Tracing neuropathological signatures: TARDBP and C9orf72 double mutations in a Sicilian family.

Co-occurrence of double heterozygosity in TARDBP and C9ORF72 is exceedingly rare in amyotrophic lateral sclerosis. While TARDBP mutations and C9ORF72 hexanucleotide repeat expansions have each been independently implicated in disease pathogenesis, their combined effect on disease progression and neuropathology remains unclear. We present the first study documenting a patient harboring both a TARDBP mutation and a C9ORF72 expansion, with comprehensive postmortem data available, to elucidate any additive or synergistic effects on disease course and pathological burden. Detailed clinical assessments tracked the patient's progression, and neuropathological examination was performed postmortem. The presence and extent of TDP-43 pathology and other hallmark features were evaluated and compared to known patterns in carriers of isolated C9ORF72 mutations. The patient's clinical trajectory and pathological findings did not show evidence of a more aggressive disease course or heightened pathological burden attributable to the additional TARDBP mutation. Instead, the disease manifested in a manner consistent with other C9ORF72 carriers, suggesting that double heterozygosity do not necessarily exacerbate ALS pathology.