free preschool services offered through local school districts or learning centers. They may include therapy and learning assistance at home or in a classroom. If a child qualifies, an individualized education program (IEP) is created, outlining learning, behavioral, social, and self-care goals. Special education services are available until the child turns 21. At age 6, a reassessment is conducted to determine if the child still requires an IEP.

Some autistic children may benefit from a gluten-free or casein-free diet. Gluten is found in wheat, rye, and barley, while casein is present in dairy products such as milk and cheese. However, a gluten-free, casein-free diet may not work for everyone.