VIENNA (AFP) - The white coat of the Lipizzan horses performing at Vienna's prestigious Spanish riding school is caused by a mutated gene, a new study showed, solving a decades-old mystery over the horses' colour.

White and grey horses, including Lipizzans, are born with a darker coat but lose their colour between the age of six and eight due to chromosome mutations, Austrian and Swedish researchers found in the study published Sunday in the scientific journal Nature Genetics.

These genetic changes cause pigment-producing melanocyte cells to be produced more rapidly in these horses so that the stock is quickly used up and the horses lose their pigmentation, according to one of the study's co-authors, Monika Seltenhammer of Vienna's University of Veterinary Medicine.

The study also found that the same chromosome was responsible for the horses' heightened risk of melanoma, a serious skin cancer.

Between 70 and 80 percent of grey and white horses aged 15 or older develop skin disease, said Leif Andersson of the department of medical biochemistry and microbiology at Sweden's Uppsala University.

But the horses are hardly at risk, as the disease cells do not spread as quickly as in humans, said Seltenhammer.

LIKE IT?  LET OTHERS KNOW