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PKU screening: changing lives for 40 years

Hundreds of children and adults have been saved from severe mental retardation over the past 40 years thanks to national newborn screening for PKU, a rare metabolic disorder. The blood test is performed on all newborns while still in the hospital and the test is often repeated again at two weeks of age. First begun in the 1960s, PKU, short for phenylketonuria, has become a model for screening of rare diseases and preventing consequences through treatment.

• incidence and prevalence of PKU and similar disorders
• whether existing newborn screening strategies were effective in diagnosing the disorder
• whether screening was cost-effective
• what treatments were used and whether they were effective at preventing consequences of PKU

What is PKU?
PKU is one of the more common conditions that belong to a group of rare disorders called inborn disorders of metabolism. Some are fatty-acid disorders; others involve a toxic buildup of amino acids or organic acids. Of the four million or so babies born in the U.S. each year, about one in 4,500 has one of these disorders. PKU occurs in one out of every 15,000 births in the U.S. and there is a slightly higher incidence in white and Native Americans.

During normal digestion, enzymes in the digestive tract break down protein into their component amino acids that the body can use for energy and for building new body protein. However, a child with PKU lacks a certain enzyme that breaks down the amino acid phenylalanine (Phe). Without this enzyme, levels of Phe can build up to very high levels in the blood and cause mental retardation.

Drawing conclusions
After months of review, the panel reached the following conclusions:

1) More research is needed to develop better treatment for PKU
The only treatment currently available for PKU is to significantly restrict what the child eats. The diet generally excludes all high protein foods, including meats, dairy products, nuts, most breads and vegetables in the legume family. Special Phe-free foods supply nutrients that the restrictive food choices lack but these can be expensive and hard to get. Research on developing a treatment has focused on gene therapy or developing enzymes that can be taken orally to break down the phenyalalanine in the diet.

2) There needs to be more consistency in screening programs in the U.S.
In all but four states, parents can refuse the test for their infants. The level of Phe used to determine whether a child has PKU varies from state to state. States also vary widely in fees charged for testing, as well as the level of support and follow-up care provided to the child and family, including availability of psychological nursing services, genetic counseling, medical nutrition therapy, parent education about PKU and availability of medical foods and modified low-protein foods.

3) National standards are needed
The panel concluded that treatment guidelines consistent across the U.S. should be established. Infants with blood Phe levels greater than 10 mg/dL should be started on treatment as soon as possible, but no later than seven to 10 days after birth. Frequent monitoring of blood levels is required and the panel recommended that those affected stay on the restrictive diet for life.

4) Treatment should be multidisciplinary, programmatic, lifelong and accessible
Tight dietary control and beginning treatment at an early age-during the first days of life-had profound benefits. Treating PKU is a life-long commitment done best in a setting that brings together all the resources needed. They noted that there should be equal access to treatment for all individuals with PKU.

5) Research is needed to assess long-term outcomes
Since the oldest people with treated PKU are only in their early 40s, more research will be needed to determine which treatment programs result in the best long-term outcomes. Additionally, long-term studies looking at the effects of aging on people with PKU should be performed.