Children who inherit a certain version of the insulin gene from their father stand a greater chance of becoming obese, according to a new study. The findings add to the evidence that insulin levels before birth can alter the risk of obesity.
Insulin, a hormone produced by the pancreas, helps cells absorb sugar from the blood. The insulin gene is "imprinted" prenatally, meaning only one copy is active in the fetus. People inherit two copies of every gene, one from the mother and one from the father. In imprinted genes, one copy is turned off, either temporarily (in the womb) or permanently. Part of the insulin gene determines how much insulin is produced; the gene is imprinted so that only the father's version is active before birth.
Pediatric endocrinologist Pierre Bougnères of Hôpital Saint Vincent de Paul in Paris wondered whether prenatal activity of this gene might contribute to childhood obesity. To test this, his team looked at the genes of 238 children whose body mass index was above the 85th percentile by age 6 and compared them with the genes of 106 lean siblings. By cross-checking both parents' genes, the team could figure out which version of the gene came from which parent.
As expected, mom's contribution made no difference as to whether a child was lean or obese. But obese children were twice as likely to have inherited the insulin-inducing version of the gene from their fathers than another version of the gene that pumps out less insulin, the researchers report in the September issue of Nature Genetics. This suggests that the amount of insulin present during fetal development plays a role in childhood obesity. Lean children were equally likely to inherit either version from Dad.
"It's very exciting," says molecular biologist Gudrun Moore of Imperial College in London, but she cautions that the researchers need to show that these versions of the gene actually correlate with fetal levels of insulin.
Abstract of the
Explanation of genetic imprinting, from Genetic Drift newsletter
Introduction to insulin, from EndocrineWeb
Gudrun Moore's January 2001 Diabetes paper showing that the insulin gene is imprinted