As Plattys are livebearers like Guppys and Mollys when the fry are born they are folded in half! As they drop into the tank they then flip open to their normal shape.
Unfortunately even without inbreeding and other genetic reasons sometime the fish do not always fold out corrrectly and they then end up with bent spines.
They are otherwise normal fish.
I am with MM when it comes to 'Special Needs' fish. I have Zig and Zag in my community tank as if I had taken them to the
LFS with the rest of thier spawn I knew they would end up in the feeder tanks so they are living happily as members of our family tank.
They will have shortened lives probably but they seem happy and healthy enough at the moment.