What Causes Motor Neuron Diseases?

What are motor neuron diseases?

Motor neuron diseases (MNDs) occur when motor neurons, or nerve cells that control movement, become damaged and die. MNDs are either hereditary or sporadic. “Sporadic” means that the disease is not inherited. Some types of motor neuron diseases are more likely to be hereditary than others.

Hereditary motor neuron diseases

Hereditary motor neuron diseases are usually caused by mutations in a single gene (the specific gene varies depending on the type of MND) that is passed down from one generation to the next. Only a small percentage of motor neuron diseases are hereditary. For example, only 5% to 10% of amyotrophic lateral sclerosis (ALS) cases are genetic.

Motor neuron diseases that are always inherited include spinal muscular atrophy and Kennedy’s disease. Kennedy’s disease affects only males, but females can be asymptomatic carriers of the disease.

Sporadic motor neuron diseases

When a motor neuron disease does not have a genetic cause, it is considered “sporadic.” Sporadic motor neuron diseases are more likely to occur in adults than in children. The exact cause of sporadic MNDs is unknown.

Scientists suspect that one or more of the following environmental factors may contribute to the development of sporadic motor neuron diseases:

• Exposure to toxic or infectious agents
• Viruses
• Physical trauma
• Behavioral or occupational factors (For example, veterans and athletes may be more likely to develop ALS.)
• Diet

These environmental factors have not been proven to be the cause of sporadic MNDs; therefore, research is ongoing.