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Chapter 3. The Organization of Development
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Most people have two major linear creases across the palm of their hands (take a look). Two percent of people in the general population have a single transverse palmar crease (a so-called "simian crease"). This finding is very frequent in patients with Down syndrome. The single transverse palmar crease would be an example of
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Single transverse palmar creases would meet the definition of a "minor malformation." It is an abnormality of early (first trimester) development. It is sometimes present in normal individuals. It has no clinical significance.
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Porencephalic cysts are fluid-filled spaces in the brain that are left after the death of brain cells. A porencephalic cyst identified in an infant at 2 hours of age is the result of a
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A. malformation, and must have occurred before 11 weeks of pregnancy.
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B. malformation, but since the organ affected is the brain, must have occurred before 22 weeks of pregnancy.
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E. transfected DNA sequence.
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Since porencephaly results from normal cells that are lost due to injury, this would be a disruption.
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Dysmorphology (the area of clinical genetics concerned with diagnosis and etiology) classifies congenital anatomic malformations according to pathophysiology. This classification includes malformations, deformations, and disruptions. A fourth type exists in which there is abnormal organization of cells into tissues with its morphologic consequences. This would be defined as
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The fourth major category of congenital anomalies is dysplasia (abnormal histogenesis).
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A. are uncommon disorders that most practitioners will rarely see.
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B. in general are decreasing in frequency.
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C. are often associated with infant mortality.
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