OBJECTIVE: Down syndrome screening programmes lead to the prenatal diagnosis of other chromosomal abnormalities, some of which would not be detected by the secondary use of cell-free (cf)DNA testing in screen positives. This study aims to assess the number of these incidental diagnoses. METHOD: This study is a systematic review of the literature to identify large prospective screening studies that reported diagnoses other than trisomies 21 and 18. RESULTS: There were ten informative prospective studies in which a total of 1,500,999 women were screened, and there were 3689 aneuploidy cases detected in the screen positives. Trisomy 21 was estimated to comprise only 58% of detected aneuploidies, trisomies 21 and 18 comprised 72%, and the common trisomies - 21, 18 and 13 - comprised 76%. Common trisomies and sex chromosome abnormalities, now included in all commercial cfDNA tests, were estimated to comprise 87% of aneuploidies in the Down syndrome screen positives. All these proportions were higher for second trimester protocols compared with those carried out wholly or partly in the first trimester. CONCLUSION: Secondary use of cfDNA testing will lead to about one-fifth reduction in diagnoses, taking account of both undetectable aneuploidies and false-negatives. This loss might be overcome by contingent cfDNA testing.
OBJECTIVE: Down syndrome screening programmes lead to the prenatal diagnosis of other chromosomal abnormalities, some of which would not be detected by the secondary use of cell-free (cf)DNA testing in screen positives. This study aims to assess the number of these incidental diagnoses. METHOD: This study is a systematic review of the literature to identify large prospective screening studies that reported diagnoses other than trisomies 21 and 18. RESULTS: There were ten informative prospective studies in which a total of 1,500,999 women were screened, and there were 3689 aneuploidy cases detected in the screen positives. Trisomy 21 was estimated to comprise only 58% of detected aneuploidies, trisomies 21 and 18 comprised 72%, and the common trisomies - 21, 18 and 13 - comprised 76%. Common trisomies and sex chromosome abnormalities, now included in all commercial cfDNA tests, were estimated to comprise 87% of aneuploidies in the Down syndrome screen positives. All these proportions were higher for second trimester protocols compared with those carried out wholly or partly in the first trimester. CONCLUSION: Secondary use of cfDNA testing will lead to about one-fifth reduction in diagnoses, taking account of both undetectable aneuploidies and false-negatives. This loss might be overcome by contingent cfDNA testing.
Authors: Graziano Pescia; Nicolas Guex; Christian Iseli; Liam Brennan; Magne Osteras; Ioannis Xenarios; Laurent Farinelli; Bernard Conrad Journal: Genet Med Date: 2016-06-30 Impact factor: 8.822