SMAD6 and congenital rubella syndrome: The SMAD6-transmitting parents had a total of 23 children unaffectedby CRS; taking account of the two affected sib pairs in the cohort, thisindicates a sib recurrence risk of 2/25 = 8%, equivalent to an estimatedpenetrance for CRS of SMAD6 variants of ~16%assuming a 50% transmission rate of the parental SMAD6 variant (unaffected offspring were not genotyped).