Brachycephaly is a skull shape trait seen in a number of breeds and is characterized by a shortened
head, pushed in face, and typically an underbite with widely spaced shallow orbits. Breeds known to
exhibit this trait include Pugs, Boxers, Bulldogs and Boston Terriers. The overall shape and size of a
dog’s skull is likely the result of multiple genetic factors with a mutation in the BMP3 gene being one
factor contributing to a short muzzle. BMP3 is also suspected to be essential for normal craniofacial
development with mutations in this gene likely leading to abnormal craniofacial development. This
mutation is typically fixed or carried in two copies in breeds such as Pug, Pekingese, French Bulldog,
Brussels Griffon and Boston Terriers. Additional mutations such as SMOC2 are currently being studied
to determine their effect on skull development and brachycephaly.

• Boston Terrier
• Brussels Griffon
• Bulldog
• Chihuahua
• French Bulldog
• Jack Russell Terrier
• Japanese Chin
• Miniature Poodle
• Miniature Schnauzer
• Norwich Terrier
• Pekingese
• Pembroke Welsh Corgi
• Pomeranian
• Pug
• Scottish Terrier
• Shih Tzu
• Staffordshire Bull Terrier
• Sussex Spaniel
• Teddy Roosevelt Terrier
• Tosa Inu

A (CLEAR/NORMAL): These dogs have two copies of the normal gene and will likely not have a short
muzzle length nor pass this mutation to their offspring.

B (CARRIER/NOT AFFECTED): These dogs have one copy of the normal gene and one copy of the
mutation associated with this trait. They will likely not have a short muzzle length but will, if bred, pass
the mutation to 50% of its offspring, on average.

C (AT RISK/AFFECTED): These dogs have two copies of the mutation associated with short muzzle length
in some breeds.