Every state and U.S. territory routinely screens newborns for certain genetic, metabolic, hormonal and functional disorders. Most of these birth defects have no immediate visible effects on a baby but, unless detected and treated early, can cause physical problems, mental retardation and, in some cases, death.
Except for hearing screening, all newborn screening tests are done using a few drops of blood from the newborn's heel. Fortunately, most babies are given a clean bill of health when tested. However, in 2002, about 3,300 babies were found to have metabolic disorders and another 12,000 to 16,000 to have hearing impairment (1, 2). In these cases, early diagnosis and proper treatment can make the difference between healthy development and lifelong impairment.
Which newborn screening tests are most likely to be given to my baby?
This depends on where your baby is born. Currently each state or region operates by law its own newborn screening program. Individual programs vary widely in the number and types of conditions for which they test. Some states test for as few as four disorders, while others test for 30 or more (3).
You can find out which tests are routinely done in your state by asking your health care provider or state health department. You can also visit the National Newborn Screening and Genetics Resource Center Web site. This site also lists commercial and nonprofit laboratories that provide comprehensive newborn screening for parents considering having their baby tested for more disorders than those screened for by their state.
All states and U.S. territories screen newborns for phenylketonuria (PKU), hypothyroidism and galactosemia (3). The test for PKU was the nation's first newborn screening test. Developed with the help of the March of Dimes, it has been routinely administered since the 1960s. PKU affects about 1 baby in 25,000 (4). Babies with the disorder cannot process a part of protein called phenylalanine, which is found in nearly all foods. Without treatment, phenylalanine builds up in the blood stream and causes brain damage and mental retardation.
When PKU is detected early, mental retardation can be prevented by feeding the baby a special formula that is low in phenylalanine. This low-phenylalanine diet will need to be followed throughout childhood, adolescence, and generally, for life.
Women of childbearing age with PKU need to remain on this special diet before and during pregnancy. This will often prevent mental retardation in their children by avoiding fetal exposure to high maternal phenylalanine levels (5).
Congenital hypothyroidism is the most common disorder identified by routine screening. It affects at least 1 baby in 5,000 (4). Congenital hypothyroidism is a thyroid hormone deficiency that retards growth and brain development. If it is detected in time, a baby can be treated with oral doses of thyroid hormone to permit normal development.
Galactosemia, which affects about 1 baby in 50,000, can cause death in infancy, or blindness and mental retardation (4). A baby with galactosemia is unable to convert galactose, a sugar in milk, into glucose, a sugar the body uses as an energy source. The treatment for galactosemia is to eliminate milk and all other dairy products from the baby's diet; this dietary restriction is lifelong (5).
Almost all states also screen for sickle cell anemia, congenital adrenal hyperplasia (CAH) and hearing loss. Sickle cell anemia is an inherited blood disease that can cause bouts of pain, damage to vital organs and, sometimes, death in childhood. Young children with sickle cell anemia are especially prone to dangerous bacterial infections such as pneumonia and meningitis. Vigilant medical care and early treatment with penicillin, beginning in infancy, can dramatically reduce these serious complications and the deaths that can result from them. Sickle cell anemia affects about 1 in 400 African-American babies (1) and at least 1 in 5,000 of all babies in the United States (4).
CAH is a group of disorders in which there is a deficiency of certain hormones, sometimes affecting genital development. In severe cases, CAH also can cause life-threatening salt loss from the body. Lifelong treatment with the missing hormones suppresses this disease, which occurs in about 1 in 25,000 babies (4).
Up to 3 to 4 in 1,000 newborns have significant hearing impairment (2). Without testing, most babies with hearing loss are not diagnosed until 2 or 3 years of age (2). By this time, they often have delayed speech and language development. Detection of hearing loss in the neonatal period allows the baby to be fitted with hearing aids before 6 months of age, helping prevent serious speech and language problems.
The National Center for Hearing Assessment and Management provides resources for both health care providers and families. The center has produced a 6-minute educational video for parents "Giving Your Baby a Sound Beginning," which is available in English and Spanish. The video may be viewed online at no charge, or a VHS copy may be purchased for $15.
What other disorders can newborn screening detect?
Recent advances in technology, such as tandem mass spectrometry, now make it possible to screen for about 55 disorders. The March of Dimes would like to see all babies in all states screened for at least 29 specific disorders, for which effective treatment is available. This March of Dimes recommendation is based on endorsement of a report by the American College of Medical Genetics (commissioned by the Health Resources and Services Administration) urging screening for the 29 disorders (4), and will be updated when appropriate. (In addition to these 29 disorders, the March of Dimes recommends that states report screening results of 25 “secondary target” conditions. However, treatment for these additional disorders is generally not yet available.)
Treatment for the 29 disorders is likely to improve the health of children who are affected by them. The disorders are grouped into five categories:
Organic acid metabolism disorders: Each disease in this group of inherited disorders results from the loss of activity of an enzyme involved in the breakdown of amino acids, the building blocks of proteins, and other substances (lipids, sugars, steroids). When any of these chemicals is not properly broken down, toxic acids build up in the body. Without treatment, these disorders can result in coma and death during the first month of life.- IVA (isovaleric acidemia)
- GA I (glutaric acidemia)
- HMG (3-OH 3-CH3 glutaric aciduria)
- MCD (multiple carboxylase deficiency)
- MUT (methylmalonic acidemia due to mutase deficiency)
- Cbl A,B (methylmalonic acidemia)
- 3MCC (3-methylcrotonyl-CoA carboxylase deficiency)
- PROP (propionic acidemia)
- BKT (beta-ketothiolase deficiency)
- MCAD (medium-chain acyl-CoA dehydrogenase deficiency)
- VLCAD (very long-chain acyl-CoA dehydrogenase deficiency)
- LCHAD (long-chain L-3-OH acyl-CoA dehydrogenase deficiency)
- TFP (trifunctional protein deficiency)
- CUD (carnitine uptake defect)
Amino acid metabolism disorders: This is a diverse group of disorders with varying degrees of severity. Some individuals lack enzymes that are needed to break down the building blocks of protein called amino acids. Others have deficiencies in enzymes that help the body rid itself of the nitrogen incorporated in amino acid molecules. Toxic levels of amino acids or ammonia can build up in the body causing a variety of signs and symptoms, and even death.
