Not entirely; you can be born with a gene that makes it very likely that you will develop breast cancer, just as you can be born to be more prone to mental illness. This is the case that I see for homosexuality (keeping in mind that in no way is homosexuality recognised as a disease), that it is probable that there is a genetic factor involved in your eventual sexual development that is present from birth. This wiring in the majority of cases cannot be changed, and in my opinion one should not endeavour to do so.