Hi,
If he talks to his GP on his concerns there should be further tests his GP can do for him - I know some GPs aren't great when it comes to prevention / forward planning etc, but it's up to him to push it if he has concerns... Have a read of:
[broken link removed]
I have no connection with this place - just used it for reference before when chatting to my GP. If further tests are carried out by GP, then expect to pay extra as more time will be needed to run such.
Make sure he goes through ALL family medical history .... siblings, parents, parents siblings, grandparents - try to see what they may have, (e.g. diabetes in the family) - have that list together before he meets with GP / specialists...