Abstract: 　Objective　To explore the potential structural abnormalities in copy number variation. Method　Four mentally retardated children with copy number variant complicated with multiple malformations were examined by combination of conventional karyotype analysis and FISH molecular biology techniques for identification of their chromosome structural abnormalities, and then prenatal diagnosis and follow-up were carried out in two families. Results　Four children were found to have copy number variations by chromosome microarray detection, which were 16pter deletion/19qter duplication, 18pter deletion/18qter duplication, 13qter deletion and 3p13-14 deletion respectively. Potential structural abnormalities were identified by the combination of karyotype analysis and FISH detection: one case of chromosome end imbalance translocation der (16) t (16p; 19q), one case of inverted repetitive deletion invdup18p/ del 18q, one case involving a telo-satellite translocation (13qs), and one case of a parent balanced insertion recombination leading to 3p interstitial deletion or duplication. Among them, 2 cases were caused by familial balanced reorganization, one case was unknown for the cause but at risk of recurrence, and one case had a new change. Prenatal diagnosis was performed in 2 families in the second trimester, and the follow-up results were consistent with the prenatal diagnosis. Conclusion　Chromosome microarray can detect potential chromosomal structural abnormalities in patients with simple copy number variation. Application of multiple techniques combined can identify potential structural abnormalities and provide accurate risk assessment for recurrence, so as to achieve prenatal diagnosis of diseases. Key

Key words: 　copy number variation;　chromosomal karyotype;　chromosomal microarray;　fluorescence in situ hybridization