The curse of the 33 spots...
"A change in breeders' attitude and breeding practices is mandatory because neither the permanent elimination of animals not "fitting" a fancy standard nor the continuous production of defective genotypes is legal." - Gerlitz S., Wessel G., Wieberneit D., & Wegner W.
Megacolon is a genetic condition that is caused by the KIT gene. This comes into play when a rabbit inherits two of the dominant versions of the "English spotting gene" (En/En). There are three options possible when inheriting the spotting genes. The latest genetic study, from the University of Bologna in Italy, shows that if a rabbit inherits a recessive and dominant (En/en - normal amount of spots) or two recessive (en/en - solid color, no spots) English spotting genes they will not have megacolon. Only rabbits that inherit two of the dominant versions of the "English spotting gene" (En/En - very lightly spotted rabbit) can be affected by megacolon.
During early cell migration early in the rabbit's embryonic development the KIT gene expresses itself resulting in potential problems. KIT controls some cell processes such as cell division and cell movement (migration). This includes the development of cells in the GI tract and cells called melanocytes (melanin). This results in a large reduction of cells to the rabbit's outer muscle wall in the GI tract (cecum and ascending colon). These pacemaker cells control the rate and strength that the outer muscle wall contracts that help move things along in the affected area. This is also the cause for the reduced number of spots on the rabbit's fur.