DNA diagnosis of neurofibromatosis 2. Altered coding sequence of the merlin tumor suppressor in an extended pedigree
M. MacCollin, T. Mohney, J. Trofatter, W. Wertelecki, V. Ramesh and J. Gusella
Molecular Neurogenetics Unit, Massachusetts General Hospital, Charlestown 02129.
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.
