A mutant gene that led to a spinal malformation spread throughout the community and became the norm. The spine was literally curtailed, ending (in what is described as a true of rumpy Manx) in a hollow where a tail should have been. Cats with brief stumps of tails were also born, and these are called stumpies, stubbies or risers. The gene that causes this condition is related to the gene that causes spina bifida in humans.
The facts presented in this Blog Post were retrieved from 'The Ultimate encyclopedia of cat breeds and cat care' by Alan Edwards, and also from the Purina website.