出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/08/28 13:11:43」(JST)
| Newborn screening | |
|---|---|
| Intervention | |
| MeSH | D015997 |
Newborn screening is a public health program designed to screen infants shortly after birth for a list of conditions that are treatable, but not clinically evident in the newborn period. Some of the conditions included in newborn screening programs are only detectable after irreversible damage has been done, in some cases sudden death is the first manifestation of the disease. Screening programs are often run by state or national governing bodies with the goal of screening all infants born in the jurisdiction. The number of diseases screened for is set by each jurisdiction, and can vary greatly. Most newborn screening tests are done by measuring metabolites and enzyme activity in whole blood samples collected on specialized filter paper, however many areas are starting to screen infants for hearing loss using automated auditory brainstem response and congenital heart defects using pulse oximetry. Infants who screen positive undergo further testing to determine if they are truly affected with a disease or if the test result was a false positive. Follow-up testing is typically coordinated between geneticists and the infant's pediatrician or primary care physician.
Newborn screening debuted as a public health program in the United States in the early 1960s, and has expanded to countries around the world, with different testing menus in each country. The first disorder detected by modern newborn screening programs was phenylketonuria, a metabolic condition in which the inability to degrade the essential amino acid phenylalanine can cause irreversible mental retardation unless detected early. With early detection, and dietary management, the negative effects of the disease can be largely eliminated. Robert Guthrie developed a simple method using a bacterial inhibition assay that could detect high levels of phenylalanine in blood shortly after a baby was born. Guthrie also pioneered the collection of blood on filter paper which could be easily transported, recognizing the need for a simple system if the screening was going to be done on a large scale. Newborn screening around the world is still done using similar filter paper.
Robert Guthrie is given much of the credit for pioneering the earliest screening for phenylketonuria in the late 1960s using blood samples on filter paper obtained by pricking a newborn baby's heel on the second day of life to get a few drops of blood.[1] Congenital hypothyroidism was the second disease widely added in the 1970s.[2] Guthrie and colleagues also developed bacterial inhibition assays for the detection of maple syrup urine disease and classic galactosemia.[3] The development of tandem mass spectrometry screening in the early 1990s led to a large expansion of potentially detectable congenital metabolic diseases that can be identified by characteristic patterns of amino acids and acylcarnitines.[4]
In the United States, the American College of Medical Genetics recommended a uniform panel of diseases that all infants born in every state should be screened for. They also developed an evidence-based review process for the addition of conditions in the future. The implementation of this panel across the United States meant all babies born would be screened for the same number of conditions. Prior to this, babies born in different states had received different levels of screening. On April 24, 2008, President George W. Bush signed into law the Newborn Screening Saves Lives Act of 2007. This act was enacted to increase awareness among parents, health professionals, and the public on testing newborns to identify certain disorders. It also sought to improve, expand, and enhance current newborn screening programs at the state level.
Newborn screening programs initially used screening criteria based largely on criteria established by JMG Wilson and F. Jungner in 1968.[5] Although not specifically about newborn population screening programs, their publication, Principles and practice of screening for disease proposed ten criteria that screening programs should meet before being used as a public health measure. Newborn screening programs are administered in each jurisdiction, with additions and removals from the panel typically reviewed by a panel of experts. The four criteria from the publication that were relied upon when making decisions for early newborn screening programs were:
As diagnostic techniques have progressed, debates have arisen as to how screening programs should adapt. Tandem mass spectrometry has greatly expanded the potential number of diseases that can be detected, even without satisfying all of the other criteria used for making screening decisions.[6][7] Duchenne muscular dystrophy is a disease that has been added to screening programs in several jurisdictions around the world, despite the lack of evidence as to whether early detection improves the clinical outcome for a patient.[6]
Newborn screening tests are most commonly done from whole blood samples collected on specially designed filter paper. The filter paper is often attached to a form containing required information about the infant and parents. This includes date and time of birth, date and time of sample collection, the infant's weight and gestational age. The form will also have information about whether the baby has had a blood transfusion and any additional nutrition the baby may have received (total parenteral nutrition). Most newborn screening cards also include contact information for the infant's physician in cases where follow up screening or treatment is needed. The Canadian province of Quebec performs newborn screening on whole blood samples collected as in most other jurisdictions, and also runs a voluntary urine screening program where parents collect a sample at 21 days of age and submit it to a provincial laboratory for an additional panel of conditions.[8][9]
