Strict parenting alters children's DNA readings. These changes can become "hard-wired" into the DNA of harsh-parented children, increasing their biological risk for depression in adolescence and adulthood.

"We discovered that perceived strict parenting, with physical punishment and psychological manipulation, can introduce an additional set of instructions on how a gene is read to become hard-wired into DNA," Dr Evelien Van Assche said at the ECNP Congress in Vienna.

"These changes may predispose growing children to depression. Having a supportive upbringing reduces this "Assche continued.

The University of Leuven researchers compared 21 adolescents who reported good parenting (supportive and allowing autonomy) to 23 who reported harsh parenting (for example, manipulative behaviour, physical punishment, excessive strictness).

Both groups' mean age was 14. Both groups had 11 boys, indicating a similar age and boy-girl ratio.

Many harsh parents showed subclinical depression.

The researchers then measured methylation at more than 450,000 locations in each subject's DNA and found that harsh upbringing significantly increased it.

Methylation is a normal process that changes how your DNA is read by adding a small chemical molecule to it. For example, methylation may increase or decrease a gene's enzyme production.

Methylation variation increases depression risk. She said, "We relied on identical twin research.

Two independent groups found that the twin with major depression had a higher DNA methylation range for most of these hundreds of thousands of data points than the healthy twin."

Dr Van Assche (now at the University of Munster, Germany) added, "The DNA remains the same, but these additional chemical groups affect how the DNA instructions are read."

"Those who reported harsher parenting showed a tendency towards depression, and we believe that this tendency has been baked into their DNA through increased variation in methylation," Dr Van said.

"We are now seeing if we can close the loop by linking it to a later diagnosis of depression and perhaps use this increased methylation variation as a marker, to give advance warning of who might be at greater risk of developing depression due to their upbringing," Dr Van said.

"In this study, we looked at harsh parenting, but any significant stress will change DNA methylation, which may lead to depression later in life. However, a larger sample must confirm these results," Dr Van further added.

Professor Christiaan Vickers, Department of Psychiatry, Amsterdam University Medical Centre, said, "This research helps explain how childhood trauma affects mental and physical health throughout life. Understanding who is at risk and why strict parenting has different effects is valuable."

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