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Molecular studies of trisomy 18
J M Fisher1, J F Harvey, R H Lindenbaum
1Wessex Regional Genetics Laboratory, Salisbury District Hospital, United Kingdom.
American Journal of Human Genetics
|June 1, 1993
Summary
The additional chromosome in most trisomy 18 cases is maternal. Paternal origin and postzygotic errors are rare causes of this genetic condition.
Area of Science:
- Genetics
- Reproductive Biology
- Developmental Biology
Background:
- Trisomy 18 (Edwards syndrome) is a common chromosomal abnormality.
- Understanding the parental origin of the extra chromosome is crucial for genetic counseling and recurrence risk assessment.
Purpose of the Study:
- To determine the parental origin of the extra chromosome in 50 cases of trisomy 18.
- To investigate the occurrence of postzygotic errors in trisomy 18.
- To compare nondisjunction patterns in trisomy 18 with those in trisomy 21 and X.
Main Methods:
- Microsatellite analysis was used to trace the parental origin of chromosome 18.
- Analysis of genetic markers to identify potential postzygotic errors.
Main Results:
- In 48 out of 50 cases, the additional chromosome 18 was of maternal origin.
- In 2 cases, the additional chromosome 18 was of paternal origin.
- Seven cases, including the two with paternal origin, were identified as resulting from postzygotic errors.
Conclusions:
- The majority of trisomy 18 cases arise from maternal nondisjunction.
- Paternal nondisjunction and postzygotic errors are infrequent causes of trisomy 18.
- Unlike trisomy 21 and X, trisomy 18 shows no evidence of nullisomic gamete nondisjunction.