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Gene studies indicate paternal age and gender as risk factors for autism

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Two expansive studies published this week reveal genetic vulnerabilities associated with autism spectrum disorder (ASD) and other psychiatric disorders.

The first study, published Wednesday in JAMA Psychiatry, finds that children born to older fathers, those 45 or older, have an increased risk of being diagnosed with ASD by a factor of three-and-a-half. In addition, the risk of diagnosis with attention deficit hyperactivity disorder (ADHD) is increased by 13 times, bipolar disorder by 25 times, as well as an increased risk of psychotic disorder, suicidal behavior, academic deficits and substance abuse problems.

The study looked at over 2.5 million genetic records of people born between 1973 and 2001, controlling for factors such as parental education and income levels, comparing children born from fathers 45 years of age or older with fathers 20 to 24 years old.

In 2012, researchers also found a link between paternal age and risk for autism, citing that the mutation rate in genetic material, known as "de novo mutations," in children is determined by the age of the father at conception. Part of this risk may be attributable to the fact that sperm is constantly being produced throughout the lifespan, increasing the risk of mutation every time a cell divides.

A second study published Thursday in the American Journal of Human Genetics indicates that boys have an increased genetic vulnerability of being diagnosed with autism spectrum disorder (ASD) and that girls possess a genetic resilience to abnormalities caused by genetic mutation.

Researchers from the University of Washington School of Medicine, in conjunction with the University of Lausanne, looked at nearly 16,000 DNA samples and sequencing data sets from people with neurodevelopmental disorders, including ASD, and genetic data from almost 800 families affected by autism. They analyzed individual variations in the number of copies of specific genes and nucleotides, the building blocks of DNA.

The study found that autism affects four boys for every one girl, increasing to seven boys for every one girl for diagnoses on the high-functioning end of the autism spectrum.

Females diagnosed with a neurodevelopmental disorder, including ADHD, schizophrenia, as well as ASD, had more harmful genetic variations than males who were diagnosed with the same disorder. This indicates that the female brain appears to possess an inherent resilience to genetic variations, requiring more extreme genetic mutations than the male brain to produce neurodevelopmental disorders.

While this broadens the focus of research from X chromosome to the entire genome, it does not take into account the possible effects of exposure to sex hormones early on in life, namely testosterone.

Both of these studies provide insight to families in determining the risk of their child being diagnosed with a neurodevelopmental disorder later in life, including ASD. Early genetic testing may indicate the presence of mutations or abnormalities, leading to earlier diagnosis and intervention.

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