The rare G93D mutation causes a slowly progressing lower motor neuron disease.

We describe an ALS family with the rare SOD1 G93D mutation. Three members of the family developed ALS at an age ranging from 45 to 71 years. In all cases pyramidal signs were not evident. Two members of the family were obligate gene carriers, and died at 56 and 81years, respectively, without developing ALS signs or symptoms. The mutation was found in the DNA extracted from the hair bulbs in the two deceased obligate carriers and in another family member who died at 80 years of age without any sign of the disease. This study shows that SOD1 G93D mutation causes a slowly developing lower motor neuron disease with a reduced penetrance.