Relevant Section on the genetics:

For the study, the researchers took blood from five of the cats, which had been adopted, and conducted a DNA test on four of the felines, which turned up no genetic mutations associated with white fur.

They then performed a whole genome sequencing for two of the cats, and this step turned up a deletion in what's called the KIT gene, which can encode whether white will turn up in a feline's coat (scientists have also connected variations in the KIT gene to piebald patterns in various animals like horses and mice.)

"In summary, comparative data from other species and genotype segregation analysis support the newly discovered KIT region deletion as potentially being a cause of salmiak coat color in cats," the researchers conclude.