Chapter 3. The Organization of Development
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
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.
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
A. malformation, and must have occurred before 11 weeks of pregnancy.
B. malformation, but since the organ affected is the brain, must have occurred before 22 weeks of pregnancy.
E. transfected DNA sequence.
Since porencephaly results from normal cells that are lost due to injury, this would be a disruption.
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
The fourth major category of congenital anomalies is dysplasia (abnormal histogenesis).
A. are uncommon disorders that most practitioners will rarely see.
B. in general are decreasing in frequency.
C. are often associated with infant mortality.