Mucopolysaccharidosis type IV (MPS IV), also known as Morquio syndrome, is a rare metabolic condition in which the body is unable to break down long chains of sugar molecules called glycosaminoglycans. As a result, toxic levels of these sugars accumulate in cell structures called lysosomes, leading to the various signs and symptoms associated with the condition. These signs and symptoms may include abnormalities of the skeleton, eyes, heart and respiratory system. There are two forms of MPS IV. MPS IVA is caused by changes in the GALNS gene. MPS IVB is caused by genetic changes in the GLB1 gene. Both forms are inherited in an autosomal recessive manner.