Newborn screening samples are collected from the infant between 24 hours and 7 days after birth, with the requirement that the baby has fed at least once. Samples can be collected at the hospital, or by midwives. If a sample is collected from an infant who is less than 24 hours old, the laboratory will often request a repeat specimen be taken after 24 hours. Samples are mailed daily to the laboratory responsible for testing. In the United States and Canada, newborn screening is mandatory, with an option for parents to opt out of the screening in writing if they desire.[10][11] In most of Europe, newborn screening is done with the consent of the parents. Proponents of mandatory screening claim that the test is for the benefit of the child, and that parents should not be able to opt out on their behalf. In regions that favour informed consent for the procedure, they report no increase in costs, no decrease in the number of children screened and no cases of included diseases in children who did not undergo screening.[12]
Because newborn screening programs test for a number of different conditions, a number of different laboratorial methodologies are used, as well as bedside testing for hearing loss using evoked auditory potentials[13] and congenital heart defects using pulse oximetry.[14] Newborn screening started out using simple bacterial inhibition assays to screen for a single disorder, starting with phenylketonuria in the early 1960s.[15] With this testing methodology, newborn screening required one test to detect one condition. As mass spectrometry became more widely available, the technology allowed rapid determination of a number of acylcarnitines and amino acids from a single dried blood spot. This increased the number of conditions that could be detected by newborn screening. Enzyme assays are used to screen for galactosemia and biotinidase deficiency. Immunoassays measure thyroid hormones for the diagnosis of congenital hypothyroidism and 17-hydroxyprogesterone for the diagnosis of congenital adrenal hyperplasia. Molecular techniques are used for the diagnosis of cystic fibrosis and severe combined immunodeficiency.
The goal is to report the results within a short period of time. If screens are normal, a paper report is sent to the submitting hospital and parents rarely hear about it. If an abnormality is detected, employees of the agency, usually nurses, begin to try to reach the physician, hospital, and/or nursery by telephone. They are persistent until they can arrange an evaluation of the infant by an appropriate specialist physician (depending on the disease). The specialist will attempt to confirm the diagnosis by repeating the tests by a different method or laboratory, or by performing other corroboratory or disproving tests. The confirmatory test varies depending on the positive results on the initial screen. Confirmatory testing can include analyte specific assays to confirm any elevations detected, functional studies to determine enzyme activity, and genetic testing to identify disease-causing mutations. In some cases, a positive newborn screen can also trigger testing on other family members, such as siblings who did not undergo newborn screening for the same condition or the baby's mother, as some maternal conditions can be identified through results on the baby's newborn screen. Depending on the likelihood of the diagnosis and the risk of delay, the specialist will initiate treatment and provide information to the family. Performance of the program is reviewed regularly and strenuous efforts are made to maintain a system that catches every infant with these diagnoses. Guidelines for newborn screening and follow up have been published by the American Academy of Pediatrics[16] and the American College of Medical Genetics.[17]
Newborn screening is intended as a public health program to identify infants with treatable conditions before they present clinically, or suffer irreversible damage. Phenylketonuria (PKU) was the first disorder targeted for newborn screening, being implemented in a small number of hospitals and quickly expanding across the United States and the rest of the world.[18] After the success of newborn screening for PKU (39 infants were identified and treated in the first two years of screening, with no false negative results), Guthrie and others looked for other disorders that could be identified and treated in infants, eventually developing bacterial inhibition assays to identify classic galactosemia and maple syrup urine disease.[3][18]
Newborn screening has expanded since the introduction of PKU testing in the 1960s, but can vary greatly between countries. In 2011, the United States screened for 54 conditions, Germany for 12, the United Kingdom for 2 (PKU and medium chain acyl-CoA dehydrogenase deficiency (MCADD)), while France and Hong Kong only screened for one condition (PKU and congenital hypothyroidism, respectively).[19] The conditions included in newborn screening programs around the world vary greatly, based on the legal requirements for screening programs, prevalence of certain diseases within a population, political pressure, and the availability of resources for both testing and follow-up of identified patients.
