Seven genes influencing birth weight have been identified in research combining the results of smaller studies. Five of these genes may also be linked to health in adulthood.
'These discoveries give us important clues to the mechanisms responsible for the control of a baby’s growth in the womb, and may eventually lead to a better understanding of how to manage growth problems during pregnancy', said Dr Rachel Freathy of the University of Exeter, the lead investigator of the study.
The team used data collected from nearly 70,000 people and used in 50 smaller studies. They searched for genes associated with birth weight variation and confirmed three genes that had been found in previous studies, and identified four new ones.
'The cumulative effect of the genes is surprisingly strong; it's equivalent to the effect of maternal smoking, which is already recognized as lowering a baby's weight at birth', said Dr Struan Grant, co-author and director of the Center for Applied Genomics at the Children's Hospital of Philadelphia, in the USA. However, although the effect of the genes was strongly significant, between them the genes could only explain 0.76 percent of the naturally occurring variation in birth weight.
The researchers considered the mothers' genetic make-up in their analysis as they had to account for the fact that that the mother's DNA rather than her child's might be influencing birth weight. However, it was the genes in the child's DNA, rather than the mother's, that were responsible.
Five of the identified genes also appear to be linked to adult height, blood pressure or type 2 diabetes. Such discoveries could have implications for further research. For instance, it is already known that insulin, while important in diabetes, also plays an important role in fetal development.
As most of the smaller studies included in this meta-analysis only included people of European descent, the researchers specifically checked whether their results also held true by looking at data on populations from other backgrounds. All seven identified genes also affected birth weight in populations of Middle Eastern, East and Southeast Asian, and African origin.
'Our findings add to the growing evidence that events during early growth in the womb can have a significant impact on our health as adults', said Professor Mark McCarthy, a co-author of the study from the Wellcome Trust Centre for Human Genetics. 'However, these genes tell only part of the story. It’s important that we understand how much is down to genetics and how much is due to the environment in which we grow so that we can target efforts to prevent disease later in life'.