[A young woman with a weakening leg]

SOD1 mutations account for less than 25 % of cases with familial amyotrophic lateral sclerosis and may cause atypical phenotypes.

A young woman developed progressive right ankle paresis that made running difficult after two years. Neurological examination revealed flaccid paresis of the right calf without fasciculations or sensory deficits. Electromyography displayed evidence of denervation restricted to the right calf. Sequencing of the SOD1 gene revealed an A > G mutation in nucleotide position 140, that causes substitution of arginine with histidine in amino acid position 46 (H46R). The patient's father had developed similar symptoms at the age of 60 but was still ambulant 5 years later. The patient's grandmother developed similar symptoms aged 40, and used a wheelchair for several years before she died in her nineties. None of the affected family members developed overt arm or bulbar pareses.

The H46R SOD1 mutation in this case of familial amyotrophic lateral sclerosis causes a slowly progressive lower motor neuron disease that remains restricted to the legs for years or even decades.