Identification of an i(21q) by Using Dinucleotide Repeat Polymorphisms / 대한임상병리학회지

ABSTRACT

BACKGROUND: Recent DNA polymorphism analysis using numerous DNA markers has been used to determine the parental origin of the extra chromosome 21 in Down syndrome. In this study we used seven dinucleotide repeat polymorphisms on chromosome 21 to characterize a case of rea(21q21q) and to know whether it is consistent with an isochromosome or a true Robertsonian translocation. METHODS: Cytogenetic investigation was done by conventional G banding DNA was extracted from whole blood of a proband and her parents and was amplified by PCR using seven sets of (GT)n repeat dinucleotide markers located on the long arm of chromosome 21 After electrophoresis of the PCR product in polyacrylamide gel and silver staining the parental origin and number of DNA copy were determined by visual comparison of the band intensities within and between individuals. RESULTS: Conventional cytogenetics showed that the proband had a 46.XX.re(21q21q) chromosome pattern. Parental chromosome studies were normal, therefore, the rearrangement was a de novo event. All seven DNA markers showed one or two alleles, demonstrating rea(21q21q) to be an isochromosome. For D21S215 and D21S156 markers both parents were heterozygous and the proband inherited one copy of paternal allele and two copies of maternal allele which both parents did not share. This finding was consistent with a maternally derided isochromosome. CONCLUSION: Use of dinucleotide repeat DNA polymorphisms after PCR amplification will be very useful to detect the parental origin of additional chromosome 21 or rearrangement of chromosome 21 in Down syndrome. Besides employing siltier staining of a PCR product we will be able to avoid using of radioisotopes and apply to clinical laboratory diagnosis.