From the Department of Human Genetics, School of Public Health and Institute of Public Health Research, Tehran University of Medical Sciences, Tehran
Abstract: (4162 Views)
Cytogenetic studies were performed on 150 cases of Down's syndrome (DS)
in Iran. The standard trisomy 21 was found in 132 (88 % ) and translocation-trisomy
21 (+21) in 18 (12%) patients, i.e., t(21,21) in 1(0.63%) and mosaicism in
17(11.33%) cases.
The comparison of the frequencies for mosaicism between different
populations such as Denmark, Hungary, Egypt, Iraq, India, Australia and Iran
demonstrated a difference in geographic distribution. There was a high incidence
in the north of Europe towards Egypt and Iraq which decreased towards Iran and
further towards the eastern region in the Indian ocean and India and further
decreased towards Australia. Statistical analyses demonstrated significant
differences between the data in Iran and Copenhagen, Hungary and Australia for
mosaicism and translocation +21, and India, for translocation +21. The occurrence
of translocation +21 decreased significantly from Denmark towards Egypt in
Africa and Iraq in southwest Asia, then it increased from Iran towards Australia
in the Pacific ocean.
The comparison of cells having satellite associations (SA), significantly
indicated the involvement of two and three SAs in DS cases.
The study on the position of chromosomes in the metaphase plate, the
occurrence of chromatid breaks and endoreduplication did not present any
significance in DS cases.