Uniparental foetal disomy: invasive diagnosis
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The principle of the SNP array is the hybridization of engineered tested DNA (amplification, fragmentation, precipitation and resuspension) to immobilised probes on the chip, specific labelling with a fluorescent dye and subsequent scanning of the fluorescent signal on the chip with a scanner (iScan). The scanner reads information for each SNP examined – genotype and signal strength. Using special evaluation software, changes in CNV (Copy Number Variation) and neutral changes in AOH (Absence of Heterozygozity) are detected. The software virtually compares the patient’s data with the control group; control samples are not used for SNP array. Illumina chips with >700,000 markers are used for CNV and AOH analysis. The result is a report with cytogenetic notation of findings according to the current ISCN nomenclature. The report includes a comment on the result, a statement on the degree of pathogenicity of the findings (also taking into account clinical data on the family, patient/foetus) and recommendations for possible follow-up examinations. The report also includes the distinction of the method and its limitations.