There are both genetic and non-genetic influences along with environmental factors that are thought to be involved in the development of autism, but, none of them is clearly understood.
To review the incidence of Autism in 2018: 1:59 in the US (CDC) and 1:66 in Canada (Autism Speaks).
-if you have one child with ASD, there is a 2-18% chance of having a second child affected.
-among twins, studies have shown the there is a 36-95% chance that both will be affected.
-1.5% of children in the general population are affected (National Institute of Health, May 2020)
and 3.5% for children whose parents have a sib with Autism... if the mother has a sib who is affected, it is not significantly more likely to have an ASD affected child. But if the father
has a sib with Autism, it is significantly more likely.
-there is a 3x greater prevalence for males to be affected and reasons are unknown.
-Autism can change with age and can improve. 30% of young children have less severe symptoms at 6 years of age than at 3.
-many with Autism and ASD are able to live relatively normal lives. Most teens and adults show improvement overtime. Many remain stable and some get worse.
-there are known gene changes associated with ASD and people with these gene changes are at increased risk of developing the condition.
-a large study in 2019 involving 2 million people across 5 countries finds that ASD is 80% reliant
on inherited genes. Therefore environmental causes are responsible for just 20% of the risk.
At least 30% of these genes that increase risk are spontaneous ne novo mutations....meaning
that they mutate in the individual sperm or egg for no known reason.
I found it fascinating that in our pediatric practice in Roswell, NM, with a population of about 15000 patients, we had a very low incidence of Autism overall in the first decade of this century. About 70-75 % of our practice was Hispanic. At that time the non-Hispanic whites had a much higher incidence than Hispanics or Blacks. However this is rapidly changing. The 1 in 59 rate in the general US population in 2018 was an overall 15% increase from the previous 2 years, largely due to better outreach and diagnosis in the minority populations. But minority rates are now exceeding white rates, especially among Blacks, and Hispanics are paralleling Whites, implying that there are differences in risk factors (either greater exposure to environmental influences, or perhaps another trigger.). I'll have to follow this one.