What Are Motor Neuron Diseases (MNDs)?

Motor neuron diseases (MNDs) are progressive neurological conditions that damage nerve cells known as motor neurons. Ordinarily, upper motor neurons in the brain transmit messages to lower motor neurons in the brainstem and spinal cord; the lower motor neurons then transmit these signals to the muscles to produce muscle movement. MNDs destroy motor neurons, so this process is disrupted, which affects skeletal muscle activity, such as walking, talking, swallowing or breathing.

Motor neuron diseases are categorized into several types. One of the most well-known types of MND is amyotrophic lateral sclerosis, or ALS.

Signs and symptoms

The signs and symptoms of motor neuron diseases vary depending on the specific disease. However, some of the most common signs and symptoms include the following:

• Loss of muscle control
• Muscle weakness or stiffness in a limb
• Difficulty chewing, speaking or swallowing
• Clumsiness or loss of coordination
• Balance issues

Symptoms may develop slowly, gradually becoming more widespread and severe.

Causes

The cause of most motor neuron diseases is unknown. However, some MNDs are caused by a hereditary gene mutation. Motor neuron diseases can also be sporadic (non-inherited). Environmental, viral, or toxic factors may contribute to the development of sporadic motor neuron diseases, but more research is needed.

Risk factors

Motor neuron diseases can occur at any age. Genetic motor neuron diseases are more likely to develop in children, whereas adults are more likely to experience sporadic motor neuron diseases. The risk factors for MNDs differ depending on the specific type of disease. For example, ALS and primary lateral sclerosis, or PLS, are more common in men than in women and are most likely to develop between the ages of 40 and 60. Furthermore, smoking and exposure to lead or other environmental toxins increase the risk of developing a sporadic motor neuron disease.