RESUMO
BACKGROUND: Multiple meningiomas occur in <10% of meningioma patients. Their development may be caused by the presence of a predisposing germline mutation in the neurofibromatosis type 2 (NF2) gene. The predisposing gene in patients with non-NF2 associated multiple meningiomas remains to be identified. Recently, SMARCB1 was reported to be a potential predisposing gene for multiple meningiomas in a family with schwannomatosis and multiple meningiomas. However, involvement of this gene in the development of the meningiomas was not demonstrated. RESULTS: Five affected members of a large family with multiple meningiomas were investigated for the presence of mutations in SMARCB1 and NF2. A missense mutation was identified in exon 2 of SMARCB1 as the causative germline mutation predisposing to multiple meningiomas; furthermore, it was demonstrated that, in accordance with the two-hit hypothesis for tumourigenesis, the mutant allele was retained and the wild-type allele lost in all four investigated meningiomas. In addition, independent somatically acquired NF2 mutations were identified in two meningiomas of one patient with concomitant losses of the wild-type NF2 allele. CONCLUSION: It is concluded that, analogous to the genetic events in a subset of schwannomatosis associated schwannomas, a four-hit mechanism of tumour suppressor gene inactivation, involving SMARCB1 and NF2, might be operative in familial multiple meningiomas associated meningiomas.
Assuntos
Proteínas Cromossômicas não Histona/genética , Proteínas de Ligação a DNA/genética , Genes da Neurofibromatose 2 , Mutação em Linhagem Germinativa/genética , Meningioma/genética , Fatores de Transcrição/genética , Sequência de Bases , Análise Mutacional de DNA , Primers do DNA/genética , Feminino , Genótipo , Humanos , Masculino , Meningioma/patologia , Repetições de Microssatélites/genética , Dados de Sequência Molecular , Mutação de Sentido Incorreto/genética , Linhagem , Proteína SMARCB1RESUMO
Schwannomatosis is characterized by the development of multiple schwannomas of the nervous system, but without the occurrence of vestibular schwannomas. Most cases of schwannomatosis are thought to be sporadic, representing the first case in a family due to a new mutation in the causative gene. We recently identified SMARCB1/INI1 as a schwannomatosis-predisposing gene. Here, we analyzed this gene in a schwannomatosis family with two affected children, but with clinically unaffected parents. Both affected individuals carried a constitutional SMARCB1 mutation, c.1118+ 1G>A, that changes the donor splice site sequence of intron 8, causing skipping of exon 8 and resulting in the in-frame deletion of 132 nucleotides in the transcript. The mutation was not evident in constitutional DNA of the parents. Haplotyping revealed that the chromosome 22 segment that carries the mutant SMARCB1 allele originated from the mother. She transferred the same chromosome 22 segment, however, with a wild-type SMARCB1 copy, to a third unaffected child. Our findings indicate that the mother is germ line mosaic for the SMARCB1 mutation. In conclusion, our study shows for the first time that germ line mosaicism may occur in schwannomatosis, which has implications for genetic counseling in this disease.
