Risk of dominant mutation in older fathers: evidence from osteogenesis imperfecta.

The mean paternal age at birth of 80 presumed mutant cases of dominant osteogenesis imperfecta (OI) was significantly higher than that of population controls and remained so after adjusting for maternal age. There was also an increase in mean maternal age (not significant) which disappeared after adjusting for paternal age. No significant increase in maternal or paternal age was found in cases having OI either of a dominant type with an affected parent or of a type (Sillence type III) usually regarded as recessive. We conclude that, as in certain other dominant conditions, the risk of mutant OI increases with paternal age. However, the rate of increase of risk with paternal age appears to be considerably lower than, for example, in achondroplasia. The overall risk of fresh dominant mutation in older fathers may therefore be lower than has previously been suggested.