Tuesday, August 4, 2020
US flag

Autism risk increases with parents’ age

A new study published in Evolution, Medicine, and Public Health indicates that parents who reproduce later in life are more likely to have children who develop autism disorders. Later reproduction was not, however, associated with increased risk for schizophrenia in offspring.

Multiple studies on this subject for over 30 years have found that risk patterns for these disorders are highly variable and often remain incomparable between public health studies due to substantial differences in study design. Now researchers from the Copenhagen Centre for Social Evolution have analyzed a massive single population sample from Denmark to compare risks based on maternal and paternal age, and parental age difference.

The authors used a sample of about 1.7 million Danish people born between January 1978 and January 2009, out of which approximately 6.5% were diagnosed with autistic or schizophrenic disorders during this time. Their data included the full spectrum of nation-wide autistic and schizophrenic diagnoses for up to 30 years of age and over twenty potentially confounding medical and socio-economic factors that they could statistically control for.

Unique personal identification numbers were used to link individuals’ information between different Danish health registries, including the National Patient Registry (holding nationwide hospital admissions since 1977) and the Psychiatric Central Register (with diagnoses for all inpatient admissions since 1969). Combining these data sets also provided the ages of parents when children were born.

Above-average paternal and maternal ages were associated with increased risk of most autistic disorders in offspring and this effect was magnified in offspring of very old fathers. However, advanced maternal and paternal ages were not associated with higher risk of any schizophrenic disorder. In contrast, children of young parents had reduced risks of autism and only children of very young mothers had increased risks of schizophrenia.

More dissimilarly aged parents meant enhanced risk for both autistic and schizophrenic disorders in offspring compared to parents with similar ages at childbirth, but only up to a certain point where risks leveled out. For example, higher risk for autism in offspring of older fathers (or mothers) would tend to be compensated if they had a child with a much younger partner.

“The magnitude of these increases and decreases in statistical risk need to be scaled against the fortunately rather modest absolute risks of being diagnosed with a mental disorder in Denmark, which is 3.7 percent for all autistic disorders and 2.8% for all schizophrenic disorders up to 30 years of age. The highest increases and decreases that we could relate to paternal and maternal age added only 0.2 to 1.8 percent to these absolute risks, but represented changes in relative risk of 76 to 104 percent,” says Dr Sean Byars, the first author of the study.

The study also discusses why these risk patterns continue to exist in modern humans and suggests that they are remnants of our evolutionary past. In an earlier study of the same population the authors showed that autism risks are associated with above average sizes at birth and schizophrenia risks with smaller (but) still normal sizes at birth. The authors highlight that modern families of one to three children now typically originate at ages that our ancestors were completing families of six to eight children provided these children survived.

“Natural selection has shaped how parents, and particularly mothers, allocated their reproductive investments best in the face of uncertain conditions during our prehistory and well into modern historical times,” said Professor Jacobus Boomsma, the senior author of the study. “It was not very long ago that most mothers had their first child around the age of 20 and went through 10 pregnancies. Our modern reproductive patterns are thus a poor match to what humans are likely to be naturally adapted to. Our evolutionary interpretations suggest how we can possibly understand recently increased mental disease risks that have no direct medical explanation.”

Paul Katula is the executive editor of the Voxitatis Research Foundation, which publishes this blog. For more information, see the About page.

Recent posts

Voxitatis congratulates the COVID Class of 2020

2020 is unique and, for high school graduates, different from anything they've seen. Proms, spring sports, & many graduation ceremonies are cancelled. Time for something new.

Vertical addition (m3.nbt.2) math practice

3rd grade, numbers and operations in base 10, 2, 3-digit vertical addition practice problem

Rubber ducks (m3.oa.1) math practice

3rd grade, operational and algebraic thinking, 1, rubber ducky modeling practice problem

Distance learning begins as Covid-19 thrives

What we learn during & from coronavirus, a challenging & imminent crisis, will provide insights into so many aspects of our lives.

Calif. h.s. choir sings with social distancing

Performances with the assistance of technology can spread inspiration across the globe even as the coronavirus spreads illness and disease.

Families plan to stay healthy during closures

Although schools are doing what they can to keep students learning and healthy during the coronavirus outbreak, that duty now shifts to parents.

Illinois temporarily closes all schools

IL schools will be closed on Tuesday, March 17, through at least March 30. Schools in 18 states are now closed due to coronavirus.

Coronavirus closures & cancellations

Many schools are closed and sports tournaments cancelled across America during what the president called a national emergency: coronavirus.

Coronavirus closes schools in Seattle

The coronavirus pandemic has caused colleges to cancel classes, and now Seattle Public Schools became the nation's first large district to cancel classes due to the virus.

Most detailed images ever of the sun

A new telescope at the National Solar Observatory snapped the most detailed pictures of the sun's surface we have ever seen.

Feds boost Bay funding

Restoration efforts in the Chesapeake Bay watershed received a boost in federal funding in the budget Congress passed last month.