Although few previous cases about isochromosome 18p have been reported in some clinics and research fields based on various technology platform,there has not a Satisfactory explanation of the correlations between isochromosome 18p and the special phenotypes.This present study was designed to use the CMA (chromosomal microarray analysis) platform for genetic screening in the boy with tetrasomy 18p syndrome,FISH(fluorescence in situ hybridization)and RT-qPCR (real time qPCR) were further analyzed to evaluate accuracy of the CMA result.we detected a18.4Mb pure duplication at 18p11.32q11.1 and located its accurate breakpoint at chro18∶18,546,933.The present results indicates that a high-resolutional and sensitive chromosomal microarray analysis platform is able to detect minor abnormalities,such as chromosome microduplication and/or microdeletion in human.Gentic screening of the copy number variants(CNVs) by DNA microarray anlysis is an advance techonology used for Patients suspicious of chromosomal abnormalities.