It is reported that significantly reduced expression levels of neurofibromin isoform I mRNA are correlated with a severe phenotype of NF1 features, including learning disabilities/cognitive deficit, optic gliomas, and/or neoplasm/cerebrovascular disease, by analyzing the levels of two neurofibromin isoforms in circulating leukocytes of a cohort study (31). This evidence concerns the gene NF1 and Cognitive impairment.