Researchers believe there are many associations with parental age at the time of conception and its deleterious effects on children’s health. Studies have shown advancing paternal and maternal age were both associated with poor pregnancy outcomes.
In one study, fathers over 50 years of age had a 66% higher chance of having a child with autism. This same study also found mothers over age 40 and under age 20 increased the risk of autism. A second study shows father’s over age 45 at time of conception, when compared with fathers between 20-24 yrs. of age, had a heightened chance of having offspring with autism, ADHD, bipolar disorder, and other psychiatric and academic morbidities. The effects of advanced paternal age on semen quality are controversial. However, the literature strongly points to issues with spermatogenesis, specifically epigenetic changes, and DNA mutations associated with increased paternal age.
Women, born with a set number of eggs, may be more susceptible to de novo mutations when an older egg is fertilized. These first time mutations are believed to be influenced by epigenetic changes affecting DNA replication, thereby increasing the rate of autism and other chronic health issues in the offspring. Epigenetic alterations associated with age can result from long-term exposures to environmental toxins, substance abuse, prescription medication usage, and diet. While younger moms have had less exposure to environmental toxins, researchers speculate their associated risk may be related to immature reproductive systems. Researchers also suggest disparity of more than 10 years between parents’ ages has also been shown to increase the risk of autism, although the mechanism is unknown.
There is contradictory evidence to support to what extent the age of the parents affects the health outcomes of their children. For example, a study published in Evolution, Medicine and Public Health, found that while children of older parents are more likely to have autism, they are not more likely to have other neurological disorders such as schizophrenia. However, another study by Nature Genetics, finds older fathers have a higher risk of psychiatric disorders like schizophrenia. Furthermore, many studies draw contradictory conclusions as to which age brackets pose the highest risk for poor health outcomes of children. Ultimately, researchers believe there are underlying reasons as to why older parents are more likely to have children with autism, however, the exact mechanisms are unknown.