Newborn screening originated with an amino acid disorder, phenylketonuria (PKU), which can be easily treated by dietary modifications, but causes severe mental retardation if not identified and treated early. Robert Guthrie introduced the newborn screening test for PKU in the early 1960s.[15] With the knowledge that PKU could be detected before symptoms were evident, and treatment initiated, screening was quickly adopted around the world. Austria started screening for PKU in 1966[20] and England in 1968.[21]
With the advent of tandem mass spectrometry as a screening tool, several fatty acid oxidation disorders were targeted for inclusion in newborn screening programs. Medium chain acyl-CoA dehydrogenase deficiency (MCADD), which had been implicated in several cases of sudden infant death syndrome[22][23][24] was one of the first conditions targeted for inclusion. MCADD was the first condition added when the United Kingdom expanded their screening program from PKU only.[19] Population based studies in Germany, the United States and Australia put the combined incidence of fatty acid oxidation disorders at 1:9300 among Caucasians. The United States screens for all known fatty acid oxidation disorders, either as primary or secondary targets, while other countries screen for a subset of these.[25]
The introduction of screening for fatty acid oxidation disorders has been shown to have reduced morbidity and mortality associated with the conditions, particularly MCADD. An Australian study found a 74% reduction in episodes of severe metabolic decompensation or death among individuals identified by newborn screening as having MCADD versus those who presented clinically prior to screening. Studies in the Netherlands and United Kingdom found improvements in outcome at a reduced cost when infants were identified before presenting clinically.[25]
Newborn screening programs have also expanded the information base available about some rare conditions. Prior to its inclusion in newborn screening, short-chain acyl-CoA dehydrogenase deficiency (SCADD) was thought to be life threatening. Most patients identified via newborn screening as having this enzyme deficiency were asymptomatic, to the extent that SCADD was removed from screening panels in a number of regions. Without the cohort of patients identified by newborn screening, this clinical phenotype would likely not have been identified.[25]
The most commonly included disorders of the endocrine system are congenital hypothyroidism (CH) and congenital adrenal hyperplasia (CAH).[26] Testing for both disorders can be done using blood samples collected on the standard newborn screening card. Screening for CH is done by measuring thyroxin (T4), thyrotropin (TSH) or a combination of both analytes. Elevated 17-hydroxyprogesterone (17OHP) is the primary marker used when screening for CAH, most commonly done using enzyme-linked immunosorbant assays, with many programs using a second tier tandem mass spectrometry test to reduce the number of false positive results.[26] Careful analysis of screening results for CAH may also identify cases of congenital adrenal hypoplasia, which presents with extremely low levels of 17OHP.[26]
CH was added to many newborn screening programs in the 1970s, often as the second condition included after PKU. The most common cause of CH is dysgenesis of the thyroid gland After many years of newborn screening, the incidence of CH worldwide had been estimated at 1:3600 births, with no obvious increases in specific ethnic groups. Recent data from certain regions have showed an increase, with New York reporting an incidence of 1:1700. Reasons for the apparent increase in incidence have been studied, but no explanation has been found.[26]
Classic CAH, the disorder targeted by newborn screening programs, is caused by a deficiency of the enzyme steroid 21-hydroxylase, and comes in two forms - simple virilizing and a salt-wasting form. Incidence of CAH can vary greatly between populations. The highest reported incidence rates are among the Yupic Eskimos of Alaska (1:280) and on the French island of La Reunion (1:2100).[26]
Any condition that results in the production of abnormal hemoglobin is included under the broad category of hemoglobinopathies. Worldwide, it is estimated that 7% of the population may carry a hemoglobinopathy with clinical significance.[27] The most well known condition in this group is sickle cell disease.[27] Newborn screening for a large number of hemoglobinopathies is done by detecting abnormal patterns using isoelectric focusing, which can detect many different types of abnormal hemoglobins.[27] In the United States, newborn screening for sickle cell disease was recommended for all infants in 1987, however it was not implemented in all 50 states until 2006.[27]
Early identification of individuals with sickle cell disease and other hemoglobinopathies allows treatment to be initiated in a timely fashion. Penicillin has been used in children with sickle cell disease, and blood transfusions are used for patients identified with severe thalassemia.[27]
Most jurisdictions did not start screening for any of the organic acidemias before tandem mass spectrometry significantly expanded the list of disorders detectable by newborn screening. Quebec has run a voluntary second-tier screening program since 1971 using urine samples collected at three weeks of age to screen for an expanded list of organic acidemias using a thin layer chromatography method.[9] Newborn screening using tandem mass spectrometry can detect several organic acidemias, including propionic acidemia, methylmalonic acidemia and isovaleric acidemia.
