September 17, 2014

expert reaction to autism, schizophrenia and birth size

Researchers have reported a link between birth size and two mental health conditions: low birth weight correlated positively with schizophrenia and negatively with autism, while the opposite was true with high birth weight. The study, reported in the journal Proceedings of the Royal Society B looked at a large cohort, but saw small changes in absolute risk.

Dr James MacCabe, Clinical Senior Lecturer in Psychiatric Epidemiology, King’s College London’s Institute of Psychiatry Psychology and Neuroscience, said:

“In this study, the risk of autistic spectrum disorders was increased in babies with either very high or very low birth weight, whereas the risk for schizophrenia was elevated in babies with very low birth weight.

“It is important to put these findings into context.  Firstly, the increased risks were primarily seen in babies at the extremes of birthweight, less than 2.5kg or above 4.5kg.  Secondly, even in these extreme groups, the absolute risks of autism and schizophrenia remained very low.  For example, the risk of autism in the heaviest babies (>4.5kg) was around 1 percent, as compared with a risk of 0.7% in babies of average birth weight.  These results are therefore no cause for alarm even for parents of babies of very high or low birthweight.  The very large size of the study – 1.8 million – which allows these tiny effects to be observed, but the implications for public health are negligible.  The significance of these findings is that these effects, however small, may give us clues as to the origins of these disorders.

“The study appears very well conducted and the findings, whilst small, are likely to be genuine and demand an explanation.  The authors offer an intriguing evolutionary interpretation for the results which is plausible but by no means definitive.”

‘Opposite risk patterns for autism and schizophrenia are associated with normal variation in birth size: phenotypic support for hypothesized diametric gene-dosage effects’ by Byars et al. published in Proceedings of the Royal Society B on Wednesday 17^th September.

Declared interests

None declared