Little is known about Phelan-McDermid Syndrome, the rare genetic condition which affects only 1,300 people worldwide.

But one Highgate mother of a child sufferer is looking to change that, by leading an awareness-raising mission to try and get better support for families affected by the syndrome.

Alison Turner, whose 11-year-old son Gibson has the condition, said: “Because it’s such a rare condition, parents become the experts.”

The 47-year-old, who is chairwoman of charity Phelan-McDermid Syndrome Foundation UK, added: “We find more out about it from other parents than the medical community. That’s just the way it is because it’s so rare.”

One of the ways Ms Turner and the charity is providing better support for families affected by the condition is to organise semi-regular family days, the last of which was held last week at Brookfield Primary School in Chester Road, Highgate.

More than 200 people from more than six countries gathered to share their experiences of coping with a family member who has the syndrome.

Guest of honour was Dr Katy Phelan, the geneticist who co-discovered the condition.

Only 120 people in the UK have the syndrome, and sufferers are often unable to speak, have severe learning difficulties and are on the autism spectrum.

So rare is the syndrome that even most doctors have never heard of it.

Ms Turner’s son Gibson, who needs 24-hour care and doesn’t speak, was diagnosed just before the age of two.

“I didn’t have any support,” said the married mother-of-three, of Highgate West Hill. “It took about 18 months to come to terms with it. Doctors were giving me information but I didn’t understand it. I woke up feeling physically sick everyday but we changed our approach and now we have a happy, relatively healthy, boy and a hugely supportive community.”

As head of the charity working to support families affected by the condition, Ms Turner is issuing 7,000 easy-to-read pamphlets about the condition to hospitals and GP surgeries to inform more people about it. The charity also has a database of its sufferers to aid geneticists with further research into the condition.

Ms Turner’s long-term aim is to ensure her son and others like him can lead fully integrated lives.

She said: “When Gibson is an adult, it will probably be quite scary because he will be flailing his arms around people, but it is so important for them to be part of the community. Accepting them socially, that’s the biggest thing, and understanding that families will need extra help.”