My parents (67M, 68F) is forcing me (25M) to leave my gf (25F) solely because of her medical condition. What should I do?

Me (25M) and my gf (25F) has been together for more than 6 years. We survived long-distance relationship for the first 3 years and had a amazing relationship for the subsequent 3 years. She is my best friend, close confidant and we cannot imagine our lives without each other. We rarely ever argues and our personality complements each other, and our friends too always said we are a perfect couple. Essentially, she's the perfect one for me.
Initially, my parents loved her a lot too. They always showered her with gifts and really supported us being together. In fact, my parents had been nagging us to get married soon.
However, my gf is a carrier of BRCA-2 gene mutation, which means, she will be at a higher risk of getting breast cancer and ovarian cancer in the future.
I am well aware of her condition and am ready to support her and walk with her, as her future husband. We planned everything we needed to do: such as getting IVF done to prevent the gene from being passed down and her getting her breasts removed to prevent cancer from developing.
Unfortunately, I decided to tell my parents about my gf's gene mutation, hoping to get their understanding and support. However, they did not take it lightly. My mom threw a massive fit and demanded me to leave my girlfriend immediately. Essentially, they don't want my girlfriend to be "imperfect" and they don't want me to potentially suffer from taking care of my gf in the future such as bringing her to hospital appointments and stuff. They also said that the costs of IVF and her treatment can be too expensive (even though we have medical insurances already) and denied us together.
My girlfriend had been really heartbroken because of this but she's still willing to put up with my parents if it means us getting married and be together.
Today, my mom has placed an ultimatum on me: either leave my girlfriend or be disowned by them (I am their only son btw). I love my girlfriend too much and I can't imagine breaking up with her. I also do feel it is way too cruel to leave my girlfriend JUST because of her genetic predisposition to cancer.
So, I don't know what to do. Any advice will be appreciated!
TL,DR: my gf and I had a 6-year strong relationship together and my parents loved her. But my gf has a genetic mutation that places her at higher risk of getting cancer in the future. Now my parents is asking me to either leave her just because of her cancer risk or be disowned by family. What should I do?


Source.

It's up to you not your parents I would choose your girlfriend over parents especially when you guys are a perfectly fine couple even with your gfs disability sorry to hear about that but the last choice is your choice and if you really love your fiancee then there should be no problem 👍 if your parents can't handle it then tell them they don't deserve to have you around and just leave good luck n I'll pray for you and your fiancee