The availability of newborn screening tests has made early diagnosis of many metabolic disorders possible. The good news: With early diagnosis can come early treatment and, for many babies who might otherwise have died within a few months of birth, the chance to live a completely normal life. Conditions that can be diagnosed and treated include:
Congenital hypothyroidism, which results from an inadequate supply of thyroid hormone and affects 1 baby in 4,000. Oral doses of thyroid medication prevent the stunted growth and mental retardation associated with hypothyroidism.
Congenital adrenal hyperplasia, a condition in which hormone deficiency compromises genital development and kidney function, affects 1 in 5,000 babies, and can be treated with
hormone replacement.
Medium chain acyl-coA dehydrogenase deficiency (MCAD) results when the enzyme
needed to convert food fat to energy is missing. It affects 1 in 15,000 babies and can lead to severe metabolic problems with otherwise simple illnesses. Since the condition shows up only during prolonged fasting (as might occur if appetite is lost to a virus or other illness), the treatment involves feeding on a regular schedule.
Galactosemia, in which 1 in 50,000 affected babies can’t convert galactose, a milk sugar, into glucose (eventually causing mental retardation and liver disease), can be treated with the elimination of dairy products.
Biotinidase deficiency, which occurs in 1 in 70,000 babies, results from the deficiency of biotinidase, an enzyme that recycles biotin (one of the B vitamins). Without treatment (supplementation with biotin), it can cause frequent infections, poor muscle control, seizures, hearing loss, and mental retardation.
Maple syrup urine disease (MSUD), which affects 1 in 250,000 babies, occurs when the body is unable to use some components of food protein, and can result in poor feeding, lethargy, and, eventually, coma. Given its name because an affected baby’s urine smells like maple syrup, MSUD can be treated with a special diet.
Homocystinuria affects 1 in 250,000 infants and is due to a lack of enzymes in the liver.
Untreated, it can lead to skeletal abnormalities, abnormal blood clotting, mental
retardation, and eye problems. A special diet, combined with dietary supplements, can prevent these symptoms.
Phenylketonuria (PKU), a condition in which the individual is unable to metabolize an amino acid (or “protein building block”) called phenylalanine, affects 1 in 12,000 infants.
If left untreated, the buildup of phenylalanine in the bloodstream can interfere with brain development and cause severe retardation. A diet low in phenylalanine (low in high- protein foods such as breast milk, cow’s milk, or regular cow’s milk formula and meat), begun immediately and continued indefinitely, will allow a child with PKU to live a normal life.
How common is it? Much less common since the development of preventive techniques; still, about 7,000 infants a year are affected in the United States.
Who is susceptible? A baby who inherits Rh-positive blood from his or her father and has a mother with Rh-negative blood.
What causes it? Antibodies in mother’s blood attack baby’s blood cells, recognizing them as foreign.
Related problems. Severe anemia and jaundice, leading to possible brain damage, or death before or
shortly after birth.
Treatment. Often a complete blood transfusion of the baby’s blood (an “exchange transfusion”).
Some babies may not need a transfusion immediately but do require one at four to six weeks because of severe anemia. Prevention, with the injection of a vaccine called Rh immune globulin for Rh- negative mothers within seventy-two hours of the birth (or miscarriage or abortion) of a baby or fetus that is Rh-positive is the best way to prevent the problem in future pregnancies. A dose of the vaccine may also be given about midway during pregnancy.
Prognosis. Usually good, with treatment.
SICKLE-CELL ANEMIA
What is it? An anemia in which red blood cells (usually round) are abnormal (sickle shaped) and do a poor job of carrying oxygen to body cells, often getting stuck in and blocking blood vessels.
Symptoms (such as fatigue, shortness of breath, joint swelling, especially in fingers and toes, and severe bone pain) don’t usually appear until six months of age, but testing should diagnose the condition immediately after birth.
How common is it? Affects 1 in 400 African American children; lower incidence in others.
