There was one acronym in the book, FA, which is mentioned in the book on his first call with Sally. Which according to google is Friedreich ataxia. But maybe this acronym means something else, I'm not sure!
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(view spoiler)[It took me a minute, too, and I had to go back and re-read his phone conversation with his sister. She mentions there that she has heart problems like their dad did, so she died from some kind of heart condition. (hide spoiler)]