Developing a national newborn screening strategy for Canada.

AuthorWilson, Kumanan

Introduction

Newborn screening is a population-based program that aims to identify disorders in neonates that could lead to mental retardation or have life-threatening consequences and for which treatments are available. Heel prick blood samples are taken from newborns in the population during the first few days of life and analysed to identify those who are at high risk of particular diseases. Diseases that are targets of newborn screening are generally rare, with the most common disease being congenital hypothyroidism with an incidence of ~1/3000 births. As well, the diseases have in common a pre-clinical phase during which diagnosis may be established, and treatment instituted, before the onset of symptoms that would otherwise bring the baby to clinical attention. The vast majority of diseases targeted by such programs internationally are of genetic etiology. Increasingly, there is interest in additional targets, especially congenital infections such as Human Immunodeficiency Virus, Cytomegalovirus and Toxoplasmosis, where early treatment may be of benefit to the infant.

Clinical benefit to the affected infant has been the historical goal of pre-symptomatic diagnosis by newborn screening, in accordance with traditional criteria for disease screening. (1) However, other reasons for newborn screening are being increasingly legitimized. These include reproductive decision-making for parents (given the autosomal recessive heritability of most of the screened diseases), avoidance of lengthy workups for the non-specific symptoms that often herald rare diseases (diagnostic odyssey), and identification of cohorts for investigational therapies that will only be effective early in the course of a disease. (2)

An increasing number of jurisdictions are expanding the number of conditions for which they screen, at least partly in response to technological advances (such as the application of tandem mass spectrometry) that have made screening for additional diseases feasible and economical on a mass population basis. However, there is considerable variability across jurisdictions in the diseases for which screening is offered, and this variability is evident in provincial programs in Canada. (3) While there are a multitude of factors that influence the decision on whether or not to screen for a condition, including provincial scientific assessment and prevalence of a condition within a province, there have been calls to nationalize the approach to the various components of newborn screening. (4) In this article we examine the rationale for a national approach and different mechanisms by which the federal government could create a national newborn screening strategy.

The state of newborn screening in other countries

The practice of newborn screening is reported to occur in at least 64 countries worldwide. (5) At the international level, the disorders targeted by newborn screening vary greatly from country to country. In part, this is due to differential prioritization of disorders based on a variety of factors which include, but are not limited to: prevalence of the target disorders in a given country, clinical practice, availability of treatment for the target disorders, and differential interpretation of both screening criteria and empirical evidence. In particular, the rarity of the screened conditions and the rapid advancement of testing technologies have meant that evidence supporting the clinical benefits of newborn screening has often not been fully available at the time the ability to incorporate additional diseases into screening panels emerged. This in turn has fueled policy debates about the appropriate criteria to justify the expansion of newborn screening programs and whether those criteria have been met for specific diseases or groups of diseases. (6)

Even within a given country, such as the United States, there has been considerable variation among states. (7) In response to the recommendations of a task force on newborn screening led by the American Academy of Pediatrics (2000), the American College of Medical Genetics (ACMG) was commissioned by the Health Services and Resources Administration (HRSA) to develop guidelines for newborn screening, with the aim of producing parity across states. The final recommendation was that 29 primary target conditions should form the core screening panel, and that an additional 25 secondary conditions should be reported when identified. (8) The 25 secondary conditions were not recommended as primary targets of the newborn screening process, in part because they were viewed as lacking evidence based treatment protocols or there was limited knowledge of their natural history, but they are often revealed in the newborn screening process for the 29 core target conditions.

The ACMG recommendations were endorsed by several groups, including the Secretary's Advisory Committee on Heritable Disorders and Genetic Diseases in Newborns and Children, the American Academy of Pediatrics, and the March of Dimes. However, some authors have been highly critical of the approach used to develop the recommendations, including the methods that were used to interpret and summarize the evidence demonstrating clinical benefits, and the consideration that was given to non-clinical benefits. (9) Indeed a systematic review of similar evidence carried out in the UK led to much more limited recommendations for the expansion of newborn screening. (10) Ultimately, the decision about whether to implement the ACMG recommendations resides with individual state health departments, although the vast majority of state programs have expanded to include universal screening for the core panel conditions. (11) A comparison of disorders screened in England, Australia and the Netherlands, compared to the ACMG recommended core panel in the United States, is listed in Table 1.

Table 1: Comparison of the ACMG recommended screening panel and conditions screened for or recommended for screening in England, Australia and the Netherlands Disorder Recommended England ACMG pane (Pollitt, (2006) (a) 2007) Congenital Hypothyroidism + + Congenital Adrenal Hyperplasia + Hemoglobinopathies (S/S, S/C, + + S/[beta]-thal) Biotinidase Deficiency + Galactosemia + Cystic Fibrosis + + Carnitine Uptake Deficiency + Long Chain 3-hydroxyacyl-CoA dehydrogenase + deficiency (LCHAD) Medium chain Acyl-CoA dehydrogenase + + deficiency (MCAD) Trifunctional protein deficiency + Very Long Chain Acyl-CoA dehydrogenase + deficiency (VLCAD) Glutaryl-CoA dehydrogenase deficiency + 3-Hydroxy-3-methylglutaryl CoA lyase + deficiency Isovaleric Acidemia + 3-Methylcrotonyl-CoA carboxylase + deficiency Methylmalonic academia (Vitamin B12 + disorders, Cbl-A, B) Beta-ketothiolase deficiency + Methylmalonyl-CoA mutase (MUT) Proprionic Acidemia + Multiple carboxylase deficiency + Argininosuccinic Aciduria + Citrullinemia + Homocystinuria + Maple Syrup Urine Disease + Phenylketonuria + + Tyrosinemia Type I + Disorder Australia Netherlands (Padilla and (Health Therrell, Council of 2007) (b) the Netherlands, 2005) Congenital Hypothyroidism + + Congenital Adrenal...

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