Familial amyotrophic lateral sclerosis with a novel G85S mutation of superoxide dismutase 1 gene: clinical features of lower motor neuron disease

Abstract

Amyotrophic lateral sclerosis (ALS) is a devastating disease characterized by upper and lower motor neuron damage. Mutations of Cu/Zn superoxide dismutase gene (SOD1) account for 20% of familial ALS (FALS). We report a unique clinicogenotype of a Japanese family with a novel SOD 1 mutation. A 37-year-old woman (the proband) noticed muscle weakness in the left lower limb. Her mother had developed progressive lower motor neuron signs in four extremities at 38 years of age. Subsequently she was diagnosed as ALS and died of respiratory failure at 15 months after clinical onset. Neurological examination of the proband showed absent muscle stretch reflexes in the left knee and the left ankle without Babinski signs. Mild to moderate degree of muscle weakness existed in the left lower extremity. Muscle atrophy was presented in the left thigh. Initial pulmonary function revealed forced vital capacity of 91.1%. Electromyography disclosed ongoing denervation muscle potentials in the left lower extremity. SOD1 analysis demonstrated amino acid substitution of glycine by serine at codon 85 (G85S) in exon 4. Six months later, marked muscle weakness and atrophy expanded to four extremities. All muscle stretch reflexes were absent. Three months later, ventilator support with a tracheostomy was needed. The patient died at 18 months after clinical onset. Clinical hallmarks of this FALS family indicate that G85S mutation of SOD1 may cause rapidly progressive form of pure lower motor neuron signs.