Does anyone know the biochemical pathway involved in producing blue fish? Genes regulate entire pathways, so if something is altered in development due to the gene(s) that cause blue, it is possible that it is also what leaves blues susceptible to the disease.
In many mammals, spotting genes have a lot of problems associated with them, especially when homozygous (two pairs of the same version of the gene [called alleles]). Basically, the gene disrupts the migration of precursor cells (undifferentiated neural crest cells) that would normally eventually become a myriad of different cells, including pigment cells. It causes the white spots, but it also leaves other areas not fully developed. In homozygous animals of some species, it can cause problems with hindgut development, deafness, and other problems.
For those that have spawned any of the blues that have succumbed to this disease, determining their genetics might be very helpful in learning more about what makes them susceptible. I really don't know much about betta genetics, so bear with me.
From what I gather, steel blues are the result of two steel blue genes. I am not sure if it is dominant or recessive. Royal blue is one green and one steel blue gene. So the question is, do royal blues get this disease, or just steel blues?