The condition that is the ‘opposite’ of autism

They’re too open and trusting, especially toward strangers

And people with this condition treat strangers as their new best friends.

Now, William Syndrome (WS) is giving clues to our evolutionary past and what makes us human.

It is a rare genetic condition that affects approximately 1 in 7,500 people, and these individuals feel an overwhelming love and warmth for every single person that they meet.

The innate desire to hug and befriend total strangers is common among people with WS.

This is because they are extremely affectionate, empathetic, talkative and gregarious.

Everyone that they meet they treat as their new best friend. However, being so friendly has a downside.

People with this condition struggle to retain close friendships and are prone to isolation and loneliness, more often than not.

And one worrying element of it is that they’re too open and trusting, especially toward strangers. This means that they don’t realise when they are in danger, and are vulnerable to abuse and bullying as a result.

Alysson Muotri, a professor of paediatrics and cellular and molecular medicine at the University of California, San Diego, says that "it's very easy for someone to fool a person with Williams Syndrome and take advantage of them, because they are so trusting.”

“They give themselves to anybody without prejudice, which seems like a lovely trait, but at the end of the day there is a reason why the human brain evolved to be a little bit suspicious of a new person. You don't know if that person is there to hurt you or to love you, and they [a person with WS] cannot make that distinction,” he adds.

Experts say that many people who have William Syndrome suffer from severe anxiety, and few of them live independently as adults.

The condition is also accompanied by health problems such as cardiovascular disease, developmental delays and learning disabilities.

For example, many people with William Syndrome have a lower IQ than average.

Scientists have learned more about WS over the last decade, as it’s offering a unique window into how some of the traits that make us human evolved.

These includes traits such as kindness, trust, and friendliness.

Where people with WS differ is that the process called ‘recombination’ - which occurs where genetic material is swapped between matching pairs of chromosomes - goes wrong.

This happens as a whole section of DNA from one copy of chromosome seven is accidentally deleted. As a result, people with WS are missing one copy of between 25-27 genes.

Humans have 46 chromosomes, organised into 23 pairs, and the ‘recombination’ process occurs during sperm or egg development.

However, pinpointing the single gene, or genes, responsible for the increased friendliness of people with WS has proved more elusive. One theory is that BAZ1B could have a role as well.

Meanwhile, other scientists believe that a gene called GTF2I could be responsible. For example, research has shown that individual animals who lack GTF2I tend to be more social than other members of their species.

This is the case with dogs, who contain a variant of the GTF2I gene. This could the dogs’ overt sociability and friendliness compared to wolves.

Meanwhile, people who have a duplication of the gene tend to develop a form of autism characterised by social phobia.