Gene links low birth weight to diabetes

Scientists have uncovered a genetic link between low birth weight and developing type-2 diabetes in later life.

The international team analysed 19 previous studies on pregnancy and birth weight in 38,000 Europeans. They found that babies with low birth weights had SNPs (single nucleotide polymorphisms) in two locations. One was on a gene called ADCY5.

Variations in the ADCY5 gene were linked to diabetes by a study published in Nature Genetics earlier this year. Inheriting deleterious variants of ADCY5 increased the risk of developing type-2 diabetes by 25 per cent. This latest study, also published in Nature Genetics, provides the first evidence that babies who inherit a risk-conferring variant of ADCY5 also weigh less at birth.

Professor Mark McCarthy, who led the study at the University of Oxford, UK, said: 'It was a surprise to see such strong genetic effects for a characteristic such as birth weight, which is subject to powerful influences from so many environmental factors'.

Nine per cent of the babies in this study inherited two copies of the risk variants in both of the regions identified. These babies were on average 113g lighter than the babies who inherited only one copy of the risk variants or none at all. This decrease in weight was said to be equivalent to a pregnant mother smoking four or five cigarettes a day in the last three months of pregnancy.

The link between low birth weight and type-2 diabetes was initially attributed to environmental factors, such as the pregnant mother's diet. But this study shows a genetic contribution.

Dr Rachel Freathy, who was involved in the study at the Peninsula Medical School in Exeter, UK, said: 'It is now important for us to establish how much of the association is due to our genes and how much is due to the environment, because this will inform how we target efforts to prevent the disease'.