Hi crystal, i've had this condition since I was a kid and I understand this is more common than you would think (in the uk anyway). Most cases are the result of testicular cancer in later life, but it can occur for a variety of reasons, in my case it was due to complications at birth and a bunch of bungling doctors. Something similar occurs in women as well, but is more to do with the pituitary gland in those cases (well, you'd hope so anyway :) ).
I dont know what the details are of your boyfriends condition, but i'll try to help with the little info i've got.
There isnt, unfortunately, a lot of info widely available about the condition, but I can answer a couple of questions. In regards to his life expectancy I wouldnt worry about that too much, people with this condition are only at serious risk of reduced life expectancy if they develop the condition young (pre puberty) and arent treated, and then most of the risks are a result of poor development, i'm guessing your boyfriend didnt have this condition young and matured normally, so he should be fine. As far as I can tell in your boyfriends case he would be physically ok even without treatment but it would screw up his quality of life. I havent come across any definite complications in the future so long as treatment is given.
The medication he takes is an "androgen" and there are a bunch of treatments available, the medication I use is called andropatch and is a daily patch that delivers through the skin, I had those fortnightly injections for years and man did they suck, your boyfriend has my sympathy. You can find some info on these here:
Drugs.Com/cons/depo_testosterone_cypionate
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i understand if sufferers dont get treatment later in life they have an increased risk of osteoperosis, I think the risk is minimised if treatment is given.
Speaking from my own personal perpsective this condition is not great. While there are few health risks I have found that the condition can cause depression and tiredness, I find there are mixed opinions on this in the medical profession, but I find I tire easily and am inclined to feel tired, anxious and generally miserable a lot of the time. This may or may not be the case with your boyfriend, so long as he gets plenty of exercise (and some calcium and vitmain d to help against osteoperosis) and has his friends and family around him for support he should be ok.
I hope this helps. It may be worth talking to your doctor to see if there is any further information they can give.
Nick