Nosological considerations of the neurofibromatoses.

We are on the threshold of evaluating the NF1 and NF2 loci with respect to variant forms of the neurofibromatoses. Genetic mapping of NF1, gene cloning and characterization of its encoded product, neurofibromin, provides a framework for the evaluation of the variant forms of NF. This may also apply to NF2 variant forms in the near future. The mapping approach in evaluating variant forms of NF should begin with the rigorous clinical assessment of familial cases whereby the establishment of genetic linkage in families with overlap syndromes might determine if either NF1, NF2, or a separate locus is involved in the phenotype. Conditions mapping to the NF1 locus could then be screened for mutations in hopes of identifying the etiologies of the variant forms of NF. Mutation identification should provide a molecular-based classification scheme for the variant forms of NF, now tentatively divided into alternative and related forms. It is expected that the nosology of the neurofibromatoses will most certainly change as more is learned of the NF1 and NF2 loci.