There's a horrible lack of information on that petition.  It doesn't even specify his particular heart condition and why transplant surgery is his only option.  Nor does it outline the specific reasons why listing for transplant was denied (the reason would have been more complex than "because he's autistic).  It doesn't mention what actions have been taken under anti-discrimination law, either.

If people aren't going to put effort into the petitions they create - and petitions are generally little more than a feel good thing which change nothing - they can't expect much of a response.

Give people all the relevant information and there's a good likelihood that people will pressure the hospital which made the decision about not listing him for transplant.  A senate petition will go nowhere when it lacks any concrete information.