Scientists today hailed a 'breakthrough' after uncovering a major potential treatment for postnatal depression. 

Until now, experts were unsure exactly what triggers the condition despite the fact that one in ten women are affected before or after giving birth.

But researchers in the US and UK have discovered those affected may be missing genes that allow the body to produce the hormone oxytocin. 

Dubbed the 'cuddle hormone', oxytocin is released during childbirth, breastfeeding and in response to hugging, helping stimulate feelings of attachment. 

Without sufficient amounts, new mothers may struggle to bond with their baby, triggering low mood. Now experts suggest developing new oxytocin medicines may be a way to help combat these symptoms.

Professor Sadaf Farooqi from the Institute of Metabolic Science at the University of Cambridge: 'We have made a breakthrough in understanding postnatal depression, a serious health problem about which very little is known despite many decades of research. 

'And importantly, it may point to oxytocin as a possible treatment for some mothers with this condition.

'This research reminds us that many behaviours which we assume are entirely under our control have a strong basis in biology.'

The researchers, led by scientists at the University of Cambridge and Baylor College of Medicine in Texas, made their discovery while looking at the genes of two boys from different families.

Both were living with severe obesity and also suffered from anxiety, autism, and behavioural problems.

They found they each were missing a single gene known as TRPC5.

Their mothers were also missing the gene. Both mothers were obese and both had suffered postnatal depression.

Examining the missing gene in studies on mice, the scientists then discovered that male mice with a defective form of the gene displayed the same problems as the boys. 

This included weight gain, anxiety, a dislike of social interactions and aggressive behaviour.

Female mice showed similar behaviours. 

And when they became mothers they also displayed depressive-like behaviour and 'impaired care of offspring,' the experts said.

Writing in the journal Cell, researchers said they found TRPC5 acts on the nerve cells that produce the hormone oxytocin.

Deleting the TRPC5 gene from these oxytocin neurons led to otherwise healthy mice showing signs of anxiety, overeating, impaired social skills and, in the case of mothers, postnatal depression-like symptoms.

By making changes to the TRPC5 gene so that more oxytocin was produced, the scientists 'reversed' these symptoms: mice began behaving normally a lost weight. 

The experts suggest treatments that help increase oxytocin the body may produce similar results in humans, although more research would be needed.  

Oxytocin is produced in the hypothalamus part of the brain and secreted into the bloodstream by the pituitary gland. 

Studies have shown oxytocin also may have anxiolytic properties, meaning it may help reduce anxiety.

Previous researchers has also found when oxytocin is administered to people with autism via a nasal spray, it made them more sociable.

Postnatal depression causes intense feelings of sadness, anxiety and exhaustion that usually begin two to three days after the birth and can last months.

Other symptoms include insomnia, loss of appetite, intense irritability and difficulty bonding with the baby.

In rare cases, an extreme disorder called postpartum psychosis may develop.

Existing treatment includes talking therapy or traditional antidepressants, but these can take weeks to kick in.

Latest NHS data shows 26 per cent of adults in England are obese and a further 38 per cent are overweight but not obese.

Experts have pointed to a lack of exercise, and poor diets high in ultra-processed food, as being key drivers in the UK's obesity epidemic.

Dr Yong Xu, an expert in molecular and cellular biology from Baylor College of Medicine, said: 'What we saw in those mice was quite remarkable. 

'They displayed very similar behaviours to those seen in people missing the TRPC5 gene, which in mothers included signs of depression and a difficulty caring for their babies. This shows us that this gene is causing these behaviours.'

Professor Farooqi added: 'There's a reason why people lacking TRPC5 develop all of these conditions.

'Our work shows that TRPC5 acts on oxytocin neurons in the hypothalamus to play a critical role in regulating our instincts.'