Piebald Spider Ball Python
One animal carrying both genes. Each one is inherited separately, so this combination is made by bringing them together rather than being a gene of its own.
Documented health finding on one of these genes
Spider. Animals carrying this gene are widely documented to show a neurological head wobble, ranging from barely detectable to severe. It is associated with the gene itself rather than with husbandry, and every animal carrying it is considered affected to some degree.
The two genes
How one is made
Both genes have to come together in the same animal. The pairing that does it most directly is Piebald × Spider, which works out every outcome and its odds.