Expanding the spectrum of annexin A11 proteinopathy in frontotemporal lobar degeneration and motor neuron disease

Aggregation of TAR-DNA-binding protein 43 (TDP-43) is strongly associated with frontotemporal lobar degeneration (FTLD-TDP), motor neuron disease (MND-TDP), and overlap disorders like FTLD-MND. Three major forms of motor neuron disease are recognized and include primary lateral sclerosis (PLS), amyotrophic lateral sclerosis (ALS), and progressive muscular atrophy (PMA). Annexin A11 (ANXA11) is understood to aggregate in amyotrophic lateral sclerosis (ALS-TDP) associated with pathogenic variants in ANXA11, as well as in FTLD-TDP type C. Given these observations and recent reports of ANXA11 variants in patients with semantic variant frontotemporal dementia (svFTD) and FTD-MND presentations, we sought to characterize ANXA11 proteinopathy in an autopsy cohort of 379 cases diagnosed with a primary TDP-43 proteinopathy, including FTLD-TDP, FTLD-MND, and MND-TDP. Cases with FTLD-MND and MND-TDP were classified further into PLS, ALS, and PMA based on the relative loss of upper and lower motor neurons. ANXA11 proteinopathy was present in over 40% of FTLD-MND cases. Further, ANXA11 colocalized with TDP-43 in the pathologic inclusions of all FTLD-TDP type C cases, as well as 38 out of 40 FTLD-PLS cases (95%), of which 84% had TDP type B or an unclassifiable TDP-43 proteinopathy and 16% had TDP type C. Genetic analysis excluded pathogenic ANXA11 variants in all ANXA11-positive cases. We thus demonstrated two novel ANXA11 proteinopathies strongly associated with FTLD-PLS, but not with TDP type C or pathogenic ANXA11 variants. Given the emerging relationship between TDP-43 and ANXA11 in neurodegenerative disease, we propose that TDP-43 and ANXA11 proteinopathy (TAP) comprises a distinct group of molecular pathologies and define three TAP types based on key clinical and neuropathologic characteristics.