Warning: Some of the images linked in this post may be upsetting

Spina Bifida: NHS Choices | Spina Bifida: Wikipedia (warning for medical images)

What is Spina Bifida? - Spina bifida is a birth defect where there is incomplete closing of the backbone and membranes around the spinal cord. There are three main types: spina bifida occulta, meningocele, and myelomeningocele.

Medical Diagram showing the three types of Spina Bifida

For lions, Spina Bifida would be a lethal mutation. I know people born with this can survive, but that is only with round the clock care and surgery. These are lions - unfortunately, nothing would help them. Spina Bifida cubs would die after their first rollover, like Cyclopia, due to the open wound on the spine.

Appears: At birth
Affects Gameplay?: Yes, cub dies at 1 month
Lethal?: Yes

TL;DR. Spina Bifida, lethal mutation. Cub dies at 1 month old. Cub would be shown lying with it's back facing towards you, the user, with the hole in the spine visible. Would be very rare.

Note: Spina Bifida also comes hand in hand with hydrocephalus, but this would be treated as separate from hydrocephalus if both were implemented.

MUTATION SUGGESTIONS:
[YOU ARE HERE] | Club foot | Osteogenesis Imperfecta [lethal]
EYE SUGGESTIONS
Fruits for the Eyes | Assorted Eyes | Assorted Eyes: Part 2
MARKING SUGGESTIONS
November and Gem Markings | February and Gem Markings
Rosette Recolours | Giraffe and Inverted Giraffe
BASE SUGGESTIONS
Cake's Realistics | Cake's Semi-Realistics
Cake's Unrealistics | Cake's Combos
GENERAL SUGGESTIONS
Spoiler Button | Event Based Site Themes