We found a kitten in the dumpster behind our house a couple weeks ago, we think she's about 5 weeks old now. We think her leg has fallen out of the hip socket. We tried taking her to our vet's but it was closed for the weekend. She's still eating and going to the bathroom. It's just obvious that it hurts her to walk and we can feel a difference between the left hip area and the left hip area, a bump where no bump should be. I was wondering if their were any genetic issues or diseases that would case this in a kitten so young.

Not all joint problems show up later in life. Some can start from birth.

It may be genetic, or it may have something to do with the mother's health during pregnancy. It could also be from something that happened since it was born, or during the birth itself. Only a vet will be able to tell you for sure.

Hopefully, it'll be as simple as the vet popping the joint back into socket and prescribing pain meds for the next week or so. You should also be prepared for the possibility that surgery will be required, or that there's no way to fix the problem.

In the mean time, try hand feeding her. A few pieces of food in your hand at a time, and putting a shallow saucer of water in front of where she's lying, should help. If she doesn't want to eat the food out of your hand, then place it on a saucer. Wetting down dry food with water or a little tuna water (make sure it's water, not oil, that the tuna's sitting in) will make it more appetizing and easier to eat, it'll also get fluids into her. All you can do is make her as comfortable as possible and try to get her to eat, until you can get her to a vet.

Here's a site that may be helpful:
Hip Dysplasia in Cats: Winn Feline Foundation