Congenital hypothyroidism with goiter (CHG) is an inherited disease affecting rat terriers. Affected dogs lack an Enzyme that is important in the production of thyroid hormone which is necessary for the normal development and metabolism of dogs. At 3-8 weeks of age, dogs with CHG are generally noted to have reduced movement and to be small when compared to their littermates. Enlarged thyroid glands (goiter) are often noticeable as a swelling on the neck. Affected puppies exhibit dwarfism with short legs, large heads, and fluffy hair coats absent of guard hairs. In addition, affected dogs develop a wide variety of neurological and neuromuscular deficits. The condition progresses to failure to thrive and death. Most symptoms can be prevented or will regress if the condition is diagnosed early and affected dogs are treated with thyroid hormone medication. However, the thyroid glands may continue to enlarge over time despite treatment and can eventually obstruct the dog’s airway.