Researchers from The University of Western Australia, in collaboration with international colleagues, have identified four new genetic regions that influence birth weight providing further evidence that genes as well as maternal nutrition are important for growth in the womb.
The latest study, published in Nature Genetics online, analysed almost 70,000 people of European descent from across 43 separate studies of pregnancy and birth, including from the Western Australian Pregnancy Cohort (Raine) Study. The findings confirmed the three regions previously identified and revealed four new genetic regions that are associated with birth weight.
It has been known for some time that babies born with a lower birth weight are at higher risk of chronic diseases such as type 2 diabetes and cardiovascular disease. Three of these genetic regions are also linked to adult metabolism, helping to explain why smaller babies have higher rates of chronic diseases later in life.
One of the new genetic regions is also associated with blood pressure in adulthood, providing the first evidence of a genetic link between birth weight and blood pressure. Two of the regions are known to be linked to adult height, showing that genes involved in growth begin to take effect at a very early stage.
It's not clear how the genetic regions identified affect both birth weight and adult metabolism, although the findings do offer some clues as to the biological pathways involved. For example, the two genetic regions linking birth weight with type 2 diabetes risk are also associated with reduced levels of insulin. Insulin is the hormone responsible for regulating sugar levels in the blood, but it is also known to have an important role in early growth.
Together, the newly identified genetic regions have a surprisingly large effect on birth weight when compared with known environmental influences. It is well known that maternal smoking in pregnancy leads to lower birth weight babies - if a woman smokes 20 cigarettes a day throughout pregnancy it affects the baby's birth weight by 200g. These seven genetic regions contribute about the same level of influence on birth weight, although through entirely different mechanisms.
The study was part-funded by the National Health and Medical Research Council, The University of Western Australia, Raine Medical Research Foundation, The Telethon Institute for Child Health Research, Curtin University and Women and Infants Research Foundation.