Comprehensive RNA Analysis of the NF1 Gene in Classically Affected NF1 Affected Individuals Meeting NIH Criteria has High Sensitivity and Mutation Negative Testing is Reassuring in Isolated Cases With Pigmentary Features Only

Background: The detection rate for identifying the underlying mutation in neurocutaneous syndromes is affected by the sensitivity of the mutation test and the heterogeneity of the disease based on the diagnostic criteria. Neurofibromatosis type (NF1) has been defined for 29 years by the National Institutes for Health (NIH) criteria which include >= 6 Cafe au fait macules (CAL) as a defining criterion. The discovery of SPREDI as a cause of Legius syndrome which is manifested by CAL, freckling and learning difficulties has introduced substantial heterogeneity to the NIH criteria. Methods: We have defined the sensitivity of comprehensive RNA analysis on blood of presumed NF1 patients meeting NIH criteria with at least one rampigmentary criterion and determined the proportion of children with >= 6 CAL and no family history that has an NF1 or SPRED1 genetic variant. RNA analysis was carried out from 04/2009-12/2015 on 361 NF1 patients. Findings: A presumed causative NF1 mutation was found in 166/171 (97.08`,.6-95% Cl 94.56-99.6%) of familial cases and 182/190 (95.8%-95% CI 92.93-98.65%) sporadic de novo cases. Two of thirteen (15%) mutation negative individuals had dysembryoplastic neuroepithelial tumour (DNET) compared to 2/348 (0.6%) with an Nil variant (p = 0.007). No SPRED1 variants were found in the thirteen individuals with no NF1 variant. Of seventy-one individuals with >= 6 CAL and no non-pigmentary criterion aged 0-20 years, 47 (66.2%) had an NH variant six (85%) a SPREDI variant and 18 (253%) no disease causing variant. Using the 95.8% detection rate the likelihood of a child with 6 CAL having constitutional NFl drops from 2/3 to 1/9 after negative RNA analysis. Interpretation: RNA analysis in individuals with presumed NFl has high sensitivity and includes a small subset with DNET without an Nil variant. Furthermore negative analysis for NF1/.SPRED1 provides strong reassurance to children with 6 CAL that they are unlikely to have NFL (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://cTeativecommons.org/licenses,iby-nc-nc1/4.0/).