• Asthma
• Tobacco and the lung
• Asthma Mechanisms

Visiting the iniquity of the fathers upon the children, and upon the children’s children, unto the third and to the fourth [generation]. Exodus 34:7, King James Bible

There can be few readers of Thorax who remain unaware of the body of evidence that supports a detrimental effect of tobacco smoking by pregnant women on the subsequent health and development of their offspring. Childhood disorders associated with mothers smoking when pregnant include low birth weight, sudden unexplained death in infancy, asthma1 and a number of neurobehavioural outcomes, although whether all these reported associations are truly causal has been questioned. Such outcomes could be ascribed to direct toxic effects of tobacco smoke constituents on the fetoplacental unit with consequences for fetal organ development which might manifest through the life course. For example, intrauterine exposure to maternal smoking is associated with low lung function2 and increased respiratory symptoms3 in infancy and, through reduced birth weight, low FEV₁ and COPD in adulthood.4 However, in seeking the developmental origins of respiratory disease, we now have to extend our horizons to more distant ancestry, when lifestyle and behavioural practices now recognised to be harmful were socially (and medically) acceptable. In this issue of Thorax, Maria Magnus and colleagues report an association between grandmothers’ smoking when pregnant and an increased risk of asthma in their grandchildren even when the mother herself did not smoke when pregnant with the index child.5

These results came from the analysis of observational data in the Norwegian Mother and Child Cohort Study (MoBa), a very large, prospective birth cohort of around 100 000 women and their children with asthma outcomes ascertained from questionnaires and from linkage to a national prescribing registry. Between 25 000 and 45 000 children had reached the age of 7 years and …