From the Guidelines

Autism Spectrum Disorder (ASD) is primarily caused by a combination of genetic and environmental factors.

Genetic mutations: Rare mutations with large effect, such as those in the PTEN gene, have been identified as risk factors for ASD 1.
Family history: Individuals with a family history of ASD are at higher risk of developing the disorder, with recurrence risks ranging from 2-10% for full siblings 1.
Genetic testing: Chromosomal microarray analysis and other genetic tests are recommended for all suspected cases of ASD to identify underlying genetic causes 1.

Environmental chemicals: Exposure to environmental chemicals, such as pesticides, heavy metals, and endocrine disruptors, has been linked to an increased risk of ASD 1.
Prenatal and early postnatal exposure: The early developmental period, particularly the prenatal period, is a sensitive time when the developing brain is susceptible to disruptions from environmental chemicals 1.

Gene-environment interactions: The relationship between genetic and environmental factors is complex, and it is likely that genetic mutations can increase susceptibility to environmental toxins, which in turn contribute to the development of ASD 1.

From the Research

Genetic variations, including inheritable and de novo gene variations, contribute to the development of ASD 2
Hundreds of genes have been identified that contribute to the deficits in communication, social cognition, and behavior associated with ASD, accounting for 10-20% of cases 2, 3, 4
Genetic modifiers, such as copy number variation, single nucleotide polymorphisms, and epigenetic alterations, play a key role in modulating the phenotypic spectrum of ASD patients 2, 3, 5

Parental perspectives on the causes of ASD in their children include genetic influences, perinatal factors, diet, prenatal factors, and vaccines 6
Environmental factors, such as epigenetic mechanisms, interact with genetic factors to contribute to the development of ASD 3, 5
Other factors, such as haploinsufficiency and protein-disrupting single-nucleotide variants, have also been identified as potential causes of ASD 3

ASD is a complex neurodevelopmental disorder with multiple causes, including genetic, environmental, and epigenetic factors 2, 6, 3, 5, 4
The causes of ASD are highly heterogeneous, and patients with similar pathogenic variants may be diagnosed on different levels of the spectrum 2, 4
Further understanding of the mechanisms underlying ASD is crucial for developing novel therapies and improving patient outcomes 2, 3, 4