Diagnosis Accuracy of Noninvasive Screening by PCR Digital for Down Syndrom
Condition: Trisomy 21
MeSH terms: Down Syndrome; Trisomy
Study type: Observational

Summary: 
      The main objective of this study is to estimate the intrinsic diagnostic qualities of the
      digital dPCR in the screening of T21 from a multicentrique sample of patients with
      pregnancies at high risk of T21 (risk > 1/250).

      The profit expected from this technique is to propose to the encircled women a screening more
      successful than that of the screening combined(organized) of the 1st quarter, simple of
      realization and in a moderate cost. We thus propose here an original alternative(alternate)
      method to the exclusive, expensive and binding techniques of top-debit(-flow). The recent
      technical improvements and his(her,its) advantages medical - economic allow to envisage a
      reliable, strong and long-lasting use of the dPCR in clinical routine in the DPNI of T21 in
      most of the laboratories. This pilot project could serve for the later development of a study
      of clinical validation multicentrique of large scale(big turntable ladder).
    

Detailed description: 
      Context

      Currently, non-invasive screening test for trisomy 21 (Down syndrome) is proposed to every
      pregnant woman. This first trimester combined test consists of ultrasound nuchal translucency
      measurement, associated with different maternal serum biochemical assay and maternal age.

      Since the discovery of the presence of cell-free fetal DNA in maternal plasma, the
      noninvasive prenatal testing (NIPT), using mainly a massive parallel sequencing (MPS)
      approach, has been introduced. The chromosomal origin of each sequenced plasma DNA molecule
      and the over- or under-representation of any chromosome can be identified by MPS in maternal
      plasma. The specificity and sensibility of such high-throughput techniques are excellent,
      close to 100 %. However, MPS remains time-consuming, very expensive (> 1000 euros per
      patient) and can't be used in clinical routine in most genetics laboratories worldwide.

      Digital PCR represents an interesting alternative to the MPS due to its targeted approach,
      cost (>10x less than MPS), speed and relative simplicity allowing a clinical routine
      practice. However, its clinical an analytical relevance remains insufficiently demonstrated
      in literature data . Therefore, our main objective is to evaluate the diagnosis accuracy of
      noninvasive screening by PCR digital for Down syndrome.

      Expected results This study will assess the sensitivity, specificity and likelihood ratio
      with a satisfactory accuracy. The no call rate will be also evaluated and considered as a
      positive test.

      The optimal number of replicates (leading to a false positive rate <5%) will be determined
      using a ROC curve. Our hypothesis is that the sensitivity of the screening test will be upper
      to 95% with a false positive rate <5%.

      If results are conclusive, this pilot project will be a strong argument in favor of the
      development of a further large scale study. It may challenge current screening strategy and
      allow to propose an inexpensive, fast, and accessible NIPT of trisomy 21 to a large number of
      laboratories in our territory.

      Experimental design We will evaluate this approach on a pregnant women cohort with high risk
      for T21 (>1/250), prospectively recruited from three regional hospitals with a cytogenetics
      laboratory. We propose to preform single-blind retrospective analyses of cell free DNA of 100
      pregnancies (including 70 euploid and 30 T21fetuses). Results obtained with the dPCR approach
      will be compared with the fetal karyotype beforehand performed. Digital PCR analyses will be
      performed at the Grenoble University Hospital, our team having a significant experience in
      digital PCR technology. Digital PCR reactions will be done on a QuantStudio™ 3D
      (LifeTechnologies) with the commercial high density chips etched with 20,000
      consistently-sized nanoscale reaction wells. To improve the analytical sensitivity, 10
      replicates will be performed for each patient.
    

Intervention name(s): Diagnostic
Intervention type(s): Genetic
Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Sample multicentrique of patients with pregnancies at high risk of T21 (risk > 1/250)
      
Biospecimen description: 
      It is DNA samples of 100 pregnancies including 70 euploïdes foeti and 30 trisomies 21, the
      diagnosis of which will beforehand have been made by the foetal karyotype.
    
Keywords: Non invasive prenatal testing; Down Syndrome; Digital PCR