Objective: To define the DNA mutation causing neurofibromatosis 2 (NF2), a severe genetic disorder involving the development of multiple nervous system tumors in adulthood, in a large, well-studied NF2 pedigree previously used to chromosomally map and to isolate the disease gene.
Design: Single-strand conformational polymorphism (SSCP) and DNA sequence analysis of the NF2 gene amplified from affected and unaffected family members.
Participants: Affected, unaffected, and at-risk members of a large pedigree segregating NF2, an autosomal dominant disorder caused by inactivation of the merlin tumor suppressor encoded in chromosome band 22q12.
Results: A DNA alteration in the merlin coding sequence caused a shift on SSCP gels that was characteristic of the disease chromosome in this NF2 pedigree, being transmitted with the disorder, present only in affected members of the pedigree, absent in unaffected members of the family, and absent from 158 unrelated individuals. The alteration caused substitution of a tyrosine for an asparagine at position 220 of the merlin protein, in a region highly conserved in closely related members of the family of cytoskeletal-associated proteins. The DNA change could also be detected by restriction enzyme digestion with Rsa I.
Conclusion: Current practice dictates screening of all those "at risk" for NF2 with magnetic resonance imaging, but the frequency and duration of screening are problematic because of the variable course of the disease. The identification of a DNA alteration in the NF2 gene will permit predictive molecular testing of individuals at risk in this specific family, sparing the expense and emotional burden of protracted screening programs. This information, by providing diagnostic certainty, should also reduce psychological and financial burdens and improve medical care for affected family members. A similar approach to defining the underlying lesion and developing a predictive test is applicable in any documented NF2 family.