Newborn Screening Uncovers Hidden Genetic Disorders
How can a seemingly healthy newborn have a genetic disorder?
Kimberly Chapman, MD, PhD, Section Chief, Medical Genetics at Children’s Hospital Los Angeles explains how newborn screening works, and how it can prevent lifelong disability—and could even save a child’s life.
What is a newborn screening and why do we do it?
Dr. Chapman: Newborn screening has been around since 1966, and it is done by every state. Within 24-48 hours after birth, every baby in California has a few drops of blood drawn from their heel before leaving the hospital. This simple “blood spot” test screens for certain genetic disorders—conditions caused by an absent or defective gene or by a chromosomal aberration. These conditions can cause health problems. Some can even be fatal without treatment. But they typically aren’t apparent at birth. Testing can uncover them before any symptoms arise.
Why is newborn screening before symptoms appear important?
Dr. Chapman: By the time symptoms appear, it can be too late. In the past, some of these children would die suddenly. Others suffered severe mental disability. A good example is phenylketonuria (PKU). Babies with PKU look like every other baby, but they lack the enzyme that processes a certain amino acid. This amino acid then builds up in the child’s blood over time and causes irreversible brain damage. But if we can test babies before any symptoms appear, and find the infant has PKU, we can put the child on a special diet from birth and help prevent the intellectual disability that occurs without treatment. Early screening can make the difference between a relatively healthy life and severe mental disability.
For what conditions are babies screened?
Dr. Chapman: California screens all newborns for hearing loss and more than 80 disorders. These include certain congenital heart conditions; severe combined immunodeficiency (SCID), where a baby lacks a functional immune system; and spinal muscular atrophy (SMA), which is a cluster of neuromuscular disorders; cystic fibrosis, a disorder that affects the lungs; and sickle cell disease.
How do conditions get included in the newborn screening list?
Dr. Chapman: For a condition to be added to the newborn screen, it must meet two criteria: it must show up early, and an effective treatment must exist—not necessarily to cure the disorder, but to make it milder.
What should parents do if their baby screens positive for something?
Dr. Chapman: The most important thing is to listen to the doctor’s instructions and follow them. It’s critical to do follow-up testing to find out more. About 1 in 600 infants in California test positive for a genetic condition on the newborn screening. If your baby’s test results are abnormal—remember, this is a screening test, not a diagnostic test—they will be referred for confirmatory testing. California pays for confirmatory testing, which could include blood, urine, or genetic testing, depending on the diagnosis.
When does CHLA get involved?
Dr. Chapman: At CHLA, we don’t do the screening, but we provide treatment and genetic counseling to families whose babies test positive for a genetic condition. I specialize in metabolic disorders, so when a baby screens positive for one of those disorders, pediatricians often refer the child to me.
Do we only screen for disorders we can cure?
Dr. Chapman: Currently there is no permanent cure for these genetic conditions. But pharmaceutical and dietary measures are available to manage them—often very successfully. For metabolic disorders, the treatment is usually a special diet and/or vitamin supplements. When started early, these treatments can enable children to live normal or near-normal lives. For example, some babies are missing an enzyme that recycles biotin, a B-complex vitamin, in the body. Lack of this enzyme can cause seizures, hearing loss, vision loss, and developmental delays. But if we can identify them at birth, we can treat them with a daily dose of biotin. After treatment, most of them will go on to lead healthy lives.
Treatment is changing fast as we learn more and new research is conducted. How accurate is the screening?
Dr. Chapman: Newborn screening is designed to pick up every infant with the disorder. The test cut-offs are set up to be sensitive enough to pick up everybody with the disease, but there will be an overlap with individuals who will test positive for a condition but don't have it. When a screen is positive, we confirm the result with more testing.
What if parents don’t have a history of genetic disorders?
Dr. Chapman: Just because you don’t have the disorder doesn’t mean that you don’t carry a faulty copy of the gene for it. Most children with these disorders are born to parents with no family history of the condition. You can have something new in the patient that has not been seen in the family. Sometimes people have such a mild form of a disorder that they don’t even know they have it. More than a few times, we have diagnosed parents with a metabolic disorder after their baby screened positive.
How can CHLA help?
Dr. Chapman: We are here to work with you to give your child the best chance for a healthy life. We support parents through the journey from newborn screening and over the years as children grow. My most exciting milestone is when these kids graduate from high school and go on to college.
