Genetic and Pathological Assessment of hnRNPA1, hnRNPA2/B1, and hnRNPA3 in Familial and Sporadic Amyotrophic Lateral Sclerosis

Background: Mutations in the genes encoding the heterogeneous nuclear ribonucleoproteins hnRNPA1 and hnRNPA2/B1 have been reported in a multisystem proteinopathy that includes amyotrophic lateral sclerosis (ALS) and inclusion body myopathy associated with Paget disease of the bone and frontotemporal dementia. Mutations were also described in the prion-like domain of hnRNPA1 in patients with classic ALS. Another hnRNP protein, hnRNPA3, has been found to be associated with the ALS/frontotemporal dementia protein C9orf72.

Objective: To further assess their role in ALS, we examined these hnRNPs in spinal cord tissue from sporadic (SALS) and familial ALS (FALS) patients, including C9orf72 repeat expansion-positive patients, and controls. We also sought to determine the prevalence of HNRNPA1, HNRNPA2B1, and HNRNPA3 mutations in Australian ALS patients.

Methods: Immunostaining was used to assess hnRNPs in ALS patient spinal cords. Mutation analysis of the HNRNPA1, HNRNPA2B1, and HNRNPA3 genes was performed in FALS and of their prion-like domains in SALS patients.

Results: Immunostaining of spinal motor neurons of ALS patients with the C9orf72 repeat expansion showed significant mislocalisation of hnRNPA3, and no differences in hnRNPA1 or A2/B1 localisation, compared to controls. No novel or known mutations were identified in HNRNPA1, HNRNPA2B1, or HNRNPA3 in Australian ALS patients.

Conclusions: hnRNPA3 pathology was identified in motor neurons of ALS patients with C9orf72 repeat expansions, implicating hnRNPA3 in the pathogenesis of C9orf72-linked ALS. hnRNPA3 warrants further investigation into the pathogenesis of ALS linked to C9orf72. This study also determined that HNRNP mutations are not a common cause of FALS and SALS in Australia.