Which inherited disorder involves the kneecap slipping out of place?

The condition that involves the kneecap slipping out of place is known as a "slipping kneecap," or patellar luxation. This is an inherited disorder that affects the positioning of the kneecap (patella), causing it to move out of its normal groove in the femur. This misalignment can lead to pain, difficulty in mobility, and long-term joint issues if not addressed.

In contrast, the other options refer to different conditions: hip dysplasia involves a malformation of the hip joint, collie eye affects vision due to abnormalities in the retina, and progressive retinal atrophy (PRA) is a degenerative eye disease leading to blindness. Each of these conditions involves different anatomical structures and mechanisms of disease, further highlighting that the slipping kneecap is distinct and specific to joint mechanics of the knee.