Patent ID: 7655399

Claim:
A method for prenatal diagnosis of chromosomal abnormality in a predetermined DNA region comprising the steps of: a) obtaining a plasma sample from a pregnant female; b) enriching fetal DNA regions in the plasma sample by digesting DNA from said plasma sample with a methyl-sensitive enzyme that selectively and substantially completely digests the maternal DNA to obtain a sample enriched for fetal DNA regions; and c) determining the paternal and maternal allele frequency in the sample enriched for fetal DNA using polymorphic markers adjacent to or within the fetal DNA regions in the sample enriched for the fetal DNA regions of step (b), wherein a difference in allele frequency from other than 50% of paternal and 50% of maternal allele as compared to a normal control, which does not comprise a chromosomal abnormality is indicative of a chromosomal abnormality.