Journal of the Korean Pediatric Society 1997;40(7):917-924.
Published online July 15, 1997.
Extrachromosome 21 in Korean with Down Syndrome Using DNA Haplotyping
Jin-Sung Lee, Won Kyu Choi
Department of Pediatrics, Yonsei University College of Medicine, Seoul, Korea
Down 증후군 환자에서 DNA Haplotyping을 이용한 분자유전학적 진단 및 발병 기전의 분석
이진성, 최원규
연세대학교 의과대학 소아과학교실
Abstract
Purpose
: Down syndrome, the most common single cause of mental retardation, is usually due to meiotic nondisjunction leading to trisomy 21. In order to understand the mechanisms of meiotic nondisjunction including parental origin of an extrachromosome and the meiotic stage of nondisjunction, we have studied DNA polymorphisms at loci on the long arm of chromosome 21 in 36 families with free trisomy 21.
Methods
: A total of 36 patients with Down syndrome who was cytogenetically diagnosed, and their parents were included in the study. The D21S11 locus was analysed using PCR follwed by denaturing polyacrylamide gel electrophoresis.
Results
: The observed heterozygosity of D21S11 locus is 79.4% in the 104 unrelated Korean. Seven alleles with different sizes were observed. The parental origin of the extrachromosome 21 could be determined in 27 of 36 cases. The maternal origin was in 24(88.9%) cases and paternal origin was in 3 cases(11.1%). Among informative cases, the meiotic error occurred at the first maternal meiosis in 9(57.3%) cases and second meiosis in 7(42.7%) of 16 cases. All paternal meiotic error occurred in the second meiosis.
Conclusion
: DNA haplotyping of the short tandem repeats markers can be very useful technique for molecular diagonosis and for determination of the parental origin of an extrachromosome 21 in Down syndrome. Nondisjunction of the maternal gamate is the main cause of trisomy 21, However, further studies with other polymorphic markers that locate at the centromere of chromosome 21 are needed in order to definitely determine the meiotic stage of nondisjunction in trisomy 21.
Key Words: Down syndrome, Nondisjunction, DNA polymorphism, Chromosome


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