Causes of autism

The causes of autism are a subject of scientific research, but understanding of the etiology of autism is incomplete. It is influenced by a complex interplay of genetic, epigenetic, prenatal, perinatal, and environmental factors. Genetics play a major role, with heritability estimates ranging from 60–90%. De novo mutations—including copy number variations and gene-disrupting mutations—contribute to approximately 30–40% of cases. However, most autism cases involve complex interactions among multiple inherited genetic variants, many of which are still unknown.

Epigenetic mechanisms, such as DNA methylation and genomic imprinting, also influence gene expression and susceptibility, often interacting with environmental exposures. In rare cases, autism has been associated with agents that cause birth defects.

Prenatal risk factors include advanced parental age, maternal metabolic or autoimmune disorders, infections, and prenatal stress, while perinatal risks involve preterm birth, low birth weight, and birth complications. Postnatal mechanisms have been proposed, including immune dysregulation, gastrointestinal abnormalities, oxidative stress, and neural circuit differences, though these remain largely unproven and are the focus of ongoing research. Some Neanderthal-derived genetic variants may influence susceptibility. Current high-quality evidence shows no causal link between prenatal use of paracetamol and autism.

Overwhelming scientific evidence shows no causal association between thiomersal and vaccines, including the measles-mumps-rubella (MMR) vaccine, and autism. Parental concern about vaccines has led to a decreasing uptake of childhood immunizations and an increasing likelihood of measles outbreaks. The refrigerator mother theory has been conclusively refuted by scientific evidence.