Children with hyperactivity disorder often go on to become smokers – and now researchers think there is a genetic link underlying this.
Researchers think they have pinned down a gene which may lie behind this link.
Reporting in the Archives of Disease in Childhood, they name a DNA sequence called rs 1329650.
This is significantly likely to be passed on from parents, they say.
The study involved some 454 children and 394 mothers. The research showed a large number of the women, some 171, had smoked in pregnancy.
Children with the "smoking" DNA were also likely to perform badly on tasks requiring brain power and concentration, the researchers say – and this was not affected by a mother’s smoking.
Experts say the findings should be considered with caution.
The research was undertaken by Dr Ridha Joober, of the Douglas Mental Health University Institute, Montreal, Canada.
Writing in the same journal, Dr Miriam Cooper and Professor Anita Thapar, of the Institute of Psychological Medicine and Clinical Neurosciences and the Medical Research Council Centre for Neuropsychiatric Genetics and Genomics, Cardiff University, UK, write: "Acknowledging that the same genetic risk variants can have different observable effects in people could help inform discovery of risk variants for childhood developmental/psychiatric disorders for which it can be difficult to assemble very large sample sizes.
Such efforts could help uncover novel biological risk pathways and contribute to explaining why different behaviours and disorders commonly co-occur."
* A second study in the same journal suggests that pregnant women who smoke and are overweight may be responsible for children becoming obese.
Researchers at Nottingham University, UK, analysed some 30 pieces of research into the issue.
Smoking in pregnancy increased the risk by nearly half – although this may be because smoking indicates a tendency to an "unhealthy" lifestyle.
Breast-feeding cut the risk of obesity by 15%.
Researcher Dr Sarah Redsell said: "This will offer a robust starting point for further research that will identify the most appropriate ways in which this information could be useful in healthcare practice.”
Family-based association study of ADHD and genes increasing the risk for smoking behaviours. Archives of Disease in Childhood October 30 2012;doi 10.1136/archdischild-2012-302461
Systematic review and meta-analyses of risk factors for childhood overweight identifiable during infancy. Archives of Disease in Childhood October 30 2012;doi 10.1136/archdischild-2012-302263
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