Deciphering the genetic modifiers of clinical variability in neurofibromatosis 1: a new functional model of NF1 – MODIFUN-NF

Neurofibromatosis type 1 (NF1) is caused by dominant loss-of-function variants of the NF1 gene encoding neurofibromin, a negative regulator of RAS proteins. NF1 is characterized by a wide range of clinical expression symptoms, including skin hyperpigmentation, as well as benign peripheral nerve sheath tumors called neurofibroma (resulting from Schwann cell proliferation). Pigmentation anomalies and neurofibromas are a major concern in patients with NF1. One barrier to progress in addressing NF1 lesions is the high variability in clinical expression. Clinical outcome cannot be predicted by the type of NF1 pathogenic variant. Recently, we identified candidate modifier genes for pigmentation anomalies and neurofibromas, by using a genome-wide association study.
We aim to perform in vitro functional validations of candidate modifier genes for NF1-associated (1) pigmentary lesions and (2) neurofibromas:
1. In an in vitro system of differentiation of hiPSCs from NF1 patients into melanocytes, we aim to individually target the candidate modifier genes of NF1-associated pigmentary lesions. We will then use a variety of approaches to validate their functional effects.
2. In an in vitro CRISPR/Cas9 dropout competitive test with immortalized human Schwann cells, we aim to evaluate the functional impact of the candidate genes. This screen will narrow down the list of candidate modifier genes of neurofibroma development to be tested in an in vitro NF1-loss neural crest cell lineage (hiPSCs, neural crest cells, and Schwann cells). We will investigate how the targeting of the modifier genes with CRISPR/Cas9, at different stages of differentiation, influences neural crest cell identity and Schwann cell differentiation.
As modifier genes are functionally confirmed, we can look forward to risk stratification and mitigation for NF1 lesions. These results may shed new light on NF1 pathogenesis and will contribute to the development of personalized care in a life-threatening condition