Mosaic Neurofibromatosis Type 1 in Children: A Single-Institution Experience

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Neurofibromatosis type 1 (NF1) is a neurocutaneous disorder caused by loss-of-function mutation in the NF1 gene. Segmental or mosaic NF1 (MNF) is an uncommon presentation of the NF1 result of postzygotic mutations that present with subtle localised clinical findings.


Our study’s objectives were to describe the clinical characteristics of children with MNF.


We conducted a cross-sectional study of children diagnosed with MNF at the Hospital for Sick Children in Toronto, Canada, from January 1992 to September 2012. Data were abstracted from health records and analysed using a standardised data collection form approved by our hospital Research Ethics Board.


We identified 60 patients with MNF; 32 of 60 (53.3%) were female. Mean ± SD age at first assessment was 10.6 ± 4.6 years. The most common initial physical manifestation in 39 of 60 (65.0%) patients was localised pigmentary changes only, followed by plexiform neurofibromas only in 10 of 60 (16.7%) and neurofibromas only in 9 of 60 (15.0%). Unilateral findings were seen in 46 of 60 (76.7%) patients. Most common associations identified included learning disabilities (7/60; 12%) and bony abnormalities (6/60; 10.0%).


MNF is an underrecognised condition with potential implications for patients. Children mostly present with pigmentary anomalies only. Most patients do not develop associated findings or complications before adulthood, but long-term follow-up will help determine outcomes and possible associations. Recognition and confirmation of the diagnosis is important to provide follow-up and genetic counselling to patients.

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