Background: Idiopathic normal pressure hydrocephalus (iNPH) is usually regarded as a disease characterized by gait and balance disturbance, cognitive dysfunction, and urinary symptoms. The pathophysiology of iNPH is still unknown, but the increased number of familial cases raises the suspicion of a genetic component. The C9ORF72 expansion is known to cause frontotemporal lobar degeneration and ALS, and its prevalence is found among Finnish iNPH patients. Case Presentation: We report an interesting case of a patient with possible iNPH who also developed ALS. Conclusion: Our case raises the theory of coexistence of gene-induced etiology. Key Message: Our case also raises the question of a genetic link between iNPH and ALS.

Keywords: Idiopathic normal pressure hydrocephalus, familial, C9ORF72 expansion, ALS