(Study type: Blood [see individual studies for specimen requirements]; related body system: Circulatory/Hematopoietic, Endocrine, Digestive, Immune, Nervous, and Reproductive systems.)

Newborn screening is a process used to evaluate infants for disorders that are treatable but difficult to identify by direct observation of diagnosable symptoms. The testing is conducted shortly after birth through a collaborative effort between government agencies, local public health departments, hospitals, and parents. Knowledge of genetics assists in identifying those who may benefit from additional education, risk assessment, and counseling. Genetics is the study and identification of genes, genetic sequence variations, and inheritance. For example, genetics provides some insight into the likelihood of inheriting a medical condition such as cystic fibrosis (CF), an aminoacidopathy, or a hemoglobinopathy. Some conditions are the result of sequence variations involving a single gene, whereas other conditions may involve multiple genes and/or multiple chromosomes. Sickle cell disease is an example of an autosomal recessive disorder in which the offspring inherits a copy of the defective gene from each parent. Further information regarding inheritance of genes can be found in the study titled “Genetic Testing.”

Hearing Screening

Every state and territory in the United States has a newborn screening program (mandated or voluntary) that includes early hearing loss detection and intervention (EHDI). The goal of EHDI is to ensure that permanent hearing loss is identified before 3 mo of age, appropriate and timely intervention services are provided before 6 mo of age, families of infants with hearing loss receive culturally competent support, and tracking and data management systems for newborn hearing screens are linked with other relevant public health information systems. For more detailed information, refer to the study titled “Audiometry, Hearing Loss.” Testing of interest that is not included in the mandatory list can be requested by a health-care provider (HCP), as appropriate. Confirmatory testing is performed if abnormal findings are produced by screening methods. Properly collected blood spot cards contain sufficient sample to perform both screening and confirmatory testing. Confirmatory testing varies depending on the initial screen and can include fatty acid oxidation probe tests on skin samples, enzyme uptake testing of skin or muscle tissue samples, enzyme assays of blood samples, DNA testing, gas chromatography/mass spectrometry, and tandem mass spectrometry. Testing for common genetically transferred conditions can be performed on either or both prospective parents by blood tests, skin tests, or DNA testing. DNA testing can also be performed on the fetus, in utero, through the collection of fetal cells by amniocentesis or chorionic villus sampling. Counseling and written, informed consent are recommended and sometimes required before genetic testing.

Heart Screening

Newborn screening for congenital heart defects is a noninvasive test done at the bedside with a pulse oximeter. The seven most common critical heart defects detected by pulse oximetry include the following:

• hypoplastic left heart syndrome
• pulmonary atresia
• tetralogy of Fallot
• total anomalous pulmonary venous return
• transposition of the great arteries
• tricuspid atresia
• truncus arteriosus

Endocrine Disorders

Inadequate production of the thyroid hormone thyroxine can result in congenital hypothyroidism, which when untreated manifests in severely delayed physical and intellectual development. Inadequate production may be due to a defect such as a missing, misplaced, or malfunctioning thyroid gland. Inadequate production may also be due to the biological mother’s thyroid condition or treatment during pregnancy or, less commonly encountered in developed nations, a biological mother’s deficiency of iodine. Most newborns do not exhibit signs and symptoms of thyroxine deficiency during the first few weeks of life while they function on the hormone provided by their biological mother. As the biological mother’s thyroxine is metabolized, some of the symptoms that ensue include coarse, swollen facial features; wide, short hands; respiratory problems; a hoarse-sounding cry; poor weight gain and small stature; delayed occurrence of developmental milestones such as sitting up, crawling, walking, and talking; goiter; anemia; bradycardia; myxedema (accumulation of fluid under the skin); and hearing loss. Children who remain untreated usually demonstrate physical and intellectual disabilities. They may have an unsteady gait and lack coordination. Most demonstrate delays in development of speech, and some have behavioral problems.

