what would you do in a family that values older siblings more then the younger one?

Growing up in a family that does I can tell you it sucks. When I was the young age of seven my family decided that since I was the younger then my sister I wasn't qualified to be smarter. My sister , whom I love dearly, never knew the struggle of constantly being put down for doing great in school. Weird right? Usually parents praise their kids for doing good in school. Well mine did but only if I did worse then my sister.

To put this in perspective my sister was diagnosed at a young age with a type of disease that affects her nerves and joints. She couldn't stand to be touched ,nor could she stand to walk due to the extreme pain. They said she would be physically and mentally retarded ..

Well when she was around 5 years old she was introduced to an experimental drug that would allow her to walk . She took this among nearly 20 other medications. My sister is not to be blamed because she can't help that she was sick ,but our parents thought since she is the oldest she must be the smartest .

My teachers often complimented on how naturally gifted I was in school much to my parents dismay. I was seven being told that I need to slack off so my sister would be looked down upon. She's a year older and in the same grade as me. So my the time we were in the fifth grade I had enough my teachers yelling at me that I'm smart and am wasting my potential on one hand and on the other my parents yelling I'm bringing shame to my sister. So I purposely caused my near perfect 3.9 gpa to drop to a drastic low of 2.1.

To give you an idea of what that is; imagine a near straight A student making straight D's on purpose. I was emotionally tired of constantly being yelled at for doing good only to be constantly yelled at for doing terrible.

What would you do?