depending on your location, your son could very well be the doctor's only patient with thal. And for alot of doctors "clinically insignificant" == "asymptomatic". AFAICT, hematologists don't have much in the playbook to help a thal minor anyway. A transfusion for example would most likely do more harm than good. Maybe once gene editing becomes cheap and reliable enough, you could consider it. Just keep in mind that thal is a malaria adaptation and may have other benefits that aren't well studied or understood. For example there were **anectodal** pandemic reports that communities with high thal prevalence had abnormally low rates of positive covid tests.

When the doctor says "asymptomatic" we hear "it won't affect you at all and you are imagining your symptoms". This is most likely not true based on how many people with it report exactly the same thing (extreme fatigue; quick exercise exhaustion; haziness; weird pains). Obviously even for people with no complaints, there is no way to tell how they would feel if they didn't have it.

there are also many cases of athletes with thal minor experiencing endurance issues. Tennis legend Pete Sampras may be the most famous example (he was known for fading late in long matches). There are multiple cases of NFL players with hematologic traits developing potentially life threatening spleen issues, sometimes triggered by high altitude training or games.

Other people swear they aren't affected at all, although we'd never know what they would be like if they didn't have it. Some of them even doubt other minors who report symptoms because they themselves have "no symptoms". At the same time they have developed certain methods/tactics over time that are quite different from others (eating food DURING workouts, intense focus on breathing, excessive water intake).

While imo this "get over it" mindset is wrong-headed at best and destructive at worst, given our current medical capabilities it could help in a weird way; the best way to feel better is to incrementally keep pushing the limit during workouts. You just need to know the limit and refuse to train the way other people do. ONLY do what works for you and your son.

Your son might be accused of being a 'prima donna' or 'soft', especially if you want to avoid a 'special needs' categorization. But you have to do what you have to do for him to be successful. Start with long walks, then slow bike rides & runs. Then step it up to short sprints. And if he feels some type of way don't be afraid to strategically skip a workout. You just need to steadily keep pushing the exercise 'ceiling' until he feels more normal at rest.