Sorry if this has been suggested before. I checked and didn't see anything about it ^^|||

MBD, metabolic bone disease, for lions.
I got this idea from here
George suffers from MBD, and due to it, he walks weirdly.

MBD can refer to any bone disorder, like osteoporosis, osteomalacia, etc etc.
"Most commonly these disorders are caused by abnormalities of minerals such as calcium, phosphorus, magnesium or vitamin D leading to dramatic clinical disorders that are commonly reversible once the underlying defect has been treated." But, since these are lions, it can't be treated well.

I was thinking it could:
Cut sub male patrols/lioness hunting in half
Can't be kinged (maybe)
Fails a lot for cub training
Playing/tussling could give messages, or just visiting their page would

The legs would look wonky, kinda like George's legs.
And he mentions that George is smaller than he should be, so maybe the lion could look a tad bit smaller (though I highly doubt it).

During the video, when loading back into the truck, George cannot jump in, and needs Kevin's assist.

MBD does occur in animals (mainly reptiles), and lions have been reported with such disorders. I suggested the lions having weird looking legs because it's the easiest way to show the disease, in my opinion.

--If you have any suggestions, or reasons why you don't support, please share! I love to hear feedback, and I'm not the best at expressing my ideas ^^|||

Images (trypophobia warning for the first link):
Bone Compare
Info
More Info

I also got this idea from my bearded dragon, Mythra, who also suffers from MBD, which you can see that the base of his tail is swollen, his tail won't fully grown, an underbite, and on one hand he walks with his wrist.
He's getting much better though, and I've been giving him special diets to help him. His tail most likely won't heal, but he's able to walk normally again. His underbite has not affected is eating whatsoever.

Thank you for reading ^^

Suggestion(s):
Silverfire: "I think that this would be better as a lethal mutation."

fortmax: "Also support as lethal + without ability to be kinged!" + "It's also fair to mention that this is NOT VERY RARE- this occurs in many species as an acquired disorder ie in reptiles or amphibians from lack of nutrition, as you mentioned with your beardie. So, this could be a more common lethal (AMONG LETHALS- it would still be a rare mutation, but less rare than, say, Cyclopia)"