Chihuahuas, and other toy breeds, are also prone to the sometimes painful condition known as patella luxation.
Skull abnormalities
Another genetic abnormality in Chihuahuas and toy breeds is hydrocephalus, or water on the brain. This condition surfaces in young puppies and often results in the death of a puppy by the time that it reaches six months of age. It is thought that this disease is often diagnosed by the pup having an abnormally large head during the first several months of life, but other symptoms are more noticeable (since "a large head" is such a broad description). Chihuahua puppies exhibiting hydrocephalus usually have patchy skull platelets rather than a solid bone, and typically are lethargic and do not grow at the same pace as their siblings. A true case of Hydrocephalus can be diagnosed by a veterinarian, though the prognosis is grim.Chihuahuas are also known for their moleras, a soft spot in their skulls.
Chihuahuas are the only breed of dog to be born with an incomplete skull. The molera does fill in with age, but great care needs to be taken during the first six months until the skull is fully formed. Many veterinarians are not familiar with Chihuahuas as a breed, and mistakenly confuse a molera with hydrocephalus. The Chihuahua Club of America has issued a statement regarding this often deadly misdiagnosis.
Chihuahuas are also prone to eye infections due to their large, round, protruding eyes and their relatively low ground clearance.
