Hello Doctor. My Name Is Ketan I Am From Ahmadabad

Hello Doctor.
My name is ketan I am from Ahmadabad India.
My father is diabetic patient from long time and now from two three years he facing problem regarding taste less tongue. What ever he eat he don't feel any taste on his tongue.
He went to many doctors but still he has same problem

So I would like to know reason behind this and what kind of treatment he should follow.

Thanks & Regards
Ketan Deore
091 0000
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