[The genetics of corticobasal syndrome]

Corticobasal syndrome (CBS) is a clinical syndrome presenting with progressive asymmetric bradykinesia, rigidity, and dystonia accompanied by cortical signs, such as apraxia, alien limb phenomena, cortical sensory loss, myoclonus, and mirror movements. CBS is associated with different pathological conditions including FTLD-tau (corticobasal degeneration, CBD; progressive supranuclear palsy, PSP: and Pick disease), FTLD-TDP, Alzheimer disease, Creutzfeldt-Jakob disease, and Parkinson disease/dementia with Lewy bodies. Among these, the most common pathology is CBD. In patients with familial and sporadic FTLD, MAPT, GRN and C9orf72 mutations are the three main causes of the disease, even though the C9orf72 mutation is rare in Japan. Patients with MAPT mutations present with FTLD-tau, and patients with GRN and C9orf72 mutations exhibit FTLD-TDP. FTLD is also associated with VCP, CHMP2B, TARDBP and FUS mutations, but each of these account for <1% of familial FTLD cases. In sporadic cases, the H1c haplotype and the rare p.A152T variant of MAPT are known to be associated with FTLD-tau, and the common genetic variant (rs5848) in the 3'-UTR of GRN is associated with FTLD-TDP. A recent genome-wide association study identified TMEM106B as a potential risk-modifying factor for FTLD-TDP, and STX6, EIF2AK3 and MOBP, for PSP. Despite major advances in genetic studies in recent years, the majority of sporadic CBS cases are genetically unsolved. Further studies are needed to unveil the genetic background of CBS. In this review, we discuss the recent advances related to the genetics of CBS, particularly about the genetics of FTLD.