A protein that is helpful to embryo survival may actually be harmful to babies born to diabetic women, according to a recent study released by a Harvard Medical School (HMS) affiliate.

Past research has found that diabetic women are two to five times more likely than women with normal blood sugar levels to have babies with birth defects.

In the recent study, which was conducted on mice, HMS associate professor Mary R. Loeken and her colleagues at the Joslin Diabetes Center identified the expression of the glucose transporter Glut2 early in embryonic development as a factor in this disparity.

However, because Glut2 is necessary for the health of both embryo and mother, Loeken said that a treatment blocking Glut2 is not viable.

It is standard medical knowledge that glucose transporter Glut2 moves glucose from blood to cells, allowing faster absorption, according to a press release from the Joslin Diabetes Center.

After birth, Glut2 is concentrated in the pancreas and liver, which use Glut2 to detect high levels of glucose in the blood.

At high concentrations of blood glucose, Glut2 increases the velocity with which glucose is taken into the cell.

Loeken found that Glut2 is expressed unexpectedly early in the embryonic development of mice, exposing the embryo to the abnormal amount of glucose present in the mother’s blood.

In previous studies, Joslin researchers have found that birth defects occur because when the embryonic cells break down the excess glucose, genes that control essential developmental processes are inhibited.

But even though Loeken found that diabetic mice lacking the Glut2 transporter were less likely to have offspring with birth defects than those with functioning Glut2, the study also found that embryos were less likely to survive if they lacked Glut2.

What remains to be seen is how long the embryo must be exposed to these high glucose levels to be affected, according to Florence M. Brown, who is the co-director of the joint Joslin and Beth Israel Deaconess Medical Center Diabetes and Pregnancy Program.

“It is unclear how long the target tissues must be exposed to high glucose levels for birth defects to occur, or if transient spiking of blood glucose is enough,” wrote Brown in an e-mailed statement.

Brown added that because the experiment was conducted on mice, the relationship between Glut2 and human birth defects is also unknown.

However, Loeken said that the study will be helpful in determining what level of blood glucose should not be exceeded during pregnancy.