Maroteaux-Lamy syndrome (MPS VI)

MPS VI is one of the mucopolysaccharidoses (MPS), a group of lysosomal storage disorders. Lysosomes are the parts of a cell that break down and recycle used material. In MPS VI, the enzyme arylsulfatase B is missing or weak. Long sugar chains called glycosaminoglycans (GAGs), mainly one called dermatan sulfate, cannot be broken down and build up in tissues.

Severity varies. Doctors now describe a range from rapidly progressing to slowly progressing disease, with forms in between. Rapidly progressing forms show clear signs before age 2. Slowly progressing forms can go unrecognized for years. In published reports, people with these forms were diagnosed between ages 9 and 42.

Unlike several other types of MPS, MPS VI usually does not affect intelligence. Its effects are mostly on the body.

MPS VI is caused by changes in both copies of the ARSB gene. This gene carries the instructions for making the arylsulfatase B enzyme.

It is inherited in an autosomal recessive pattern. Each parent usually carries one changed copy and has no symptoms. When both parents are carriers, each child has a 1 in 4 chance of being affected.

It is not caused by anything a parent did, and it cannot be caught from another person. A genetic counselor can explain what test results mean for brothers, sisters and future pregnancies.

Babies usually look healthy at birth, and signs often start in early childhood. Growth slows, and many children have short stature. Joints become stiff and bent (contractures), and x-rays show a pattern of bone changes called dysostosis multiplex. The face may slowly look coarser, and the tongue may be large.

Heart valve changes are found in everyone with MPS VI. Narrow airways lead to frequent ear, nose and throat infections and to pauses in breathing during sleep (sleep apnea). The clear front of the eye (the cornea) often turns cloudy, which can cause serious vision loss, and hearing loss is common. The liver and spleen can grow larger, and hernias are common.

Pressure on nerves in the wrist can cause carpal tunnel syndrome, with numbness and weakness in the hands. A narrow spinal canal in the neck (spinal stenosis) can press on the spinal cord. Some people develop a buildup of fluid in the brain (hydrocephalus).

Doctors often first suspect MPS VI in a young child with slowing growth, stiff joints, hernias, frequent ear infections or bone changes on x-ray. In slowly progressing forms, the first signs are often joint stiffness and pain. These start at an average age of about 10, and sometimes not until adulthood, so the diagnosis can be missed for years.

A urine test usually comes first. It shows raised GAGs, especially dermatan sulfate. This raises suspicion but does not confirm the diagnosis. The key test measures arylsulfatase B activity in white blood cells or skin cells (fibroblasts). The lab also checks other sulfatase enzymes, to rule out a different condition called multiple sulfatase deficiency.

The diagnosis is confirmed by arylsulfatase B activity below 10% of the lowest normal level, by finding changes in both copies of the ARSB gene, or by both. MPS VI is not on the U.S. recommended newborn screening panel. Taiwan screens newborns for it, and a pilot study in Washington State tested more than 100,000 newborns. Once a family's gene changes are known, brothers and sisters can be tested.

Galsulfase (Naglazyme) is an enzyme replacement therapy that supplies the missing enzyme. It is given by vein once a week, as an infusion lasting at least four hours, for as long as treatment continues. The FDA approved it in 2005, and the European Union approved it in 2006. Its main trial included 39 people aged 5 to 29. After 24 weeks, the distance they walked in 12 minutes rose by 109 meters on average, compared with 18 meters on placebo.

Galsulfase carries a boxed warning for severe allergic reactions, including anaphylaxis, so infusions start where staff can treat them. International guidance from 2019 recommends starting it as soon as possible after diagnosis. Studies suggest that starting early helps growth more. Its effect on the bones and the cloudy cornea has been limited.

Much of care treats problems as they appear. That can include breathing support at night, a cornea transplant for serious vision loss, and surgery for carpal tunnel or the spine. Regular heart, lung, eye, hearing and spine checks help the team act early. Anesthesia carries extra risk because of narrow airways, so operations are planned by teams experienced with MPS, in hospitals with intensive care.

A donor stem cell transplant gives the body a lasting source of the enzyme. In MPS VI it is not standard care, unlike in severe MPS I (Hurler syndrome). The 2019 guidance says its balance of benefit and risk is less clear than in other types of MPS. European transplant guidelines from 2026 list it as an option mainly when enzyme therapy has failed or is not possible. Some centers, such as one in Turkey that reported on 17 children in 2025, offer it as a one-time alternative to lifelong infusions.

Families often juggle many specialists: genetics, heart, lungs, ear, nose and throat, eyes, bones and the spine. International guidance recommends regular checks at every stage, including a yearly MRI of the spine in children and a yearly walking test.

Weekly infusions take several hours, often at a hospital or infusion center, though home infusion is possible in some regions. Guidance suggests considering a port, a small device placed under the skin, to make frequent infusions easier. Operations are common, and each anesthetic needs careful planning.

Because MPS VI does not affect intelligence, the hardest parts are mostly physical. Patient groups told the 2019 guideline authors that the biggest challenges were endurance, use of the hands, hearing, vision and breathing.

Most people with MPS VI are treated with enzyme therapy, not a transplant. When a specialist team does consider a transplant, the cells come from another person. European transplant recommendations from 2025 rate it a clinical option for children, used after a careful look at risks and benefits. That applies whether the donor is a matched brother or sister, a matched unrelated volunteer or a less closely matched donor.

The 2019 guidance says a matched relative, preferably not a carrier, or a well-matched adult unrelated donor may be an option. Published cases have used brothers and sisters, other relatives, unrelated volunteers and cord blood. In a Turkish series of 17 children transplanted between 2020 and 2023, 13 had a matched unrelated donor. All 17 were alive and making normal enzyme levels after a median of 14 months.

A shortage of registry donors is not the main barrier for this condition, because most people are treated with enzyme therapy. Joining a registry still helps the many other patients who need an unrelated donor.

Outlook depends mostly on how fast the disease moves. MedlinePlus Genetics says that, without treatment, people with severe disease may survive only until late childhood or adolescence. People with milder forms usually live into adulthood, though their lives may be shorter. Heart disease and blocked airways are the main causes of death.

Enzyme therapy has changed the picture. A 2021 review describes a survey of 121 people treated for an average of 7 years. It found better lung function and endurance, steadier heart function and longer survival. Another study linked starting before age 5 with better growth, fewer serious breathing problems and lower death rates.

Transplant has become safer across the MPS group, but serious risks, including death, remain. In the largest registry study, of transplants done between 1982 and 2007, about two in three people were alive one and three years later. In a recent series from Turkey, all 17 children were alive after a short follow-up.