Autism and a developmental disorder marked by hyper-sociability and musical skill may be flip sides of the same genetic coin, scientists have learned.

Williams syndrome is a rare condition marked by “elfin” facial features and some characteristics which appear the reverse of those seen in autism.

As well as having heart problems, children born with the disorder are unusually cheerful and at ease with strangers.

They have strong language skills, can be overly sociable, and display what is known as a “cocktail party” personality. In addition, they have sensitive hearing and an unusual aptitude for music.

Autistic children, on the other hand, have real problems empathising, communicating and socialising with others.

New research has now shown that the same small section of DNA appears to be involved in both autism and Williams syndrome, but in opposite ways.

Matthew State, professor at the Yale University in the US, said: “In autism, there is an increase in the chromosomal material, an extra copy of this region, and in Williams syndrome, there’s a loss of that same material.

“What makes this observation particularly interesting is that Williams syndrome is known for a personality type that is highly empathetic, social, and sensitive to the emotional state of others. Individuals with autism often have difficulties in the opposite direction. This suggests that there is an important key in that region to understanding the nature of the social brain.”