<Tr> <Th> Prognosis </Th> <Td> Life expectancy 2--4 years </Td> </Tr> <Tr> <Th> Frequency </Th> <Td> ~ 2.5 per 100,000 per year </Td> </Tr> <P> Amyotrophic lateral sclerosis (ALS), also known as motor neurone disease (MND), and Lou Gehrig's disease, is a specific disease which causes the death of neurons controlling voluntary muscles . Some also use the term motor neuron disease for a group of conditions of which ALS is the most common . ALS is characterized by stiff muscles, muscle twitching, and gradually worsening weakness due to muscles decreasing in size . This results in difficulty speaking, swallowing, and eventually breathing . </P> <P> The cause is not known in 90% to 95% of cases . The remaining 5--10% of cases are inherited from a person's parents . About half of these genetic cases are due to one of two specific genes . The underlying mechanism involves damage to both upper and lower motor neurons . The diagnosis is based on a person's signs and symptoms, with testing done to rule out other potential causes . </P>

What is the full form of als disease