Mucopolysaccharidosis I (MPS I) is an inherited Lysosomal Storage Disorder affecting dogs. Affected dogs have insufficient activity of the Enzyme alpha-L-iduronidase, which is responsible for breaking down glycosaminoglycans (GAGs). GAGs are an important component of tissues throughout the body. In affected dogs there is an accumulation of breakdown products in cells causing abnormal growth and function of many different organ systems. Affected dogs typically present after 4 to 6 months of life with initial symptoms of bone and joint disease including joint laxity, delayed growth, skeletal deformities and pain on handling. Clinical signs of MPS I are most commonly associated with accumulations in the heart, bones, joints, nervous system and eyes. Other features of MPS I include cloudy eyes, arched back, stiff gait, umbilical hernia and a characteristic upturned nose. Dogs usually die due to complications of the disease or are humanely euthanized by 2-3 years of age.