Mapping the breakpoint of a constitutional translocation on chromosome 22 in a patient with NF2

Clinical manifestations of mutations in the neurofibromatosis type 2 gene in vestibular schwannomas (acoustic neuromas)

Vestibular schwannomas (acoustic neuromas) continue to cause significant facial nerve and hearing morbidity, despite marked improvement in diagnosis and treatment. Mutation of a tumor-suppressor gene on human chromosome 22 has been found to be associated with vestibular schwannoma formation. The central hypothesis of this study is that specific mutations in the neurofibromatosis type 2 (NF2) gene may produce specific clinical characteristics or phenotypic expressions. The purposes of this investigation are: 1. to determine what proportion of vestibular schwannomas from patients with spontaneous unilateral and familial bilateral schwannomas have mutations present within the NF2 gene; 2. to determine whether specific types of mutations are associated with a specific clinical manifestation of this disease; and 3. to further define the relationship between newly discovered mutations within the NF2 tumor-suppressor gene and possible clinical applications of this knowledge to advance diagnosis and treatment of patients with NF2 and spontaneous vestibular schwannomas. DNA from 61 schwannomas (29 unilateral vestibular schwannomas and 32 from patients with bilateral vestibular schwannomas [NF2]) were examined, and 33 unique mutations were identified. Significant differences were found in the frequency, distribution, and type of mutation between the NF2 schwannomas and the spontaneous vestibular schwannomas. Three clinical subtypes of NF2 were identified. In tumors from 28 patients, no mutations were identified. Of the 33 mutations identified in the NF2 gene, 30 were likely to result in loss of tumor-suppressor function from protein truncation; however, three milder mutations termed missense mutations were associated with milder clinical manifestations of the disease and had a slower estimated growth rate. Variable clinical presentation in patients whose tumors had severe or truncating types of mutations suggest that factors in addition to the mutation class are likely to be responsible for a portion of the clinical expression of disease. New diagnostic options are now available for NF2 that will improve the likelihood of hearing and facial nerve preservation and ultimately have significant impact on the management of vestibular schwannomas.

Neurofibromatosis 2 and neurilemmomatosis gene are identical

Neurofibromatosis 2 (NF2) is an autosomal dominant disorder characterized by the occurrence of bilateral acoustic neuromas, as well as meningiomas and schwannomas. The gene locus for NF2 resides on chromosome 22q12 and has been cloned recently. Neurilemmomatosis is characterized by multiple cutaneous and spinal neurilemmomas without other signs of NF1 or NF2. Many cases with this disorder include the diagnosis of neurofibromatosis or other rare diseases unexplained by current nosology. In this study, we analyzed the peripheral leukocytes and tissue from cutaneous neurilemmomas of seven patients with neurilemmomatosis using DNA markers for different regions of chromosome 22. We detected allelic losses in three of seven tumors from seven patients with a probe for the NF2 region of the long arm of chromosome 22 and the germ-line mutations in two of three tumors from the same three patients. Mutations in the NF2 gene were a deletion from at least codon 334 to 579 and G insertion at codon 42. We conclude that the neurilemmomatosis locus lies within the NF2 region and that these diseases might be identical.