Cysts on a cat's sweat gland, congential hypotrichosis, a condition in which a cat is born at birth with very little or even no hair, or Cushing's disease may also be factors. (second-opinion-doc.com)
See Congenital hypotrichosis, Color dilution / mutant alopecia, Black hair folliclular dystrophy / alopecia, Follicular dysplasia (non-color linked) (lowchensaustralia.com)