ASD does not have a single cause. It is a disorder with many causes, where several of the factors associated with the disorder are still unknown.
Currently we know that there are genetic factors, which explain a greater incidence in certain families and a high matching between identical twins.
There are also environmental factors, which act as risk factors, leading to the emergence of the disorder. The advanced age of the parents, the ingestion of poisons and certain medicines during pregnancy (valproate), as well as a low weight at birth are factors that could be related with the appearance of ASD.
Therefore, the old psychological theories have been thrown out, which maintain that autism was associated with a cold or unempathetic relationship with the baby (refrigerator mother theory). A theory that produced feelings of guilt in fathers and mothers of children with ASD.
On the other hand, the prevalence of ASD, according to the DSM-5, is estimated to be around 1% of the population, affecting both the child and adult population, since the disorder affects the person throughout their entire life.
It affects men more often than women, at a ratio of 4 to 1.
The increase in affected persons both can be explained by improvements in diagnosis, which has caused new previously undiagnosed cases to surface, as well as a possible increase in the number of affected persons and changes in the diagnosis criteria of the DSM-5.