title: High resolution size analysis of fetal DNA in the urine of pregnant women by paired-end massively parallel sequencing.
abstract: BACKGROUND
  Fetal DNA in maternal urine, if present, would be a valuable source of fetal genetic material for noninvasive prenatal diagnosis. However, the existence of fetal DNA in maternal urine has remained controversial. The issue is due to the lack of appropriate technology to robustly detect the potentially highly degraded fetal DNA in maternal urine.
  
  
  METHODS
  We have used massively parallel paired-end sequencing to investigate cell-free DNA molecules in maternal urine. Catheterized urine samples were collected from seven pregnant women during the third trimester of pregnancies. We detected fetal DNA by identifying sequenced reads that contained fetal-specific alleles of the single nucleotide polymorphisms. The sizes of individual urinary DNA fragments were deduced from the alignment positions of the paired reads. We measured the fractional fetal DNA concentration as well as the size distributions of fetal and maternal DNA in maternal urine.
  
  
  RESULTS
  Cell-free fetal DNA was detected in five of the seven maternal urine samples, with the fractional fetal DNA concentrations ranged from 1.92% to 4.73%. Fetal DNA became undetectable in maternal urine after delivery. The total urinary cell-free DNA molecules were less intact when compared with plasma DNA. Urinary fetal DNA fragments were very short, and the most dominant fetal sequences were between 29 bp and 45 bp in length.
  
  
  CONCLUSIONS
  With the use of massively parallel sequencing, we have confirmed the existence of transrenal fetal DNA in maternal urine, and have shown that urinary fetal DNA was heavily degraded.
authors.affiliation: Centre for Research into Circulating Fetal Nucleic Acids, Department of Chemical Pathology, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China. nancytsui@cuhk.edu.hk
authors.forename: Nancy B Y
authors.initials: NB
authors.lastname: Tsui
authors.forename: Peiyong
authors.initials: P
authors.lastname: Jiang
authors.forename: Katherine C K
authors.initials: KC
authors.lastname: Chow
authors.forename: Xiaoxi
authors.initials: X
authors.lastname: Su
authors.forename: Tak Y
authors.initials: TY
authors.lastname: Leung
authors.forename: Hao
authors.initials: H
authors.lastname: Sun
authors.forename: K C Allen
authors.initials: KC
authors.lastname: Chan
authors.forename: Rossa W K
authors.initials: RW
authors.lastname: Chiu
authors.forename: Y M Dennis
authors.initials: YM
authors.lastname: Lo
mesh_terms: D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000652:urine*; D005260:Female; D005333:Fetus / Q000378:metabolism*; D059014:High-Throughput Nucleotide Sequencing / Q000379:methods*; D006801:Humans; D020738:Leptin / Q000235:genetics; D008297:Male; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011247:Pregnancy; D017422:Sequence Analysis, DNA / Q000379:methods*
chemical_list: D020738:Leptin; D004247:DNA