Genes may link birth weight, diabetes in adulthood

By Joene Hendry

NEW YORK (Reuters Health) - A large study of Swedish twins indicates that a common genetic cause underlies both low birth weight and the propensity to develop type 2 diabetes.

While low birth weight is more common among individuals with type 2 diabetes, poor fetal nutrition and other environmental factors leading to low birth weight do not "cause" diabetes, according Dr. Stefan Johansson and colleagues.

Rather, data from their study suggest that common genes may be responsible for both reduced fetal growth and development of diabetes in adulthood, said Johansson, of the Karolinska Institute in Stockholm.

In the journal Epidemiology, Johansson's group describes their study of 18,230 fraternal and identical twins (592 with type 2 diabetes), born between 1926 and 1958. Twins share the same early environment, but identical twins, of course, also share the same genetic makeup, whereas fraternal twins have different sets of genes.

The investigators first examined all twins as independent individuals, Johansson told Reuters Health. Similar to previous research, the current analysis found that low birth weight was more common among adults with type 2 diabetes.

Johansson's group further analyzed the twins as pairs when one had diabetes and the other did not. This showed a continued link between low birth weight and diabetes among fraternal twins but no such link between identical twins who share all their genes.

Explaining what this means, Johansson said: "Within a fraternal twin pair, the lighter twin would face an increased risk of diabetes ... But within an identical twin pair, the lighter and the heavier twin have the same risk of developing diabetes later in life."

These findings support the idea that genetic factors are important in understanding the link between birth weight and type 2 diabetes, and environmental factors, such as poor fetal nutrition, are less important than previously proposed, commented Johansson.

SOURCE: Epidemiology, September 2008.