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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.
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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.
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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 ...