title: Maternal plasma DNA analysis with massively parallel sequencing by ligation for noninvasive prenatal diagnosis of trisomy 21.
abstract: BACKGROUND
  Noninvasive prenatal diagnosis of trisomy 21 (T21) has recently been shown to be achievable by massively parallel sequencing of maternal plasma on a sequencing-by-synthesis platform. The quantification of several other human chromosomes, including chromosomes 18 and 13, has been shown to be less precise, however, with quantitative biases related to the chromosomal GC content.
  
  
  METHODS
  Maternal plasma DNA from 10 euploid and 5 T21 pregnancies was sequenced with a sequencing-by-ligation approach. We calculated the genomic representations (GRs) of sequenced reads from each chromosome and their associated measurement CVs and compared the GRs of chromosome 21 (chr21) for the euploid and T21 pregnancies.
  
  
  RESULTS
  We obtained a median of 12 x 10(6) unique reads (21% of the total reads) per sample. The GRs deviated from those expected for some chromosomes but in a manner different from that previously reported for the sequencing-by-synthesis approach. Measurements of the GRs for chromosomes 18 and 13 were less precise than for chr21. z Scores of the GR of chr21 were increased in the T21 pregnancies, compared with the euploid pregnancies.
  
  
  CONCLUSIONS
  Massively parallel sequencing-by-ligation of maternal plasma DNA was effective in identifying T21 fetuses noninvasively. The quantitative biases observed among the GRs of certain chromosomes were more likely based on analytical factors than biological factors. Further research is needed to enhance the precision for measuring for the representations of chromosomes 18 and 13.
authors.affiliation: Centre for Research into Circulating Fetal Nucleic Acids, Li Ka Shing Institute of Health Sciences, Hong Kong SAR, China.
authors.forename: Rossa W K
authors.initials: RW
authors.lastname: Chiu
authors.forename: Hao
authors.initials: H
authors.lastname: Sun
authors.forename: Ranjit
authors.initials: R
authors.lastname: Akolekar
authors.forename: Christopher
authors.initials: C
authors.lastname: Clouser
authors.forename: Clarence
authors.initials: C
authors.lastname: Lee
authors.forename: Kevin
authors.initials: K
authors.lastname: McKernan
authors.forename: Daixing
authors.initials: D
authors.lastname: Zhou
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
authors.forename: Y M Dennis
authors.initials: YM
authors.lastname: Lo
mesh_terms: D002891:Chromosomes, Human, Pair 21; D004247:DNA / Q000097:blood / Q000235:genetics*; D004314:Down Syndrome / Q000175:diagnosis* / Q000235:genetics; D005260:Female; D005820:Genetic Testing / Q000379:methods; D006801:Humans; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D017422:Sequence Analysis, DNA / Q000379:methods
chemical_list: D004247:DNA