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Pediatric Phenylketonuria (PKU)
What is newborn screening?
"State newborn screening" refers to a test performed on every baby born in every state of the country within the first few days of life, in order to detect serious, life-threatening diseases. State laws require that babies be tested between 2 and 7 days of age, even if the baby seems healthy and has no symptoms of health problems.
How and why is newborn screening performed?
Testing is usually done from a few drops of blood taken from the baby's heel and spotted onto a strip of paper called "filter paper." The filter paper is sent to a laboratory for analysis to determine the presence of a number of medical conditions, including certain recessive genetic diseases. Recessive diseases usually occur when healthy parents who unknowingly carry a gene for a recessive disorder, both pass the gene to their baby at the same time. The baby inherits two copies of the recessive gene and, therefore, is affected with the condition. The specific diseases tested for in the newborn period are often treatable by special diets and/or medications, increasing the baby's chance for a normal life. It is important to detect these diseases as soon as possible to prevent death, intellectual disability, and other disabilities.
For those conditions where a special diet is required, such as phenylketonuria (PKU) and galactosemia, a pediatric metabolic specialist and nutritionist are needed to educate parents regarding foods that are appropriate. Parents need to also be educated regarding monitoring the levels of certain compounds in the blood and urine to ensure that the infant is not harmed by the disease.
What diseases are newborns screened for?
What diseases are screened for depends on the state where you live. In most states, testing is done for phenylketonuria (PKU), hypothyroidism, galactosemia, and sickle cell anemia (SC)/other hemoglobin disorders.
- Phenylketonuria (PKU). PKU is a recessive disorder which occurs in about one in 10,000 to 15,000 live births and is caused by a deficiency of the enzyme phenylalanine hydroxylase. This enzyme normally converts phenylalanine (present in dietary protein) to tyrosine. Infants with PKU may be asymptomatic for many weeks. However, over time, they can display delays in development, small head size, intellectual disability, seizures, hyperactivity, and a decreased growth rate. Dietary restriction of phenylalanine is needed to treat PKU and should begin as soon as possible after birth and continued throughout the life of an individual with PKU. If left untreated, most persons with PKU have an IQ less than 50.
- Congenital hypothyroidism. Congenital hypothyroidism is a condition in which there is an inadequate production of the thyroid hormone, seen in one in 3,000 to 4,000 live births. The cause is usually total or partial failure of the thyroid gland to develop, or its development is in an abnormal location. Infants with hypothyroidism can appear normal for the first several months of life. Clinical signs that can develop include jaundice, constipation, poor muscle tone, feeding problems, lethargy, a puffy face, large tongue, umbilical hernia, and hypothermia. If untreated, severe intellectual disability, growth delays, deafness, and other neurological abnormalities can occur. To treat congenital hypothyroidism, synthetic thyroid hormone is given daily, in most cases. The thyroid is evaluated periodically by blood tests and evaluation of the baby's growth and development.
- Galactosemia. Galactosemia is a recessive disorder that occurs in about one in every 30,000 to 60,000 live births and is caused by a deficiency in one of three enzymes that are responsible for metabolizing galactose. Galactose is a component of lactose, found in human and other animal milk. Infants with galactosemia may be asymptomatic for many months; however, within a few days to a few weeks after milk feeding is initiated, the clinical features often begin to develop. They include vomiting, diarrhea, lethargy, failure to thrive, jaundice, cataracts (depending on the enzyme deficiency), hypoglycemia, and sepsis (infection). Without rapid diagnosis and treatment, death can result. If the infant survives the neonatal period but continues untreated, progressive intellectual and physical disabilities, growth failure, cataracts, and enlarged liver may result. Dietary restriction of galactose and lactose is needed to treat galactosemia and should begin as soon as possible after birth and continued throughout the life of an individual with galactosemia.
- Sickle cell anemia. Sickle cell anemia is one of the most common, inherited single gene disorders in African-Americans. About one in 400 African-American babies is born with sickle cell anemia, and about one in 12 African-American people carries the gene for sickle cell anemia. Sickle cell disease involves the red blood cells, or hemoglobin, and their ability to carry oxygen. Normal hemoglobin cells are smooth, round, and flexible, like the letter "O," so they can move through the vessels in our bodies easily. Sickle cell hemoglobin cells are stiff and sticky, and form into the shape of a sickle, or the letter "C" when they lose their oxygen. These sickle cells tend to cluster together and cannot easily move through the blood vessels. The cluster causes a blockage and stops the movement of healthy, normal oxygen carrying blood. This blockage is what causes the painful and damaging complications of sickle cell disease. Sickle cells only live for about 15 days, whereas normal hemoglobin cells can live up to 120 days. Also, sickle cells risk being destroyed by the spleen because of their shape and stiffness. The spleen is an organ that helps filter the blood of infections. Sickled cells get "stuck" in this filter and die. Due to the decreased number of hemoglobin cells circulating in the body, a person with sickle cell is chronically anemic. The spleen also suffers damage from the sickled cells blocking healthy oxygen carrying cells. After repeated blockages, the spleen is very small and does not work properly. Without a functioning spleen, these individuals are more at risk for infections. Infants and young children are at risk for life-threatening infections. Treatment includes prompt emergency care for fevers and infections, appropriate vaccinations, penicillin, and management of anemia.
Division Chief, Genetics and Metabolism
Director, Rare Disease Institute
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