SMARCB1 and schwannoma: More likely, as suggested by Hadfield et al. [380], a three-step model of schwannoma development, comprising the biallelic loss of SMARCB1 and loss of one NF2 allele mediated by 22q deletion, would serve to accelerate Schwann cell proliferation thereby driving the somatic intragenic NF2 PV that represents the third step.