Old age creeps in slowly for the young adult. Sudden changes may take place for the old, however. The old person becomes forgetful. At first it becomes a matter for laughter and joke in the family. Soon one notices that the old person is more confused than ever. He has more frequent mood changes, and begins to act in strange ways. He forgets the names of people around him, names of his own children and grandchildren whom he loved deeply. He begins to suspect your motives and wants to avoid you. Soon the old person becomes a different person altogether. He does not know his name, does not recognize his environment, and does not recognize his family. He is a stranger in his own family. He leaves home at his will and does not know where he goes or how he could return home. Family members are greatly worried and do not know what to do. The disease progresses rather slowly.
The Alzheimer's disease was not recognized as a devastating one until the 1980s. But, since then, we read about it almost daily, and come across people and families that have been affected by it. The German doctor Alois Alzheimer described the disease somewhat definitively in 1912, I think. The disease is named after him.
In India and South Asian nations, cultural traditions took the onset of senility as a natural process of aging. Since life expectancy was rather short in these nations until a few decades ago, the Alzheimer's disease was assumed to be an occurrence or the phenomenon of the Western materialistic nations. There is a greater recurrence of this disease now noticed in India, especially among the people of middle classes.
In terms of Indian languages, the pronominal usage is much affected, at variance with what the person would have done if he were not an Alzheimer's patient. The verb inflection with appropriate pronoun endings is also affected. He has problems with number and person attached to the main verb, but his problem with the gender is not as intense as his problem with the number and person of his addressee.