Off‐Label Treatment of 4 Amyotrophic Lateral Sclerosis Patients With 4‐Aminopyridine

Amyotrophic lateral sclerosis (ALS) is a fatal disorder characterized by degeneration of the upper and lower motor neuron. Among the at least 25 known genes associated with familial (hereditary) and sporadic ALS, mutations in fused‐in‐sarcoma (FUS) and superoxide dismutase 1 (SOD1) have been extensively investigated in the past years, with emphasis on altered excitability of affected neurons. Recently, we reported on hypoexcitability and increased cell death in a FUS/SOD1‐ALS–induced pluripotent stem cell–derived motor neuron model, which was partly reversible by a treatment with the potassium channel blocker 4‐aminopyridine (4‐AP). Based on this study, we aimed to examine this US Food and Drug Administration–approved drug as a potential individualized treatment for patients with ALS. We therefore retrospectively investigated 4 FUS/SOD1‐ALS patients who were prescribed 4‐AP. Two patients expressed an improved quality of life due to regain of facial muscle motor function and decreased disease progression rate, respectively. Together with recent pathophysiologic findings, this case series supports the need for clinical trials to examine the efficacy of this potential treatment in distinct ALS subgroups and disease stages.