Figure 5
SCD NIPT on negative control cfDNA resulted in no false-positives. Optimized HBB probes were validated for use on cfDNA by performing the NIPT assay on 10 mL of venous blood from non-pregnant compound heterozygotes (HbAS or HbSC). The mean HbS AF was 0.498 with a coefficient of variation of 2.2% (n = 30). The mean number of HBB molecules assayed in each blood tube was 3500. Our results agree with the expected HbS AF = 1/2 and CV = 1.7%; the histogram of measured HbS AF corresponds very well with the theoretical binomial distribution in blue (AF = 1/2, n = 3500). Assuming that positive cases have a 10% fetal fraction (red curve), none of the negative controls would have been called as positive for fetal SCD. (B) Assayed genomic equivalents of HBB exon 1 in cfDNA. The concentration of 13 cfDNA samples was quantified by Qubit to determine the mass of cfDNA used in the HBB assay. On average, 1 ng of cfDNA resulted in the capture of 129 haploid genomic equivalents of HBB.
