Neuropathological and Molecular Features Associated With a Heterozygous <i>DNAJC7</i> Mutation in Amyotrophic Lateral Sclerosis

AIMS: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with unclear molecular mechanisms. Heterozygous protein-truncating variants of DNAJC7, which encode a cochaperone involved in Hsp70/90-mediated protein quality control, are potential risk factors for ALS. However, the neuropathological consequences of heterozygous DNAJC7 mutations are unclear. We aimed to clarify the molecular and neuropathological features associated with a heterozygous DNAJC7 mutation in ALS. METHODS: We genetically screened 39 Japanese patients with ALS and identified a novel heterozygous frameshift mutation in DNAJC7 (c.157_163del, p.Lys53Ter) in one patient that was neuropathologically diagnosed with Kii ALS. We performed biochemical and neuropathological analyses using postmortem tissues from this patient, from cases of ALS without the mutation and from control cases. RESULTS: In the cases of ALS without DNAJC7 mutation, there was elevation of both DNAJC7 mRNA and protein levels compared with controls. The patient with DNAJC7 mutation showed relatively lower DNAJC7 mRNA and protein levels compared with the nonmutated cases of ALS, although mRNA expression remained relatively higher. DNAJC7 may be upregulated as a protective response against ALS pathogenesis, whereas a heterozygous mutation may attenuate this response. Immunohistochemistry and double immunofluorescence demonstrated partial colocalization of DNAJC7 with phospho-TDP-43-positive neuronal cytoplasmic inclusions, which supports a direct role for DNAJC7 in modulating pathological TDP-43 aggregation. CONCLUSIONS: These findings provide neuropathological evidence linking heterozygous DNAJC7 mutation to ALS, demonstrating impaired protein expression and suggesting a loss-of-function mechanism that compromises protective responses to TDP-43 pathology. DNAJC7 may represent a key modulator of ALS pathogenesis and potential therapeutic target.