I just googled homocystinuria, from what I can tell it is a metabolic disorder, which shouldn't affect your fertility I don't think, but it is a genetic disorder, which means you have a 1 in 4 chance of passing on the gene to your offspring. But it is a RECESSIVE disorder, so they would only be a carrier of the disease unless they got another copy of the same defective gene from their father. It obviously varies in severity (as you didn't even know you had it?) but I would be asking to speak to a genetic counsellor just to ease any fears and answer any questions you may have. Your FS should be able to give your more specific advice regarding any effects on fertility.