By Amy Norton
NEW YORK (Reuters Health) - For women with the rare genetic disorder phenylketonuria, a new study highlights the importance of sticking with therapy before and during pregnancy.
People with phenylketonuria, or PKU, cannot process a protein called phenylalanine, which is found in most foods.
Newborns are routinely screened for PKU because it can cause developmental disabilities if it's not treated, which means following a special, low-protein diet and taking supplements free of phenylalanine.
At one time, doctors thought people with PKU could go off the diet once they reached their teen years. But now they advise everyone with the disorder to stick with the diet for life, possibly along with medication that boosts the body's tolerance to phenylalanine.
One reason is that if a woman with untreated PKU becomes pregnant, it could harm the baby.
And the new study, reported in the American Journal of Clinical Nutrition, confirms that.
Researchers found that across nearly 200 pregnancies reported in the medical literature, women with untreated PKU were more likely to have a baby with a small head size, facial deformities or eventual mental impairment versus women whose PKU was treated.
The findings underscore the importance of the lifelong PKU diet, according to senior researcher Dr. Johannes J. Duvekot of Erasmus Medical Center in Rotterdam, the Netherlands.
Therapy before conception is key, he told Reuters Health in an email, because lowering the body's phenylalanine levels takes some time.
For their study, Duvekot and his colleagues looked at reports on PKU-affected pregnancies in the medical literature, as well as records for 15 women seen at their medical center since 1995.
Of 196 pregnancies, 126 were in women with untreated PKU, while the rest were in women who were on therapy.
In some cases, Duvekot said, the untreated women had gone off of their PKU diet as teenagers. In some others, the women were from countries where PKU is not as closely managed as it is in Western countries.
Of babies born to moms with untreated PKU, 46 percent had a small head size at birth. That compared with less than 20 percent of infants whose mothers had treated PKU.
When it came to mental or developmental disabilities, 47 percent of children born to untreated moms were affected -- versus about one-quarter of children whose moms had PKU treatment.
Babies born to untreated moms also had a higher rate of facial deformities. But only phenylalanine levels in a mother's first trimester were related to the risk of facial deformities.
That suggests that PKU treatment has to start before the first trimester to prevent problems in facial development, according to Duvekot's team.
The standard advice in many countries is for people with PKU to continue their diets and medication for life, Duvekot pointed out. And women should be aware of the particular importance of that before and during pregnancy.
It's estimated that between one in 10,000 and one in 15,000 babies are born with PKU in the U.S., where all newborns are screened for the disorder.
SOURCE: http://bit.ly/As6NgW American Journal of Clinical Nutrition, online December 28, 2011.