Congenital Heart Disease (Atrioventricular Septal Defect) in the Mouse with Trisomy 16

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Seo, Jeong-Wook; Choi, Jung-Yun; Han, Young-Mee; Kim, Jung-Sun
Issue Date
Seoul National University College of Medicine
Seoul J Med 1995;36(2):69-78
Atrioventricular canal malformationEndocardial cushion defectDown's syndromeMyocardial development
Failure of fusion between the superior and inferior cushions has
usually been assumed to be the main morphogenetic event in producing hearts
with deficient atrioventricular septation (atrioventricular septal, or endocardial cushion
defects). Morphological studies on human autopsy specimens, however, showed
that another consistent finding is the marked disproportion between the dimensions
of the inlet and outlet of the left ventricle, which, until now, has no known
developmental basis.
We have studied the early formation of the hearts with atrioventricular septal
defects, using a mouse model with trisomy 16. Animals were studied between the
10th and 19th days of gestation by stereomicroscopic examination, scanning electronmlcroscopy
and the in-vitro incorporation of thymidine.
The first detectable morphological abnormality of the heart in the trisomic
mouse was observed on the 11th day, being a persistence of an infolding at the
inferior atrioventricular junction. This infolding was present in both trisomic and
eusomic animals on the 10th day. This morphology could be explained by a differential
growth of the myocardium at the inferior atrioventricular junction, which
was found to be a distinct zone with low incorporation of thymidine. On the 11th
day, the inferior atrioventricular cushion was bigger in the trisomic hearts. The
abnormalities of the cushions observed on the 12th day or later were deemed to
be consequences of these primary defects.
Sectioning of the heart from the left lateral aspect convincingly showed morphological
changes of the superior and inferior cushion or bridging leaflets in this
animal model. Abnormal endocardial cushions and abnormality in the proliferation
index of the myocardium at the inferior atrioventricular junction play more significant
roles in the formation of the hearts with deficient atrioventricular septation,
than the abnormalities found in the atrioventricular cushions.
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College of Medicine/School of Medicine (의과대학/대학원)Dept. of Medicine (의학과)The Seoul Journal of MedicineThe Seoul Journal of Medicine Vol. 36 No.2 (1995)
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