Since the discovery of circulating cell-free DNA (cfDNA) in the plasma of pregnant women in the late 1990s,1,2  its potential for prenatal diagnosis has been the focus of intensive technological innovation. Screening for chromosomal abnormalities is now introduced in several countries, including the United Kingdom. However, the so-called combined test (which utilizes ultrasound scanning to measure fetal nuchal translucency, maternal age, and blood tests to measure pregnancy-associated plasma protein A and free β-human chorionic gonadotrophin) remains the first-stage test. Women at high risk of carrying an affected baby are offered noninvasive prenatal testing (NIPT), and if this returns a positive result, they are given the option of confirmatory invasive testing by amniocentesis.

Technologies detecting dominant de novo mutations or dominant mutations of paternal origin from cfDNA have been previously described. For recessive disorders...

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