The adrenal glands are responsible for production of the hormones cortisol, aldosterone, and male sex androgens. Most infants born with congenital adrenal hyperplasia (CAH) make too much of the androgen hormones and not enough cortisol or aldosterone. The complex feedback loops in the body call for the adrenal glands to increase production of cortisol and aldosterone, and as the adrenal glands work harder to increase production, they increase in size, resulting in hyperplasia. CAH is a group of conditions. Most frequently, lack of or dysfunction of an enzyme called 21-hydroxylase results in one of two types of CAH. The first is a salt-wasting condition in which insufficient levels of aldosterone cause too much salt and water to be lost in the urine. Newborns with this condition are poor feeders and appear lethargic or sleepy. Other symptoms include vomiting, diarrhea, and dehydration, which can lead to weight loss, low blood pressure, and decreased electrolytes. If untreated, these symptoms can result in metabolic acidosis and shock, which in infants with CAH is called an adrenal crisis. Signs of an adrenal crisis include confusion, irritability, tachycardia, and coma. The second most common type of CAH is a condition in which having too much of the androgen hormones in the blood causes female babies to develop masculinized or virilized genitals. High levels of androgens lead to precocious sexual development, well before the normal age of puberty, in both boys and girls.

Abnormal Hemoglobins

Hemoglobin (Hgb) A is the main form of Hgb in the healthy adult. Hgb F is the main form of Hgb in the fetus, the remainder being composed of Hgb A₁ and A₂. Hgb S and C result from abnormal amino acid substitutions during the formation of Hgb and are inherited hemoglobinopathies. Hgb S results from an amino acid substitution during Hgb synthesis, whereby valine replaces glutamic acid. Hgb C Harlem results from the substitution of lysine for glutamic acid. Hgb electrophoresis is a separation process used to identify normal and abnormal forms of Hgb. Electrophoresis and high-performance liquid chromatography as well as molecular genetics testing for sequence variations can also be used to identify abnormal forms of Hgb. Individuals with sickle cell disease have chronic anemia because the abnormal Hgb is unable to carry oxygen. The red blood cells of affected individuals are also abnormal in shape, resembling a crescent or sickle rather than the normal disk shape. This abnormality, combined with cell-wall rigidity, prevents the cells from passing through smaller blood vessels. Blockages in blood vessels result in hypoxia, damage, and pain. Individuals with the sickle cell trait do not have the clinical manifestations of the disease but may pass the disease on to children if the other parent has the trait (or the disease) as well.

In addition to newborn screening, preconception (both biological parents) and prenatal hemoglobin electrophoresis screening have also become routine practice, especially in ethnic populations with a high prevalence for sickle cell anemia, sickle cell disease, and thalassemia in order to detect abnormal hemoglobins. Repeat hemoglobin electrophoresis testing in patients with a known hemoglobinopathy is unnecessary unless it is needed to make a more specific diagnosis or to monitor therapeutic effectiveness.

Disorders of Amino Acid Metabolism

Amino acids are required for the production of proteins, enzymes, coenzymes, hormones, nucleic acids used to form DNA, pigments such as Hgb, and neurotransmitters. Testing for specific aminoacidopathies is generally performed on infants after an initial screening test with abnormal results. Certain inherited enzyme deficiencies interfere with normal amino acid metabolism and cause excessive accumulation of or deficiencies in amino acid levels. The major genetic disorders include PKU, MSUD, and tyrosinuria. Enzyme disorders can also result in conditions of dysfunctional fatty acid or organic acid metabolism in which toxic substances accumulate in the body and, if untreated, can result in death. Infants with these conditions often appear normal and healthy at birth. Symptoms can appear soon after feeding begins or not until the first months of life, depending on the specific condition. Most of the signs and symptoms of amino acid disorders in infants include poor feeding, lethargy, vomiting, and irritability. Newborns with MSUD produce urine that smells like maple syrup or burned sugar. Accumulation of ammonia, a by-product of protein metabolism, and the corresponding amino acids results in progressive liver damage, hepatomegaly, jaundice, and tendency to bruise and bleed. If untreated, there may be delays in growth, lack of coordination, and permanent learning and intellectual disabilities. Early diagnosis and treatment of certain aminoacidopathies can prevent intellectual disabilities, reduced growth rates, and various unexplained symptoms.

