Also known as Maroteaux-Lamy disease, and is a type of lysosomal storage disease where large sugar molecules are unable to be broken down by the body as they normally would. In the MPS-VI variant of mucopolysaccharidosis the critical enzyme arylsulphatase B is lacking from the body. This results in the substance dermatan sulphate building up within cells, as it cannot be broken down and excreted. This build up of material within cells interferes with normal cell function as more and more room is taken up by the storage of waste materials. There are a large number of adverse affects throughout the body, with some of the most striking being on development of the skeleton.
MPS-VI results in stunted growth, abnormal bone development resulting in skeletal deformities, especially to the hips and also the spine, forelimbs and sternum. There may also be quite marked facial deformity, which may affect the breathing, and clouding of the corneas. Signs are usually apparent by 3 - 4 months of age. In addition to outward signs there is thickening of the heart valves and the muscle of the body is affected, including heart muscle and the muscle of blood vessels. It is common for the ends of bones (called the epiphyses) to "slip" due to improper formation initially, resulting in joint pain and lameness as dogs get older. However it is uncommon for a dog to survive beyond 3 years of age due to continued accumulation of waste product in cells and continued cell dysfunction and eventual death throughout the body.
Some mucopolysaccharides do leak from cells, and initial diagnostic screening is often carried out by testing urine for the presence of glycosaminoglycans. There are more obvious deformities associated with MPS-VI compared to some of the other types of mucopolysaccharidoses, which should arouse suspicion in breeds that are known to be affected. Genetic testing is also available, and breeding animals should be screened to prevent the breeding of two carrier animals, which risks producing affected offspring.
There is a new treatment which is on the horizon for this particular storage disease, although it remains expensive and somewhat experimental presently. A bone marrow transplant is an option for this disease, as the white blood cells provide a source of the missing arylsulphatase B enzyme that is needed. Generally a normal littermate is used as a donor, and the procedure needs to be carried out in a young pup so that the bones and organs have a chance to develop normally. This is one of the few lysosomal storage diseases where there is a possible treatment option. The alternative is euthanasia when quality of life is no longer acceptable.