What is Mild Hyperphe?

Mild Hyperphe is an inherited condition in which a person's body is unable to properly utilize one part of protein found in food. This condition causes mildly increased levels of phenylalanine in the blood. There are no known problems associated with having Mild Hyperphe as a child so dietary treatment is usually not required then. However, research suggests special attention might be needed for the woman with Mild Hyperphe during pregnancy to protect her babies from birth defects.
Hyperphe is an abbreviation of the medical term Hyperphenylalaninemia (pronounced hyper-fenel-al-ah-ninemia). This long medical term can be divided into three parts and defined as follows:

Hyper: means high
Phenylalnine: is an amino acid (a part of protein) found in food
Emia: refers to the blood

How Did I Get Mild Hyperphe?

Genes are responsible for your characteristics, such as eye color and height. Genes are also responsible for instructing the cells in the liver to make the enzyme that changes PHE to tyrosine. When the gene responsible for making this enzyme is altered, Mild Hyperphe occurs. Below is a simple illustration of how the altered gene was passed from your grandparents to your parents and to you.

Genes are units of inheritance found in body cells. Genes come in pairs in your cells with each parent contributing one gene to the pair in each cell. A person who has one "normal" gene and one altered Mild Hyperphe gene is called a carrier.

Generation I represents the possible genetic makeup of your grandparents. One of your maternal grandparents and one of your paternal grandparents are carriers of the Mild Hyperphe gene. One in 70 persons are carriers of the Mild Hyperphe gene.

What Are the Effects of Mild Hyperphe on an Unborn Child During Pregnancy?

There are no known problems associated with having Mild Hyperphe as a child so treatment is not needed then. However, research suggests special attention may be needed for the woman with Mild Hyperphe during pregnancy to prevent birth defects.

In 1984, the Maternal PKU Collaborative Study began collecting information on Hyperphe during pregnancy. Women with various types of Hyperphe, including Mild Hyperphe, were enrolled and followed during pregnancy by the Study. The results show that women with Mild Hyperphe should be followed by a PKU center before and during pregnancy. The center monitors the woman's diet and blood PHE levels and, if necessary, puts her on a diet to avoid possible damage to the baby.
The potential damage for the unborn baby during pregnancy works this way. As blood flows from the mother through the placenta during pregnancy, nutrients, including PHE, are transferred to the baby. The placenta concentrates some nutrients, like PHE, to help the baby grow. The blood PHE level may increase 1½ times in the baby. For example, a mother's blood level of 7 mg/dL (420 mmol/L) may be concentrated by the placenta to 11 mg/dL (660 mmol/L) before passing on to the baby as illustrated in Figure 4. Blood PHE levels that are too high place the baby at risk for birth defects.