Infectious Disease Testing

HIV is the cause of AIDS and is transmitted through bodily secretions, especially by blood or sexual contact. The virus preferentially binds to the T4 helper lymphocytes and replicates within the cells. Current assays detect several viral proteins. Positive results should be confirmed by Western blot assay. This test is routinely recommended as part of a prenatal work-up and is required for evaluating donated blood units before release for transfusion. The Centers for Disease Control and Prevention (CDC) structured its recommendations to increase identification of HIV-infected patients as early as possible; early identification increases treatment options, increases frequency of successful treatment, and can decrease further spread of disease.

Other Significant Inherited Disorders

CF is a genetic disease that affects normal functioning of the exocrine glands, causing them to excrete large amounts of electrolytes. CF is characterized by abnormal exocrine secretions within the lungs, pancreas, small intestine, bile ducts, and skin. Some of the signs and symptoms that may be demonstrated by the newborn with CF include failure to thrive, salty sweat, chronic respiratory problems (constant coughing or wheezing, thick mucus, recurrent lung and sinus infections, nasal polyps), and chronic gastrointestinal problems (diarrhea, constipation, pain, gas, and greasy, malodorous stools that are bulky and pale colored). Patients with CF have sweat electrolyte levels two to five times normal. Sweat test values, with family history and signs and symptoms, are required to establish a diagnosis of CF. Clinical presentation may include chronic problems of the gastrointestinal and/or respiratory system. CF is more common in people of European descent than in other populations. Testing of stool samples for decreased trypsin activity has been used as a screen for CF in infants and children, but this is a much less reliable method than the sweat test. Sweat conductivity is a screening method that estimates chloride levels. Sweat conductivity values greater than or equal to 50 mEq/L should be referred for quantitative analysis of sweat chloride. The sweat electrolyte test is still considered the gold standard diagnostic for CF.

Biotin is an important water-soluble vitamin/cofactor that aids in the metabolism of fats, carbohydrates, and proteins. A hereditary enzyme deficiency of biotinidase prevents biotin released during normal cellular turnover or via digested dietary proteins from being properly recycled and absorbed, resulting in biotin deficiency. Signs and symptoms of biotin deficiency appear within the first few months and can result in hypotonia, poor coordination, respiratory problems, delays in development, seizures, behavioral disorders, and learning disabilities. Untreated, the deficiency can lead to loss of vision and hearing, ataxia, skin rashes, and hair loss.

Lactose, the main sugar in milk and milk products, is composed of galactose and glucose. Galactosemia occurs when there is a deficiency of the enzyme galactose-1-phosphate uridyl transferase, which is responsible for the conversion of galactose into glucose. The inability of dietary galactose and lactose to be metabolized results in the accumulation of galactose-1-phosphate, which causes damage to the liver, central nervous system, and other body systems. Newborns with galactosemia usually have diarrhea and vomiting within a few days of drinking milk or formula containing lactose. Other early symptoms include poor feeding, failure to gain weight or grow in length, lethargy, and irritability. The accumulation of galactose-1-phosphate and ammonia is damaging to the liver, and symptoms likely to follow if untreated include hypoglycemia, seizures, coma, hepatomegaly, jaundice, bleeding, shock, and life-threatening bacteremia or septicemia. Early cataracts can occur in about 10% of children with galactosemia. Most untreated children eventually die of liver failure.

Testing for other rare but potentially life-threatening conditions may also be considered for the following:

• galactosemia
• mucopolysaccharidosis type I
• Pompe disease (glycogen storage disease type II)
• severe combined immunodeficiency
• spinal muscular atrophy
• X-linked adrenoleukodystrophy

Rare Conditions

Inborn errors of amino acid metabolism

• Tyrosinemia type

Inborn errors of fatty acid metabolism

• Carnitine uptake disorder
• Long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency
• Trifunctional protein (TFP) deficiency
• Very-long-chain acyl-CoA dehydrogenase deficiency

Inborn errors of organic acid metabolism

• 3-Hydroxy, 3-methylglutaric aciduria
• Beta ketothiolase
• Isovaleric acidemia
• Methyl malonic acidemias (vitamin B₁₂ disorders)
• Multiple carboxylase (holocarboxylase)
• Propionic acidemia

Other multisystem diseases

• Biotinidase deficiency