Summary: A new study reports on the real risks of parental age and the links between autism and schizophrenia in the offspring.
Source: Oxford University Press USA.
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% 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 0.2-1.8% to these absolute risks, but represented changes in relative risk of 76-104%.”, 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 1-3 children now typically originate at ages that our ancestors were completing families of 6-8 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.”
Funding: Funding provided by Danish National Research Foundation, Marie Curie International Incoming Fellowship.
Source: Daniel Luzer – Oxford University Press USA
Image Source: This NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Opposite differential risks for autism and schizophrenia based on maternal age, paternal age, and parental age differences” by Sean G. Byars and Jacobus J. Boomsma in Evolution Medicine and Public Health. Published online July 26 2016 doi:10.1093/emph/eow023
[cbtabs][cbtab title=”MLA”]Oxford University Press USA. “Is There a Real Connection Between Parent’s Age and Risk for Autism and Schizophrenia?.” NeuroscienceNews. NeuroscienceNews, 3 October 2016.
<https://neurosciencenews.com/parental-age-autism-5185/>.[/cbtab][cbtab title=”APA”]Oxford University Press USA. (2016, October 3). Is There a Real Connection Between Parent’s Age and Risk for Autism and Schizophrenia?. NeuroscienceNews. Retrieved October 3, 2016 from https://neurosciencenews.com/parental-age-autism-5185/[/cbtab][cbtab title=”Chicago”]Oxford University Press USA. “Is There a Real Connection Between Parent’s Age and Risk for Autism and Schizophrenia?.” https://neurosciencenews.com/parental-age-autism-5185/ (accessed October 3, 2016).[/cbtab][/cbtabs]
Abstract
Opposite differential risks for autism and schizophrenia based on maternal age, paternal age, and parental age differences
Background and objectives: Effects of maternal and paternal age on offspring autism and schizophrenia risks have been studied for over three decades, but inconsistent risks have often been found, precluding well-informed speculation on why these age-related risks might exist.
Methodology: To help clarify this situation we analysed a massive single population sample from Denmark including the full spectrum of autistic and schizophrenic disorders (eliminating between-study confounding), used up to 30 follow-up years, controlled for over 20 potentially confounding factors and interpret the ultimate causation of the observed risk patterns using generally accepted principles of parent-offspring conflict and life-history theory.
Results: We evaluated the effects of paternal age, maternal age and parental age difference on offspring mental disorders and found consistently similar risk patterns for related disorders and markedly different patterns between autistic and schizophrenic disorders. Older fathers and mothers both conferred increased risk for autistic but not schizophrenic disorders, but autism risk was reduced in younger parents and offspring of younger mothers had increased risk for many schizophrenic disorders. Risk for most disorders also increased when parents were more dissimilarly aged. Monotonically increasing autism risk is consistent with mutation accumulation as fathers’ age, but this explanation is invalid for schizophrenic disorders, which were not related to paternal age and were negatively correlated with maternal age.
Conclusions and implications: We propose that the observed maternally induced risk patterns ultimately reflect a shifting ancestral life-history trade-off between current and future reproduction, mediated by an initially high but subsequently decreasing tendency to constrain foetal provisioning as women proceed from first to final pregnancy.
“Opposite differential risks for autism and schizophrenia based on maternal age, paternal age, and parental age differences” by Sean G. Byars and Jacobus J. Boomsma in Evolution Medicine and Public Health. Published online July 26 2016 doi:10.1093/emph/eow023
