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Abstract Objective: To explore the relationship between mental retardation (MR) and developmental delay (DD) of children and their chromosome karyotypes and genomic copy number variant. Methods: G band Chromosomal karyotyping and chromosomal microarray analysis (CMA) were carried out in 60 cases with MR/DD. Results: Of the 60 children with MR/DD, 11 cases (18.3%) showed autosomal chromosome abnormalities. The numbers of autosomal abnormalities were found in 5 cases, and autosomal chromosome structural abnormalities were found in 6 cases. 49 cases with normal karyotypes scanned by the CMA were found genomic copy number variants (CNVs). 1 case with CNV had microdeletion of 3q33.1 34, which was the critical region for 13q microdeletion syndrome. 1 case with CNV had microdeletion of 1p36.33 36.31, which was the critical region for 1p36 microdeletion syndrome. And 1 case with CNV had a microdeletion of 5q35.1 35.31, which was the critical region for Sotos syndrome. Moreover, 1 case with CNV had been identified with one duplications at 5q14.3, which was unknown significance CNVs. Conclusion: Chromosome abnormality and genomic CNVS are major causes of MR/DD. Chromosome karyotyping and CMA have great clinical significance in the etiological diagnosis of MR/DD.
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