Cystic fibrosis (CF) was first added to newborn screening programs in New Zealand and regions of Australia in 1981, by measuring immunoreactive trypsinogen (IRT) in dried blood spots.[28] After the CFTR gene was identified, Australia introduced a two tier testing program to reduce the number of false positives. Samples with an elevated IRT value were then analyzed with molecular methods to identify the presence of disease causing mutations before being reported back to parents and health care providers.[29] CF is included in the core panel of conditions recommended for inclusion in all 50 states, Texas was the last state to implement their screening program for CF in 2010.[30] Alberta was the first Canadian province to implement CF screening in 2006.[31] Quebec, New Brunswick, Nova Scotia, Newfoundland and Prince Edward Island do not include CF in their screening programs.[32] The United Kingdom as well as many European Union countries screen for CF as well.[32] Switzerland is one of the latest countries to add CF to their newborn screening menu, doing so in January 2011.[28]
Disorders of the distal urea cycle, such as citrullinemia, argininosuccinic aciduria and argininemia are included in newborn screening programs in many jurisdictions that using tandem mass spectrometry to identify key amino acids. Proximal urea cycle defects, such as ornithine transcarbamylase deficiency and carbamoyl phosphate synthetase deficiency are not included in newborn screening panels because they are not reliably detected using current technology, and also because severely affected infants will present with clinical symptoms before newborn screening results are available. Some regions claim to screen for HHH syndrome (hyperammonemia, hyperornithinemia, homocitrullinuria) based on the detection of elevated ornithine levels in the newborn screening dried blood spot, but other sources have shown that affected individuals do not have elevated ornithine at birth.[33]
Lysosomal storage disorders are not included in newborn screening programs with high frequency. As a group, they are heterogenous, with screening only being feasible for a small fraction of the approximately 40 identified disorders. The arguments for their inclusion in newborn screening programs center around the advantage of early treatment (when treatment is available), avoiding a diagnostic odyssey for families and providing information for family planning to couples who have an affected child.[34] The arguments against including these disorders, as a group or individually center around the difficulties with reliably identifying individuals who will be affected with a severe form of the disorder, the relatively unproven nature of the treatment methods, and the high cost / high risk associated with some treatment options.[34]
New York State started a pilot study to screen for Krabbe disease in 2006, largely due to the efforts of Jim Kelly, whose son, Hunter, was affected with the disease.[35] A pilot screening program for four lysosomal storage diseases (Gaucher disease, Pompe disease, Fabry disease and Niemann-Pick disease was undertaken using anonymised dried blood spots was completed in Austria in 2010. Their data showed an increased incidence from what was expected in the population, and also a number of late onset forms of disease, which are not typically the target for newborn screening programs.[36]
Undiagnosed hearing loss in a child can have serious effects on many developmental areas, including language, social interactions, emotions, cognitive ability, academic performance and vocational skills, any combination of which can have negative impacts on the quality of life.[13] The serious impacts of a late diagnosis, combined with the high incidence (estimated at 1 - 3 per 1000 live births, and as high as 4% for neonatal intensive care unit patients) have been the driving forces behind screening programs designed to identify infants with hearing loss as early as possible. Early identification allows these patients and their families to access needed resources to help them develop.[13]
Newborn hearing testing is done at the bedside using transiently evoked otoacoustic emissions, automated auditory brainstem responses or a combination of both techniques. Hearing screening programs have found the initial testing to cost between $10.20 and $23.37 per baby, depending on the technology used.[13] As these are screening tests only, false positive results will occur. A review of hearing screening programs found varied initial referral rates (screen positive results) from 0.6% to 16.7%. The highest overall incidence of hearing loss detection was 0.517%.[13] A significant proportion of screen positive infants were lost to follow-up, before a diagnosis could be confirmed or ruled out in all screening programs.[13]
Pulse oximetry has been recently added as a bedside screening test for critical congenital heart defects.[14]
Severe combined immunodeficiency (SCID) caused by T-cell deficiency is a disorder that was recently added to newborn screening programs in some regions of the United States. Wisconsin was the first state to add SCID to their mandatory screening panel in 2008, and it was recommended for inclusion in all states' panels in 2010. Identification of infants with SCID is done by detecting T-cell receptor excision circles (TRECs) using real-time quantitative polymerase chain reaction (RT-qPCR). TRECs are decreased in infants affected with SCID.[37]
SCID has not been added to newborn screening in a wide scale for several reasons. It requires technology that is not currently used in most newborn screening labs, as PCR is not used for any other assays included in screening programs. Follow-up and treatment of affected infants also requires skilled immunologists, which may not be available in all regions. Treatment for SCID is a stem cell transplant, which cannot be done in all centers.[37]
