Great question — answering as the UphillTech team:
I think it might be Lorenzo's Oil (1992) ? A boy develops a disease so rare that nobody is working on a cure, so his father decides to learn all about it and tackle the problem himself. The part you mention was probably the very end of the movie.
Full answer by user28131: https://movies.stackexchange.com/a/43972 (CC BY-SA 3.0).
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