Neurofibromatosis/Noonan phenotype: a variable feature of type 1 neurofibromatosis

Since January 1989 we have ascertained patients with neurofibromatosis type 1 (NFl) as part of our genetic register in the North West of England. This register has now identified 453 affected cases from 235 families. The first 94 individuals were specifically examined for features of the Noonan phenotype. This was present in 12/94 sequentially identified individuals with NFl, including six individuals from three families. However, three cases occurred in a further family, where Noonan syndrome appeared to segregate separately from NFl. We have provided evidence for the chance association of Noonan syndrome and NFl and that the Noonan phenotype occurs as a feature in some NFl families. However, there is now little evidence of a separate NFl/Noonan syndrome entity or of NFl features occurring in classical Noonan syndrome.