Duchenne muscular dystrophy (DMD) is an X-linked disorder caused by defective production of dystrophin. Many jurisdictions around the world have screened for, or attempted to screen for DMD using elevated levels of creatine kinase measured in dried blood spots. Because universal newborn screening for DMD has not been undertaken, affected individuals often have a significant delay in diagnosis. As treatment options for DMD become more and more effective, interest in adding a newborn screening test increases. At various times since 1978, DMD has been included (often as a pilot study on a small subset of the population) in newborn screening programs in Edinburgh, Germany, Canada, France, Wales, Cyprus, Belgium and the United States. In 2012, Belgium was the only country that continued to screen for DMD using creatine kinase levels.[38]
As treatments improve, newborn screening becomes a possibility for disorders that could benefit from early intervention, but none was previously available. Adrenoleukodystrophy (ALD), a peroxisomal disease that has a variable clinical presentation is one of the disorders that has become a target for those seeking to identify patients early. ALD can present in several different forms, some of which do not present until adulthood, making it a difficult choice for countries to add to screening programs. The most successful treatment option is a stem cell transplant, a procedure that carries a significant risk.[39]
Newborn screening programs participate in quality control programs as in any other laboratory, with some notable exceptions. Much of the success of newborn screening programs is dependent on the filter paper used for the collection of the samples. Initial studies using Robert Guthrie's test for PKU reported high false positive rates that were attributed to a poorly selected type of filter paper.[40] This source of variation has been eliminated in most newborn screening programs through standardization of approved sources of filter paper for use in newborn screening programs. In most regions, the newborn screening card (which contains demographic information as well as attached filter paper for blood collection) is supplied by the organization carrying out the testing, to remove variations from this source.[40]
Newborn screening tests have become a subject of political controversy in the last decade. In 2003, two California babies, Zachary Wyvill and Zachary Black, were both born with Glutaric acidemia type I. Wyvill's birth hospital only tested for the four diseases mandated by state law, while Black was born at a hospital that was participating in an expanded testing pilot program. Black's disease was treated with diet and vitamins; Wyvill's disease went undetected for over six months, and during that time the damage from the enzyme deficiency became irreversible.[41] Birth-defects lobbyists pushing for broader and more universal standards for newborn testing cite this as an example of how much of an impact testing can have.[citation needed]
Instituting MS/MS screening often requires a sizable up front expenditure. When states choose to run their own programs the initial costs for equipment, training and new staff can be significant. Moreover, MS/MS gives only the screening result and not the confirmatory result. The same has to be further done by higher technologies or procedure like GC/MS, Enzyme Assays or DNA Tests. This in effect adds more cost burden and makes physicians lose precious time. To avoid at least a portion of the up front costs, some states such as Mississippi have chosen to contract with private labs for expanded screening. Others have chosen to form Regional Partnerships sharing both costs and resources.
But for many states, screening is an integrated part of the department of health which can not or will not be easily replaced. Thus the initial expenditures can be difficult for states with tight budgets to justify. Screening fees have also increased in recent years as health care costs rise and as more states add MS/MS screening to their programs. (See Report of Summation of Fees Charged for Newborn Screening, 2001–2005) Dollars spent for these programs may reduce resources available to other potentially lifesaving programs. It has been recommended that one disorder, Short Chain Acyl-coenzyme A Dehydrogenase Deficiency, or SCAD, be eliminated from screening programs, due to a "spurious association between SCAD and symptoms.[42] However, recent studies suggest that expanded screening is cost effective (see ACMG report page 94-95 and articles published in Pediatrics[43]'.[44] Advocates are quick to point out studies such as these when trying to convince state legislatures to mandate expanded screening.
Expanded newborn screening is also opposed by among some health care providers, who are concerned that effective follow-up and treatment may not be available, that false positive screening tests may cause harm, and issues of informed consent.[45] A recent study by Genetic Alliance and partners suggests that communication between health care providers and parents may be key in minimizing the potential harm when a false positive test occurs. The results from this study also reveal that parents found newborn screening to be a beneficial and necessary tool to prevent treatable diseases.[46] To address the false positive issue, researchers from the University of Maryland, Baltimore and Genetic Alliance established a check-list to assist health care providers communicate with parents about a screen-positive result.[47]
Controversy has also erupted in some countries over collection and storage of blood or DNA samples by government agencies during the routine newborn blood screen. It was revealed that in Texas the state had collected and stored blood and DNA samples on millions of newborns without the parents' knowledge or consent. These samples were then used by the state for genetic experiments and to set up a database to catalog all of the samples/newborns. Samples obtained without parents' consent were destroyed.[48]
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