Amyotrophic lateral sclerosis (ALS), also called Lou Gehrig Disease, is a degenerative neuromuscular disorder. Up to 5-10% are inherited.

Early symptoms are weakness, that usually is more prominent in the lower extremities (legs) - but this is highly variable. In some patients the motor cranial nerves (bulbar palsy) are affected earlier. They present with swallowing difficulty and abnormal eye movements/diplopia.

The disease is relentlessly progressive - but at different rates in different patients. Ultimately, impairment of the respiratory muscles may lead to permanent artificial ventilation or a choice of death.

Incidence is similar to MS, but prevalence is lower due to short lifespan after presentation, typically only 2-5 years. Most patients present in the 5th - 7th decades (40's - 60's). Both upper and lower motor neurons may be affected. Upper motor neuron (UMN) disease presents with hyperreflexia. Lower motor neuron disease (LMN) presents with atrophy, weakness, flaccidity. Fasciculation occur when there is anterior horn cell involvement.

The molecular biology of ALS may be related to abnormal retrograde axonal transport. Like many other neurodegenerative disorders, there is abnormal accumulation of proteins and/or abnormal protein withing the neurons.

The congenital variant has a longer survival in some patient series.

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