It all comes down to irresponsible breeding.
Two Great Dane sisters, Cleo and Skye, were born deaf and blind because an irresponsible back-yard breeder produced a litter by breeding two dogs with the color pattern known as harlequin. It's well known in Great Dane circles that doing this can result in a genetic defect called the double-merle gene.
Puppies with the double-merle gene are predominately white and have a higher chance of being born deaf and with eye defects.
Cleo and Skye were luckier than most double-merle puppies: unlike many, they were given the chance to live. A family adopted them, but after a year they realized they weren't prepared to care for two Great Danes, and they surrendered them to a rescue.
That first rescue couldn't find the sisters foster homes, so for two years they lived in a kennel.
Two moves later, they ended up with Big Dogs Huge Paws, a rescue that specializes in big dogs. They're now three years old, and last weekend Cleo found a home with a family in St. Louis -- but Skye is still waiting for a family.
Despite her disabilities, she's still a happy, affectionate dog.
You can find out more about the two sisters here.