Chapter 175

Birth defects are relatively common—about 2% of newborns will have a medically significant malformation recognized during the first day of life. However, approximately one half of all defects that are present at birth are not diagnosed until later in infancy. Defects that may not be apparent at birth include abnormalities of the central nervous system, cardiovascular system, and sensory systems (eg, hearing, vision) among others. Collectively, it appears that 4% of infants have a medically significant structural anomaly diagnosed by age 12 months.

Birth defects can be isolated abnormalities or be features of one of the thousands of known syndromes of genetic or environmental etiologies. For example, approximately 75% of children with congenital heart malformations have isolated defects, whereas additional birth defects, often comprising a syndrome, are found in the remaining 25%. The etiology of most birth defects is unknown, although it is estimated that a substantial proportion are caused by mutations in genes that control normal development. Birth defects that arise from an intrinsically abnormal developmental process are called malformations. Birth defects can also result from an alteration of the form, shape, or position of a normally formed body part by mechanical forces and are termed deformations. For example, oligohydramnios can result in abnormal mechanical constraints on the joint mobility of a fetus leading to the formation of contractures (eg, clubfoot). Birth defects may also be caused by external interference with an originally normal developmental process, known as a disruption. For example, strands of amniotic tissue that become tightly wound around a digit can result in truncation of the digit. An abnormal organization of cells into tissues, a dysplasia (eg, a congenital vascular malformation), is also considered a type of birth defect. Of note, malformations and dysplasias are primary disturbances of embryogenesis and histogenesis, respectively. Deformations and disruptions are secondary to a primary extrinsic force.

The presence of a birth defect often evokes an aura of mystery or implies a difference in personhood. Furthermore, terms such as elfin-like face and harelip implicitly reinforce these differences. Yet families who experience the birth of a newborn with a birth defect wrestle with the same questions about cause, responsibility, and outcome as any other family of a child with a serious pediatric disease. Approaching the diagnosis and management of an infant or a child with a birth defect can also be overwhelming in that thousands of different conditions are associated with birth defects, and strategies to diagnose and treat these conditions change rapidly. A logical and systematic approach to the evaluation of children with birth defects and the collection of phenotypic data are important for both diagnostic and therapeutic reasons. The recognition of a well-characterized disorder, even if the etiology is unknown, provides (1) information on the pattern of inheritance and recurrence risk, (2) the framework and options for the management of future pregnancies, and (3) information that can be used to make general predictions about potential future manifestations and outcomes and about ...

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