A novel non‐invasive prenatal sickle cell disease test for all at‐risk pregnancies

Abstract

Sickle cell disease (SCD) is the most common genetic haematological disorder. The availability of non‐invasive prenatal diagnosis (NIPD) is predicted to increase uptake of prenatal diagnosis for SCD, as it has no perceived procedure‐related miscarriage risk. We report the development of a targeted massively parallel sequencing (MPS) assay for the NIPD of fetal SCD using fetal cell‐free (cf)DNA from maternal plasma, with no requirement for paternal or proband samples. In all, 64 plasma samples from pregnant women were analysed: 42 from SCD carriers, 15 from women with homozygous (Hb SS) SCD and seven from women with compound heterozygous (Hb SC) SCD. Our assay incorporated a relative mutation dosage assay for maternal carriers and a wild type allele detection assay for affected women (Hb SS/Hb SC). Selective analysis of only smaller cfDNA fragments and modifications to DNA fragment hybridisation capture improved diagnostic accuracy. Clinical sensitivity was 100% and clinical specificity was 100%. One sample with a fetal fraction of <4% was correctly called as ‘unaffected’, but with a discordant genotype (Hb AA rather than Hb AS). Six samples gave inconclusive results, of which two had a fetal fraction of <4%. This study demonstrates that NIPD for SCD is approaching clinical utility.