Could Sperm Mosaic Mutations Be Linked to Autism?
According to a recent study, more than five percent of sperm cell mutations scientists believed to have appeared in a child with autism spectrum disorder (ASD) could, in fact, be inherited.
Such mutations were seen in a subset of a father’s sperm cells, according to an unpublished study conducted by the University of California, San Diego. These results were presented last month by Dr. Martin Breuss, a postdoctoral fellow in Joseph Gleeson’s lab at the university to the 2017 American Society of Human Genetics Annual Meeting in Orlando, Florida.
According to Dr. Breuss, testing the harmful mutations in sperm may help in estimating the risks that the man could pass them on to his children. The small sample, which only had four families as subjects, suggests that the risk could be ten times higher compared to the one percent rate that was proposed by studies in the past.
There have been other studies conducted that are related to the father’s reproductive system and its link to autism. A genetic study by DeCODE Genetics in Iceland authored by Augustine Kong revealed that older men are more likely to have children with autism or schizophrenia. This is because they are more likely to pass on to their offspring more random genetic mutations which increase the risk for such conditions. It was also evident in the study that an older father contributes to almost all of the child’s random genetic mutations compared to the mother. The father’s age during the conception of the child can be held accountable for 97 percent of the new or de novo mutations that are found in the offspring.
De novo mutations have been linked to autism cases. This type of mutation can be observed in the blood of the child but not in both parents. It is because of this that mutations have been assumed as single events that started from the egg or sperm. De novo mutations are those changes in the DNA that occur spontaneously in the egg or sperm cells during the period of conception. The majority of people are born with these mutations, but most of the changes are considered harmless.
The findings of DeCODE Genetics could explain the rise in the diagnoses of autism in the recent years. Approximately 1 in 68 children has been identified with ASD according to the Centers for Disease Control’s (CDC) Autism and Developmental Disabilities Monitoring (ADDM) Network. The results of the study counter the assumption that a mother’s advanced age causes developmental and psychiatric disorders.
Dr. Breuss said that the people behind his study believed that mosaicism in sperm had been underestimated. He added that those estimates were based on different cell types, such as blood. In this study, sperm samples were collected from 12 men, each one having a child with autism. It was observed that each child had a spontaneous mutation in a gene which is strongly linked to autism. These genes are mostly found in the brain, and they have been observed to be highly mutated in many children with autism.
According to Breuss, the findings of the study suggest that the mutations, contrary to the other studies, were not de novo. They were all inherited from the father’s sperm. He added that de novo is often determined based on the ability to detect such variants using standard approaches. Most often these are considered insensitive or merely targeting tissues that are not likely to have the mosaic variant.
Researchers continue to analyze additional samples. There is also a plan to explore the possibility that mosaic mutations in sperm have an effect on particular functions like cell growth and if mosaic mutation is affected by the father’s age.
New studies may be on the horizon that may be able to add more light to mosaic mutations and other genetic factors that may cause autism. The more studies conducted on this matter, the better the chance for understanding autism.