Scientists are still trying to discover why the symptoms vary so much, even among people from the same family. One theory is that each patient’s unique genetic makeup influences the severity of his or her symptoms; meaning that genes other than the NF1 gene might play a role. Scientists call these “modifier genes,” and they could be any of the thousands of genes in the human genome.

How do modifier genes work? Proteins encoded by modifier genes might work in the same biological pathways as neurofibromin, and therefore affect how well these pathways work. Variations in the DNA sequence of a modifier gene may alter its function enough to influence the severity of NF1 in an individual.

To date, scientists have not found any strong candidate NF1 modifier genes.

It’s also possible that environmental events may cause the variability among different NF patients. Also, the different types of mutations that occur in the NF1 gene may be a factor. Currently, over 500 different types of mutations have been discovered in the NF1 gene.