Similar Allele Frequencies of Two Pathogenic NF2 variants in Each of Nine Sporadic Vestibular Schwannomas

Background/Aim: Vestibular schwannomas are benign tumors on the vestibular nerve caused by bi-allelic inactivation of the NF2 tumor suppressor gene. This study identifies sporadic vestibular schwannomas with two pathogenic NF2-variants in each of them and compares the allele-frequencies of the two variants. Patients and Methods: Sporadic vestibular schwannomas were subjected to genetic analysis regarding pathogenic variants in the NF2 gene using targeted sequencing. Cases with two different pathogenic NF2 variants were identified and the allele-frequencies of the two variants in each tumor were compared. Results: Nine tumors were identified which had two different pathogenic NF2 variants in each of them. For all the 9 tumors, the allele-frequencies of the two pathogenic NF2 variants in each were nearly identical. Conclusion: This finding may indicate that the two inactivating NF2 variants occurred shortly after one another, leaving no room for the Schwann cells with one inactivating NF2 variant to expand. Alternatively, the variants occurred in a late development stage whereas Schwann cells do not expand anymore or expand only extremely slowly. In addition, our finding suggests that Schwann cells with one inactivating variant do not gain a growth advantage.