Who is susceptible? Primarily blacks of African descent, but also whites of Mediterranean/Middle Eastern heritage. Risk is 1 in 4 if both parents are carriers, 4 in 4 if both have the disease.
What causes it? Autosomal recessive inheritance: Both parents must pass on recessive genes for child to be affected. Periodic crises can be triggered by infection, stress, dehydration, and inadequate oxygen.
Related problems. Poor growth, delayed puberty, narrow body, curved spine and barrel chest;
infection, particularly pneumococcal. It can be fatal if untreated.
Treatment. Penicillin daily beginning at two months, at least through age five. Also symptomatic relief: pain relievers, blood transfusions, oxygen, fluids. Full series of immunizations, including pneumococcal vaccine. Parent education and genetic counseling are also important.
Prognosis. Fair. Still, most live past young adulthood, and some reach middle age and beyond.
Treatment greatly improves prognosis. Promising research is being done into new and better treatments.
SPINA BIFIDA (OPEN SPINE)
What is it? The bony spine, or backbone, that helps protect the spinal cord is normally open for the first few days of prenatal development but then closes. In spina bifida, the closing is incomplete. The resultant opening can be so slight that it causes no problems and is not noticed except through an X ray taken later for other reasons, though a small dimple or tufts of hair may be visible on the covering skin. Or it can be large enough that part of the covering of the spinal cord protrudes through, covered by a purplish red cyst or lump (a meningocele), which can range in size from an inch or two in
diameter to the size of a grapefruit. If this meningocele is low on the spinal column, it can cause weakness in the legs. In the most severe form of spina bifida, the spinal cord itself protrudes through the opening. It often has little or no skin protecting it, allowing spinal fluid to leak out. The area is often covered with sores, the legs are paralyzed, and bladder and bowel control become a problem later, though some children do attain this control.
How common is it? Affects 1 in 2,000 babies born in the United States, though it has been estimated that 1 in 4 may have hidden spina bifida. The more severe form of the condition is fortunately the least common. There has been a nearly 20 percent reduction in the number of babies born with neural tube defects such as spina bifida in recent years. This can be attributed to the use of folic acid
supplements by mothers before conception and through the first two months of pregnancy, as well as the fortification of breads and cereals with folic acid.
Who is susceptible? Children of mothers who already have an affected child have a 1 in 40 risk; with two affected children in the family, the risk rises to 1 in 5. Cousins of affected children have a
twofold increase in risk.
What causes it? Not known at present. Heredity is probably involved in some way along with adverse prenatal environment. Nutrition may be involved—specifically a low intake of folic acid.
Related problems. Infection when spine is visibly open. Also hydrocephalus in about 70 to 90 percent of cases (see page 645). Lower limb paralysis and numbness, impaired bladder and bowel control.
Treatment. None is needed for a slight defect. Cysts can be removed surgically and hydrocephalus can be shunted. But though surgery can remove the most severe cysts and repair the opening, covering it with muscle and skin, the paralysis in the legs can’t be cured. Physical therapy, and later leg braces and crutches or a wheelchair, will probably be needed. Casts may be applied to prevent or minimize deformity. Prior to surgery, it is important not to put pressure (even in the form of clothing) on the cyst. Team approach to treatment, with a range of specialists, is usually best. Spina bifida can often be detected through prenatal testing, such as blood tests, ultrasound, and amniocentesis. Prenatal surgery to repair spina bifida birth defects is in the experimental phase.
Prognosis. Depends on the severity of the condition. Most children with less severe conditions can have active and productive lives; most females will be able to bear children, but their pregnancies will be in the high-risk category.
TAY-SACHS DISEASE
What is it? Children with this lipid-storage disease, in which there is a congenital deficiency of an enzyme needed for breaking down fatty deposits in the brain and nerve cells, appear normal at birth.
But about six months later, when the fatty deposits begin to clog cells, the nervous system stops
working and children begin to regress—they stop smiling, crawling, and turning over, lose the ability to grasp, gradually become blind, paralyzed, and unaware of their surroundings. Most die by age three or four.