MPS VI, Maroteaux-Lamy Disease
What else is it called?
- Arylsulfatase B deficiency
- Maroteaux-Lamy Syndrome
- MPS VI
- Mucopolysaccharidosis 6
- Mucopolysaccharidosis VI
- Polydystrophic Dwarfism
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What causes it?
MPS VI is caused by mutations (changes) in the ARSB gene. This gene provides instructions for producing an enzyme called arylsulfatase B which is responsible for the breakdown of large sugar molecules called glycosaminoglycans (GAGs), originally known as mucopolysaccharides.
Mutations in this gene reduce or eliminate the function of arylsulfatase B. The lack of arylsulfatase B activity causes a build-up of GAGs within the cells, specifically the lysosomes. Lysosomes are sections in the cell that digest and recycle different types of molecules. The build-up of GAGs within lysosomes increases the size of the cells, enlarging many tissues and organs.
How common is it?
The exact prevalence of MPS VI is unknown. It is estimated to affect 1 in 250,000 to 600,000 new-borns.
What are the signs and symptoms?
Individuals with MPS VI are usually diagnosed between 1 to 5 years of age. However, in patients with the more slowly progressing disease, it can be difficult to identify the condition, or they can be misdiagnosed with another condition. MPS VI progresses over time and depending on how severe the enzyme deficiency is, individuals may experience severe disabilities and possibly early death.
Symptoms associated with this condition include:
- Short stature (height significantly below average)
- Macrocephaly (large head)
- Progressively coarse facial features
- Compressed spinal cord
- Carpal tunnel syndrome (causes pain, numbness and tingling in the hand and arm)
- Corneal clouding (cornea appears white or clouded over)
- Impaired vision
- Recurrent otitis media (infection of the middle ear causing inflammation and a build-up of fluid behind the eardrum)
- Impaired hearing
- Recurrent sinopulmonary infections (affecting the sinuses and the airway of the lungs)
- Upper airway obstruction
- Sleep apnoea (when your breathing stops and starts while you sleep)
- Reduced pulmonary (respiratory/lung) function
- Cardiac (heart) abnormalities
- Hepatosplenomegaly (enlarged liver and spleen)
- Umbilical hernias
- Inguinal (groin) hernias
- Reduced joint range of motion
- Dysostosis multiplex (bone deformities)
- Malaise (general feel of discomfort)
- Reduced endurance
How is it diagnosed?
A diagnosis of this condition is based on identifying characteristic symptoms, a full patient and family history, a clinical evaluation and a series of specialized tests.
Specialized urine tests will be done to assess the levels of mucopolysaccharides in the urine. Specialized blood tests will also be carried out to measure the enzyme activity of arylsulfatase B.
Molecular genetic testing will confirm a diagnosis of MPS VI, detecting mutations in the ARSB gene.
Can it be treated?
Previously, treatment for MPS VI was entirely symptomatic and supportive. However, since 2006 Naglazyme (brand name) has been licensed in the EU and UK for enzyme replacement therapy (galsulfase enzyme). Patients with MPS can use enzyme replacement therapy as a long-term therapy where the missing or deficient enzyme (galsulfase) is given through an intravenous infusion. This treatment has resulted in overall less physical deterioration, reduced disability, reduced joint stiffness and improving respiratory function.
Do my family need to be tested?
MPS VI is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of MPS VI is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with MPS VI are carriers.
When both parents are carriers, the risk to the baby in each pregnancy is
- 25% chance (1 in 4) of developing the condition
- 50% chance (1 in 2) for the baby to be a carrier of the condition
- 25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier
Genetic counselling can be requested to get a full explanation.