Hypoplasia of dens is a congenital non-formation of the pivot point of the second cervical vertebra, which leads to spinal cord

Spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

 damage. Onset of the condition may occur at any age, producing signs ranging from neck pain to quadriplegia. Hypoplasia of dens affects dogs. It is more commonly seen in certain breeds, including the Chihuahua

Chihuahua (dog)

The ' is the smallest breed of dog and is so named for the state of Chihuahua in Mexico. Chihuahuas come in a wide variety of sizes, head shapes, colors and coat lengths.-History:...

, the Papillon

Papillon (dog)

The papillon , also called the Continental Toy Spaniel, is a breed of dog of the Spaniel type. One of the oldest of the toy Spaniels, it derives its name from its characteristic butterfly-like look of the long and fringed hair on the ears. A papillon with dropped ears is called a phalène...

, the Pointer

Pointer (dog breed)

The Pointer, often called the English Pointer, is a breed of dog developed as a gun dog. It is one of several pointing breeds.-Appearance:...

 and the Yorkshire Terrier

Yorkshire Terrier

The Yorkshire Terrier is a small dog breed of terrier type, developed in the 19th century in the county of Yorkshire, England to catch rats in clothing mills. The defining features of the breed are its size, to , and its silky blue and tan coat...

.