Mucopolysaccharidosis Type VII
What is mucopolysaccharidosis type VII?
Mucopolysaccharidosis type VII (MPS VII), also called Sly syndrome, is a rare genetic condition that causes health problems in many areas throughout the body. MPS VII is caused due to a deficiency in the enzyme B-glucuronidase The enzyme, beta-glucuronidase, is required for the degradation of the GAGs dermatan sulfate (DS), heparan sulfate (HS), and chondroitin 6 sulfate (CS). When the essential enzyme is deficient, a type of sugar called glycosaminoglycans (GAGs) store in the body and cause the health problems associated with MPS VII. The main health problems in people with MPS VII include bone problems like abnormally shaped back bones (vertebrae) and ribs, enlarged skull, too small and too thick leg bones (hypoplastic epiphyses and thickened diaphyses) and bullet-shaped finger and toe bones (metacarpals). People with MPS VII can also have medical problems such as weakened heart valves that cause artery disease, frequent respiratory infections, frequent ear and sinus infections, hearing loss, breathing difficulties, sleep apnea (when breathing pauses or is very shallow during sleep), diarrhea, constipation, vision loss from glaucoma or cloudy corneas (the clear outer layer of the eye), enlargement of the liver and spleen, and developmental and learning problems.
There is a wide disease spectrum and disease progression. Some individuals with the attenuated form (historically referred to as mild diseases) of MPS VII may have little to no cognitive problems but suffer with skeletal and cardiac problems. Then there are patients that have cognitive impairment and learning difficulties without any physical symptoms.
Dr. Sly first described the syndrome in 1973 and thus far, Sly syndrome is the rarest of all the 11 forms of MPS disease.
Genetic changes, or mutations, in the GUSB gene cause a large sugar molecule called glycosaminoglycans (GAGs) to build up in different parts of the body. GAGs were originally called mucopolysaccharides, which is where this condition gets its name. This buildup of GAGs is what causes health problems for people with MPS VII, which is why it is caused a storage disorder or, more specifically, a lysosomal storage disorder.