MPS

Mucopolysaccharidosis (MPS) is a group of metabolic disorders caused by the absence or malfunctioning of lysosomal enzymes needed to break down molecules called glycosaminoglycans (GAGs). These molecules, previously known as mucopolysaccharides, are long chains of sugar molecules used in the building of connective tissues in the body. The inability to break down GAGs leads to their accumulation in cells, blood, and connective tissues, resulting in progressive cellular damage which affects appearance, physical abilities, organ and system functioning, and, in most cases, mental development.

Types

Mucopolysaccharidosis is categorized into several types, each associated with a specific enzyme deficiency and spectrum of symptoms. These include:

• MPS I (Hurler, Hurler-Scheie, Scheie syndromes) - caused by a deficiency in the enzyme alpha-L-iduronidase.
• MPS II (Hunter syndrome) - caused by a deficiency in the enzyme iduronate-2-sulfatase.
• MPS III (Sanfilippo syndrome) - has four subtypes (A, B, C, D), each caused by a deficiency in a different enzyme involved in the degradation of heparan sulfate.
• MPS IV (Morquio syndrome) - has two subtypes (A and B), caused by deficiencies in enzymes needed to break down keratan sulfate.
• MPS VI (Maroteaux-Lamy syndrome) - caused by a deficiency in the enzyme arylsulfatase B.
• MPS VII (Sly syndrome) - caused by a deficiency in the enzyme beta-glucuronidase.
• MPS IX (Natowicz syndrome) - a very rare form, caused by a deficiency in the enzyme hyaluronidase.

Symptoms

The symptoms of MPS vary widely among individuals and types but generally include physical abnormalities, organ and system dysfunction, and, in some cases, neurological decline. Common symptoms across the MPS types can include coarse facial features, clouded corneas, joint stiffness, short stature, and heart valve abnormalities.

Diagnosis

Diagnosis of MPS involves a combination of clinical examination, family history, and laboratory tests measuring enzyme activity in blood, urine, or tissue samples. Genetic testing can confirm the diagnosis and identify the specific type of MPS.

Treatment

Treatment options for MPS are limited and focus on managing symptoms and improving quality of life. Enzyme replacement therapy (ERT) is available for some types of MPS and has shown to improve certain physical symptoms and quality of life. Hematopoietic stem cell transplantation (HSCT) has also been used in some cases, particularly for MPS I, with varying degrees of success. Gene therapy is a promising area of research and could offer more definitive treatments in the future.

Prognosis

The prognosis for individuals with MPS varies depending on the type and severity of the condition. Some individuals may have a normal lifespan with mild symptoms, while others may experience severe complications and a shortened lifespan.