- PKU (phenylketonuria)
- MSUD (maple syrup urine disease)
- HCY (homocystinuria due to CBS deficiency)
- CIT (citrullinemia)
- ASA (argininosuccinic acidemia)
- TYR I (tyrosinemia type I)
Hemoglobinopathies: These inherited diseases of red blood cells result in varying degrees of anemia (shortage of red blood cells) and other health problems. The severity of these disorders varies greatly from one person to the next.
- Hb SS (sickle cell anemia)
- Hb S/Th (hemoglobin S/beta-thalassemia)
- Hb S/C (hemoglobin S/C disease)
Others: This mixed group of disorders includes some diseases that are inherited and others that are not. This group of disorders varies greatly in severity, from mild to life threatening.
- CH (congenital hypothyroidism)
- BIOT (biotinidase deficiency)
- CAH (congenital adrenal hyperplasia due to 21-hydroxylase deficiency)
- GALT (classical galactosemia)
- HEAR (hearing loss)
- CF (cystic fibrosis)
All of these disorders, except for hearing loss, are detected by a blood test. The baby's heel is pricked to obtain a few drops of blood for laboratory analysis. The same blood sample can be used to screen for 55 or more disorders. Usually, the baby's blood specimen is sent to a state public health laboratory for testing, and findings are sent to the health care professional responsible for the infant's care. Babies are screened for hearing loss with one of two tests that measure how the baby responds to sounds. These tests are done in the newborn hospital nursery, using either a tiny soft earphone or microphone that is placed in the baby's ear. If either of these tests shows abnormal results, the baby needs more extensive hearing testing to see if he does have hearing loss.
How soon after birth should screening tests be done?
A blood specimen should be taken from every newborn before hospital release, usually at 24 to 48 hours of life. Some of the tests (such as the one for PKU) may not give accurate results, however, if they are done too soon after birth. Because of early hospital discharge, some babies are tested within the first 24 hours of life. Because some cases of PKU can be missed when the test is performed this early, the American Academy of Pediatrics recommends that a repeat specimen be taken 1 to 2 weeks later from infants whose initial test was taken within the first 24 hours of life (6). Some states routinely screen twice in the newborn nursery and again approximately two weeks later. Hearing tests are usually performed before the baby is discharged from the hospital. Babies born outside the hospital should have newborn screening tests done before the seventh day of life (6).
What does an abnormal test result mean?
Parents should not be overly alarmed by abnormal test results, as the initial screening tests give only preliminary information that must be immediately followed by more precise testing. Most babies with abnormal thyroid screening test results, for example, prove normal in further testing, as do most with abnormal hearing test results (6, 7).
What should I do if my child is diagnosed with one of the conditions for which he was tested?
Your child may need follow-up treatment at a pediatric center that specializes in children with metabolic or genetic conditions. It is essential for your child's healthy development that you follow the health care provider's treatment recommendations. As your child grows, he or she may need careful, continued evaluations and monitoring.
If one of my children has a disorder, will my other children have it?
For most of the disorders detected by newborn screening, when one child in a family is affected, the chance of the same birth defect occurring in a sibling is 1 in 4. The chances remain the same with each pregnancy. Parents who have a baby with one of these disorders can discuss their risk of having another affected child with their health care provider or a genetic counselor. These disorders are inherited when both parents have the same abnormal gene and pass it on to their baby. A parent who has the abnormal gene, but not the disease, is called a carrier. The health of a carrier is rarely affected.
Congenital hypothyroidism usually is not inherited from parents (6). The siblings of those who have this disorder are seldom affected.
Hearing loss can be passed on through parents' genes. However, other causes of hearing loss, such as infections that are passed on to the baby during pregnancy or birth, are unlikely to recur in another pregnancy.
Does the March of Dimes fund research on newborn screening?
The March of Dimes has long supported research related to newborn screening. In the 1960s, a March of Dimes grantee developed the first PKU screening test. Other grantees developed screening tests for biotinidase deficiency and congenital adrenal hyperplasia and contributed to the development of testing for hypothyroidism. The March of Dimes also funds research aimed at improving the treatment of children with a number of the screened disorders, and for many years, has worked to expand and improve newborn screening programs.
References
1. General Accounting Office. Newborn Screening: Characteristics of State Programs. Washington, DC: U.S. General Accounting Office, 2003. Publication GAO-03-449. Data from the National Newborn Screening and Genetics Resource Center.
2. National Center for Hearing Assessment and Management, Utah State University, accessed 9/28/04.
3. National Newborn Screening and Genetics Resources Center. U.S. National Screening Status Report. Updated 9/8/04.
4. American College of Medical Genetics. Newborn Screening: Toward a Uniform Screening Panel and System. Final Report, March 8, 2005.
5. Tuerck, J., et al. The Northwest Regional Newborn Screening Program Oregon Practitioner's Manual, 7th edition. Oregon Health & Science University and Oregon Department of Human Services, 2004.
6. American Academy of Pediatrics Committee on Genetics. Newborn Screening Fact Sheets. Pediatrics, volume 98, number 3, September 1996.
7. American Academy of Pediatrics. Hearing: Understanding Screening Results. Accessed 9/30/04.
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