Born this way ... scientists isolate the gene responsible for bratty behaviour.

Scientists may well have found what mothers have suspected exists for a long time — a gene for brattiness.

The researchers from Arizona University examined the non-compliant and aggressive behaviours of 138 children aged between 18 and 54 months, as well as the quality of their mothers' parenting behaviour.

They also tested the children for variations in the SLC6A4 gene, which is known to transport serotonin, an important natural chemical messenger in the body linked to well-being.

They found the quality of parenting was only related to non-compliance in children with particular variations.

"The findings support the notion that SLC6A4 haplotypes index differential susceptibility to variability in parenting quality, with certain haplotypes showing greater reactivity to both supportive and unsupportive environments," they wrote in the journal Developmental Psychology.