Short Explanation : In short Gastroschisis is a defect in which an infant is born with some of its abdominal organs born outside of its abdomen through a small hole to the right of the infant's bellybutton.

Lengthy Explanation: Gastroschisis is caused when one or both body wall folds within an embryo do not move properly and therefore do not fuse. This incomplete fusion results in this defect that allows the infant's abdominal organs to go through the abdominal wall and outside of the body, through a very small hole to the right of the infant's belly button, or you could just have a hole.

Is it Possible in Lions?: While I was unable to find any evidence during my research that this defect does occur in lions, I know from personal experience, that this defect not only effects human, but also sheep, cattle, dogs, and even cats. I believe that my inability to uncover any evidence on this defect afflicting cats is likely due to the lack of research on Gastroschisis in big cats, as it seems more than possible that big cats also experience this defect.

"Warning! Some viewers might find this image distressing"
I would show pictures of it occurring in other animals, but the pictures are just too graphic. If proof is needed, I can edit in some links to pages that talk about it.

Cub Appearance/Information: Any infant with Gastroschisis will die if left untreated, hence why I believe it should be a lethal defect that kills the cub at 1 month due to infection.

Appearance (Non Graphic): Small sickly looking newborn cub lying on it's side with its belly facing towards the player, and a noticeable hole off centre from its lower belly.
Suggested by: Felicity Smooake #31735

Appearance (Slightly Graphic): I think that it should be a small, sickly looking cub lying on its side, with its belly facing towards the player, and a small hole in its belly with perhaps a small bit of intestine poking through the hole.