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Susan Warhus, MD

Your question:
Can someone with PKU breastfeed? I heard if I have children, I won't be able to because I have PKU.

The expert answers:
Phenylketonuria (PKU) is an inherited condition that renders the body unable to break down an important protein called phenylalanine (Phe). This genetic disorder can lead to serious brain development problems. Fortunately, by following a special diet low in Phe, individuals with PKU can avoid brain damage. Babies and children must also adhere to this special diet in order to avoid mental retardation.

The current recommendation is for individuals with PKU to remain on this special diet for their entire lifetime. This is especially important for women of childbearing age. That's because increased Phe levels during pregnancy may adversely affect the developing baby.

A dietician or other healthcare professional can provide you with specific information on the PKU diet. In general, foods that contain high levels of Phe such as meats and dairy products should be avoided. Most grains, fruits, vegetables and other low protein foods are usually okay.

PKU cannot be passed to the baby during breastfeeding. The only way to acquire PKU is to be born with those genes. So unless your baby is born with PKU, breastfeeding should not be a problem. If your baby is born with PKU, you may be able to breastfeed providing you stay on the special PKU diet. The baby's doctor can measure the Phe level in the baby to assure it is not elevated. There is also a special low Phe infant formula available for babies with PKU.

So what are the chances of your baby having PKU? Naturally, it depends on the genetic traits of both the mother and father. Like many genetic traits, people can be placed into one of three PKU categories: those with PKU, those who are genetic carriers of PKU, and those who do not have or carry PKU.

Since you have PKU, if you have children with someone who also has PKU, then all of your offspring will have PKU.

If you have children with someone who is a carrier of PKU, there is a 50 percent chance for each offspring to have PKU. If you have children with someone who does not have or carry PKU, then none of your children will have PKU, but they will all be carriers. Carriers are healthy, but can pass the PKU gene to their children. All babies are tested for PKU shortly after they are born. A genetic counselor or other healthcare professional can provide you with additional information.

The information provided above is derived from the Organization of Teratology Information Service (OTIS). For a more detailed discussion of maternal PKU and pregnancy, please refer to their web site,

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