Answer:
Neurodegeneration
Explanation:
The term neurodegeneration refers to a group of disorders which are characterized by a progressive waste of function or structure of neurons, that in worst cases can include death of neaurons.
Many neurodegenerative disorders such as Parkinson's disease,– including amyotrophic lateral sclerosis, Huntington's disease and Alzheimer's disease can occur due to neurodegeneration.
Neurodegeneration can manifest itself in various forms such as lack of physical and intellectual abilities like inability to use muscles or memory loss. These disorders cannot be completely cured and ultimately lead to the death of neurons.
As mentioned in the question, the person suffers from progressive loss of intellectual and physical abilities that has occurred over the course of a long period of time. Therefore, it is most probable that he is having some neurodegenerative disorder.
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