If the father is obese, are his children at risk of autism and other developmental disorders?
On the surface, it doesn't sound likely. Several studies have previously looked at the role of maternal obesity but now, Norwegian researchers say they have found that paternal obesity could be an even greater risk factor -- but caution that much more must be learned.
“We have a long way to go. We must study genetic factors in the relationship between obesity and autism, as well as environmental factors associated with switching the genes on or off - so-called epigenetic factors,” said Dr. Pål Surén of the Norwegian Institute of Public Health.
Surén and his fellow researchers used data from the Norwegian Mother and Child Cohort Study (MoBa). The researchers studied questionnaire data from over 90,000 Norwegian children at 3, 5 and 7 years of age.
The mothers had answered detailed questions about their own mental and physical health, and about their children. The fathers completed a questionnaire about their mental and physical health while their partner was pregnant.
Of the sample, 419 children, approximately 0.45%, had an autism spectrum diagnosis (ASD).
In the sample, 22% of the mothers and 43% of the fathers were overweight, with a body mass index (BMI) of between 25 and 30. Approximately 10% of mothers and fathers were obese, with a BMI of 30 or more.
The researchers found that maternal obesity had little association with the development of autism in the child. However, they found a doubled risk for development of autism and Asperger’s syndrome in the child if the father was obese, compared with a normal-weight father.
“We were very surprised by these findings because we expected that maternal obesity would be the main risk factor for the development of ASD. It means that we have had too much focus on the mother and too little on the father. This probably reflects the fact that we have given greater focus to conditions in pregnancy, such as the growth environment for the fetus in the womb than both environmental and genetic factors before conception,” says Surén.
The researchers adjusted for variables that may also be associated with the development of autism in the child. In addition to adjusting for maternal obesity, they considered education, age, smoking, mental disorders, hormone therapy before pregnancy, use of folic acid, maternal diabetes , pre-eclampsia and the baby's weight at birth.
“Our findings therefore suggest that there may be a genetic link between obesity in the father and the development of ASD in the child,” says Surén.
He points out that genetic mutation may play a role in the development of both extreme obesity and autism. Researchers have shown, for example, that if a section of chromosome 16 is missing this can lead to morbid obesity or developmental disorders in children. Mutations may be a basis for the development of a number of complex syndromes and diseases.
Another explanation may lie in epigenetics. Epigenetic changes do not mean that the gene is altered, but that the gene is activated or inactivated as a result of environmental conditions. Switching a gene on or off at the wrong time and place can lead to adverse consequences for the individual and the epigenetic changes can be passed on to the next generation.
“We still know very little about how epigenetic changes in germ cells are affected by obesity or other environmental factors but animal experiments have shown that obese males have offspring with altered gene expression in early growth regulation,” Surén said.
The first study is published in the May issue of Pediatrics.