An abnormality in one's sex chromosome in the form of an extra Y chromosome has been related with a doubled risk of having autism, according to a study that offered a "new explanation" for why autism is more prevalent in men.

The Y chromosome should be looked at more closely for identifying autism risk factors, researchers said.

Sex chromosomes determine an individual's biological sex -- men usually carry XY chromosome in their cells, while women are known to carry XX chromosome.

However, some individuals carry an abnormal number of X or Y chromosomes, such as XXY or XYY, which is a genetic condition known as 'sex chromosome aneuploidy'.

Autism, a neurodevelopmental condition in which one displays repetitive behaviours and has affected social skills, has been studied to be nearly four times more common among men, compared to women, indicating a strong gender aspect to the skewed ratio.

Researchers, including those from the Autism and Developmental Medicine Institute, US, looked at autism diagnoses in people having abnormal sex chromosomes and found that those having an extra Y chromosome -- XYY or XXY -- were twice as likely to be diagnosed with autism.

Having an extra X chromosome did not affect autism risk, they said. The team analysed genetic and autism diagnosis data on 1,77,416 patients, of which 350 had abnormal sex chromosomes.

Further, having XYY chromosomes was found to increase autism risk more than having XXY.

Published in the journal Nature Communications, the results suggested a risk factor linked to the Y chromosome, as opposed to the protective effect known to be associated with the X chromosome, the authors said.

Protection provided by the X chromosome are considered to lower risk of autism in women, according to a predominant theory in the research field called the 'female protective effect'.

The study's findings pointed towards the need to look for autism risk factors on the Y chromosome, rather than limiting oneself to protection rendered by the X chromosome, the authors said.

Therefore, they called for further research to identify specific autism risk factors associated with the Y chromosome.

The participants were included from the Simons Foundation Powering Autism Research (SPARK) study and MyCode Community Health Initiative, both in the US.

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