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Paper Information

Title: 

THE MEIOTIC STAGE OF NONDISJUNCTION IN TRISOMY 21 AS INDICATED BY STR POLYMORPHIC MARKERS AMONG DOWN SYNDROMES IN IRAN

Type: PAPER
Author(s): ALE YASIN AHMAD*,REZAEI SHEYDA
 
 *MEDICAL GENETIC DEPARTMENT, NATIONAL INSTITUTE FOR GENETIC ENGINEERING AND BIOTECHNOLOGY TEHRAN, IRAN
 
Name of Seminar: NATIONAL CONGRESS OF BIOTECHNOLOGY OF IRAN
Type of Seminar:  CONGRESS
Sponsor:  IRANIAN BIOTECHNOLOGY ASSOCIATION
Date:  2005Volume 4
 
 
Abstract: 

Although, chromosome 21 trisomy, the most common cause of Down syndrome, has been studied for a long time but the mechanisms behind the etiology of this trisomy in regards to how the chromosomal abnormality appear has not yet well known. The main risk factor has been accepted till now is maternal aging factor is related exclusively to the mother; parity and father's age play no detectable role. However, the reason behind trisomy may vary between meiosis one or two timing of chromosome error. This is the first study in Iran to categorize cases of down syndromes by timing of the meiotic error of extra chromosome 21. We have studied 130 down families using conventional cytogenetic analysis and five chromosome 21 specific STR markers (D21S11, D21S1414, D21S1440, D21S1411, D21S1412) to determine timing of meiotic error to each case. Free chromosomes 21 were determined in 125 cases. The parental origin of extra chromosome 21as well as meiotic stage of chromosome 21 nondijunction were determined in 95% of cases with chromosome 21 nondisjunction whereas 5% of cases were uninformative in molecular analysis. From 114 Down syndrome cases with maternal origin, 76 (60.8%) chromosome 21 nondisjunction occurred in meiosis I and 29 (23.2%) have been detected in meiosis II. Among the 14 paternal cases, nondisjunction occurred in meiosis I in 8 (6.4%) cases and in meiosis II in 6 (4.8%) of cases. Since there was no significant difference in the distribution of maternal ages between maternal meiosis I error versus maternal meiosis II error, it is unexpected that a nondisjunction at a especial of maternal ages between maternal meiosis I error against maternal II error, related significantly to the rising incidence of Down syndrome with advancing maternal age.

 
Keyword(s): DOWN SYNDROME, STR, TRISOMY, POLYMORPHISM, NONDISJUNCTION
 
 
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