Objects: The cytogenetic study was designed to investigate the association between mental retardation and chromosomal disorders including fragile X. Methods: Subjects were consists of 30 children(17 males, 13 females) and their age varied 24 to 228 months. The severities of mental retardation were mild in 26 patients, moderate in 1 patient and severe in 3 patients. The peripheral blood was cultured in medium 199 with methotrexate and without methotrexate for 70 hours. Thirty metaphase cells, in each were karyotype in all samples. Results • Chromosomal abnormalities were found in 10 patients, but fragile X was negative in according to Jacob’ s positive criteria( = 4%) in all patients, although 1 fragile X (3.3%) was found in 1 patient Chromosomal abnormalities were present on group A, B, C, D, E and X. There was no regional specificity of chromosomal abnormalities. Types of chromosomal disorders were only fragile and/or gap but no numerical abnormality was present in all cases(46 X X or 46XY). Number of cells which revealed fragile sites were 29 cells (3.2%) out of 900 cells. -Number of cells which revealed gaps were 35 cells(3.9%) out of 900 cells. Conclusions : These results suggest that fragile X syndrome was not found in mentally retarded patients. If further studies are performed in larger sample size, selected objects and special blood culture methods, the results may change.
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