COQ7-Related Juvenile-Onset Motor Neuronopathy: A New Pathogenetic Dysfunction Associated with Motor Neuron Disease

Abstract

A 38-year-old Brazilian man presented with slowly progressive quadriparesis since age 11 years. He progressed over 15 years with symptoms restricted to the lower limbs, and since then, with a progressive compromise of the upper limbs. His deceased brother had a similar clinical presentation. Examination showed spastic dysarthria, global amyotrophy, brisk tendon reflexes in the lower limbs, symmetrical quadriparesis, and fasciculations in the four limbs. Neurophysiological studies disclosed acute and chronic signs of denervation and chronic reinnervation involving the cervical, thoracic, and lumbosacral myotomes, with normal sensory conduction study. Fibrillation potentials, fasciculations, and positive sharp waves involved mainly the upper limbs. A diagnosis of long-standing juvenile-onset motor neuronopathy was established. Genetic testing identified the possibly pathogenic variant c.3G>T (p.Met1?) in homozygosity in the COQ7 gene. This report highlights the importance of considering a potentially treatable metabolic dysfunction as the primary mechanism in cases of juvenile motor neuron disease.