Proof-of-principle studies of this approach have demonstrated clinical utility for fetuses of families at risk for autosomal recessive conditions including congenital adrenal hyperplasia (CYP21A2), β-thalassaemia (HBB), and Ellis-van Creveld syndrome (EVC, EVC2)[106], as well as the X-linked conditions haemophilia (F8, F9), Hunter syndrome (IDS, IDS2)[106], and Duchenne or Becker muscular dystrophy (DMD)[108]. This evidence concerns the gene CYP21A2 and congenital adrenal hyperplasia.