MNDs are a group of progressive neurological disorders that destroy motor neurons, the cells that control skeletal muscle activity such as walking, breathing, speaking, and swallowing. This group includes diseases such as amyotrophic lateral sclerosis, progressive bulbar palsy, primary lateral sclerosis, progressive muscular atrophy, spinal muscular atrophy, Kennedy's disease, and post-polio syndrome.

The research team used genetic sequencing techniques to investigate the genome of three families with individuals affected by hereditary spastic paraplegia -- a large group of MNDs in which the motor neurons in the upper part of the spinal cord miscommunicate with muscle fibers, leading to symptoms including muscle stiffness, weakness, and wasting.

The researchers found that changes in the transmembrane protein 63C (TMEM63C) gene were the cause of the disease, while further bolstering the hypothesis that MNDs are caused by abnormal processing of lipids including cholesterol.