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Learning Objectives

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  1. Identify the clinical testing of situations that indicate the need for prenatal testing of mother and/or infant, and the clinical consequences of premature birth.

  2. Understand the rationale for selection of laboratory tests in neonatal screening programs.

  3. Learn the assessment for diagnosis of Down syndrome and the clinical situations in which it is most often performed.

  4. Learn the underlying defects that produce hemolytic disease of the newborn and cystic fibrosis and the laboratory test abnormalities associated with these disorders.

  5. Learn the names of the diseases and the associated biochemical defects for the more commonly encountered or better characterized inborn errors of metabolism in the following categories:

    • Amino acidurias not involving urea cycle enzymes

    • Amino acidurias involving urea cycle enzymes

    • Lysosomal storage diseases with impaired degradation of sphingolipids

    • Lysosomal storage diseases with impaired degradation of mucopolysaccharides

    • Lysosomal storage diseases with impaired degradation of glycogen

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Introduction

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It is difficult to precisely identify the diseases of infancy and childhood because many disorders that begin in childhood become clinically evident in adulthood if a long period of time is required to generate a pathologic lesion. The topics chosen for inclusion in this chapter are disorders presenting almost exclusively in childhood. However, they obviously represent only a small fraction of “childhood disorders.” Many disorders in other sections of this book, such as hemophilia and numerous infections, occur or are diagnosed primarily in childhood. The chapter begins with an overview of prenatal and neonatal laboratory testing.

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Prenatal and Neonatal Laboratory Testing

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Prenatal Testing and Screening

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The disorders that can be diagnosed before birth number in the thousands. In families in which there is a history of a particular disorder, it is not uncommon to test prenatally for that particular disorder, often with DNA-based diagnostic tests. However, for the vast majority of families without a history of a specific illness, prenatal screening may also be undertaken. A screen differs from a test in that it does not provide a definitive diagnosis but rather an assessment of the risk of a diagnosis. For most of these families, screening is preferred as an initial step because it is less invasive; for example, there are several maternal serum screening assays (see below) for fetal Down syndrome (also known as trisomy 21), but testing for fetal Down syndrome requires an invasive procedure such as chorionic villus sampling or collection of amniotic fluid. The decision to screen is a personal one for families and includes considerations such as parental age and desire to avoid having a diseased child.

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Neonatal screening was introduced as a means to detect disorders in which immediate treatment can result in the prevention of catastrophic consequences.

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Neonatal Screening

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Neonatal screening was originally developed to detect diseases such as phenylketonuria (PKU) and congenital hypothyroidism, for which early detection and intervention could prevent catastrophic ...

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