Although people with autism have more cancer promoting genetic mutations, researchers have discovered – to their surprise – that they are significantly less likely to develop the disease, a new study shows.

This new study also found that the protective effect is highest in children and younger teens, and declines as people age.

Autism spectrum disorder is a general term for a group of disorders that affect brain development. Autism is characterized by impaired social interaction, verbal and nonverbal communication skills, and repetitive behaviors.

Previous research had found that there is an overlap between some genes associated with autism and others that are implicated in many inherited cancer syndromes caused by mutations in a single gene.

Researchers at the University of Iowa looked at data from 1,837 patients with autism and compared these to 9,336 patients with any other diagnosis, to see what proportion of each group had been diagnosed with cancer.  They found that 3.9 per cent of patients without autism had cancer. But in both men and women with the spectrum disorder, this figure dropped to 1.3 per cent.

They found no link between autism and diseases such as high blood pressure and diabetes or common conditions including heartburn, allergies, eczema, or short stature.

The researchers say they have no explanation for the paradoxical findings, but the study raises possible new ways to find treatments for both conditions, and that scientists are already looking at whether anti-cancer drugs could help people with autism.

"It's a very provocative result that makes sense on one level and is extremely perplexing on another," says Dr. Benjamin Darbro of the study, which appears in PLOS ONE.