A novel homozygous loss-of-function variant in SOD1 causing progressive spastic tetraplegia and axial hypotonia

SOD1 is the first identified causative gene for amyotrophic lateral sclerosis. Recently, a novel syndrome, presenting with severe childhood-onset spastic tetraplegia and axial hypotonia caused by the homozygous truncating variants in the SOD1 gene, is described. A 22-month-old boy was admitted with a loss of motor functions that began at the age of 9 months. Neurological was significant for axial hypotonia with spastic tetraplegia and hyperekplexia-like jerky movements. In WES, we found a novel homozygous variant (c.52_56del5ins154) in the SOD1 gene, resulting in a total loss of SOD1 mRNA expression in the real-time PCR analysis. Western blot analyses confirmed the lack of protein production. Erythrocyte superoxide dismutase enzymatic activity was nearly abolished. The heterozygous family members displayed reduced superoxide dismutase 1 protein expression and enzymatic activity (by about 40%), compared with the healthy control. Our study expanded the mutation spectrum of SOD1.