The King Charles Spaniel (also known as the English Toy Spaniel) is a small dog breed of the spaniel type. In 1903, the Kennel Club combined four separate toy spaniel breeds under this single title. The other varieties merged into this breed were the Blenheim, Ruby and Prince Charles Spaniels, each of which contributed one of the four colours available in the breed. A natural bobtail can be found in some members of the breed, which is not a mutation of the T-box gene, and so is allowed under conformation show rules. Health-related research on the breed has been limited, with no major studies conducted in Britain. However, it has been included in studies outside the UK, including by the Orthopedic Foundation for Animals (OFA) in the United States. This condition may cause neurological symptoms that require the dog to be euthanised.