Genome-wide normalized score: A novel algorithm to detect fetal trisomy 21 during non-invasive prenatal testing
Journal
Ultrasound in Obstetrics and Gynecology
Journal Volume
25
Journal Issue
30
Pages
25-30
Date Issued
2014
Author(s)
Abstract
OBJECTIVES: Non-invasive prenatal testing for fetal trisomy 21 (T21) by massively parallel shotgun sequencing (MPSS) is available for clinical use but its efficacy is limited by several factors, e.g. the proportion of cell-free fetal DNA in maternal plasma and sequencing depth. Existing algorithms discard DNA reads from the chromosomes for which testing is not being performed (i.e. those other than chromosome 21) and are thus more susceptible to diluted fetal DNA and limited sequencing depth. We aimed to describe and evaluate a novel algorithm for aneuploidy detection (genome-wide normalized score (GWNS)), which normalizes read counts by the proportions of DNA fragments from chromosome 21 in normal controls. METHODS: We assessed the GWNS approach by comparison with two existing algorithms, i.e. Z-score and normalized chromosome value (NCV), using theoretical approximations and computer simulations in a set of 86 cases (64 euploid and 22 T21 cases). We then validated GWNS by studying an expanded set of clinical samples (n = 208). Finally, dilution experiments were undertaken to compare performance of the three algorithms (Z-score, NCV, GWNS) when fetal DNA concentration was low. RESULTS: At fixed levels of significance and power, GWNS required a smaller fetal DNA proportion and fewer total MPSS reads compared to Z-score or NCV. In dilution experiments, GWNS also outperformed the other two methods by reaching the correct diagnosis with the lowest range of fetal DNA concentrations (GWNS, 3.83-4.75%; Z-score, 4.75-5.22%; NCV, 6.47-8.58%). CONCLUSION: Our results demonstrate that GWNS is comparable to Z-score and NCV methods regarding the performance of detecting fetal T21. Dilution experiments suggest that GWNS may perform better than the other methods when fetal fraction is low.
Type
journal article