A new mathematical model sheds light on a long unresolved question: that of the origin of piebaldism, an inborn disorder of pigmentation of the hair (in animals), hair or skin (in humans), due to a hitch in the synthesis of melanin that occurs in the embryonic stage.

This condition is at the base of the "bicolor" fur exhibited by cats, horses and some farm animals, but it is also associated, in humans, with serious hereditary diseases. This is why the research, published in Nature Communication, is particularly important and not only for an aesthetic question.

Common origin. Piebaldism is part of a series of diseases known as neurocristopathies, which originate from the same family of embryonic cells, the neural crest. The condition of the hair, this was known, derives from a mutation of a gene called KIT, but as the pattern of white hair, lacking melanin, spread on the animal's body had not yet been understood.

Previous hypotheses. One of the most widespread theories to date was that the defective gene slowed down the migration of pigmented cells, which develop at the back of the animal and migrate towards the front of the body during embryo development. If the cells migrate too slowly, it was thought, they cannot reach their stomachs and forehead in time: this is why it is often these areas of the hair that present white spots.

Image Two-colored stallion. | Carol Walker / Nature Picture Library / contrast

Too few. Christian Yates, mathematician biologist at the University of Bath (Great Britain), traced the path of melanocytes in mouse embryos affected by KIT gene mutation. And he observed two things: the first is that the pigmented cells do not move more slowly. Indeed, they move faster, but as they move they do not multiply as they should, leaving large areas of hair free of pigmentation.

Random. The second is that, given the same genetic mutation, the behavior of the cells is completely unpredictable and random. Which would explain why in some animals the absence of pigmentation is more evident, but also and above all because in people with neurocristopathies some cases are more serious than others.

Important for man. Beyond explaining the conformation of the patch pattern of cats and horses, the mathematical model used, which takes into account factors such as the speed of movement and the rate of growth of pigmented cells, can be exploited to improve research on diseases such as Waardenburg syndrome, which involves in addition to pigmentation problems also a form of congenital deafness, or Hirschsprung's disease, a congenital pathology of the intestine, both linked to problems in the development of the neural crest.