The hunt for the neurofibromatosis gene

The neurofibromatosis type 1 (NF1) gene has been localized to the pericentromeric region of the long arm of chromosome 17. A chronology of events leading to the cloning of the NF1 gene is offered as a summary of modern gene hunting techniques. The gene was identified by its location rather than its function using positional cloning. Linkage analysis, based on DNA polymorphisms, is already available for prenatal and presymptomatic testing. This technique works only in cases when affected family members are available and is useless in spontaneous cases. The complete NF1 gene is huge, has a large number of exons, and is approximately 240,000 base pairs long. Its large size is consistent with the very high spontaneous mutation rate. The NF1 gene is evolutionarily conserved and expressed ubiquitously, not just in neural crest derivatives. Functional and structural homology with GAP (GTP [guanosine triphosphate]ase-activating protein) has been described. The GAP controls (or is controlled by) the ras oncogene. Aberration of ras function, which plays a fundamental role in growth, development, and differentiation, may play a role in the NF1 phenotype. Direct DNA diagnosis of mutations in the NF1 gene in clinical practice is premature. Current data suggest that the NF1 gene product may act as a tumor suppressor.