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Mucopolysaccharidosis type VII
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Mucopolysaccharidosis Type VII (Sly Syndrome)

Mucopolysaccharidosis type VII (MPS VII), also known as Sly syndrome, is a progressive condition with widely variable severity that affects most tissues and organs due to the accumulation of large sugar molecules.

Overview

Mucopolysaccharidosis type VII (MPS VII), also known as Sly syndrome, is a progressive condition that affects most tissues and organs. The severity of MPS VII varies widely among affected individuals.

The most severe cases of MPS VII are characterized by hydrops fetalis, a condition in which excess fluid builds up in the body before birth. Most babies with hydrops fetalis are stillborn or die soon after birth. Other people with MPS VII typically begin to show signs and symptoms of the condition during early childhood. The features of MPS VII include a large head (macrocephaly), a buildup of fluid in the brain (hydrocephalus), distinctive-looking facial features that are described as "coarse facial features," and a large tongue (macroglossia). Affected individuals also frequently develop an enlarged liver and spleen (hepatosplenomegaly), heart valve abnormalities, and a soft out-pouching around the belly-button (umbilical hernia) or lower abdomen (inguinal hernia). The airway may become narrow in some people with MPS VII, leading to frequent upper respiratory infections and short pauses in breathing during sleep (sleep apnea). The clear covering of the eye (cornea) becomes cloudy, which can cause significant vision loss. People with MPS VII may also have recurrent ear infections and hearing loss. Affected individuals may have developmental delay and progressive intellectual disability, although intelligence is unaffected in some people with this condition.

MPS VII causes various skeletal abnormalities that become more pronounced with age, including short stature and joint deformities (contractures) that affect mobility. Individuals with this condition may also have dysostosis multiplex, which refers to multiple skeletal abnormalities seen on x-ray. Carpal tunnel syndrome develops in many children with MPS VII and is characterized by numbness, tingling, and weakness in the hands and fingers. People with MPS VII may develop a narrowing of the spinal canal (spinal canal stenosis) in the neck, which can compress and damage the spinal cord.

The life expectancy of individuals with MPS VII depends on the severity of symptoms. Some affected individuals do not survive infancy, while others may live into adolescence or adulthood. Heart disease and airway obstruction are major causes of death in people with MPS VII.

The exact incidence of MPS VII is unknown, although it is estimated to occur in 1 in 250,000 newborns. It is one of the rarest types of mucopolysaccharidosis.

Causes & Risk Factors

Mutations in the GUSB gene cause MPS VII. This gene provides instructions for producing the beta-glucuronidase (β-

Frequently Asked Questions

irway assessment should begin with polysomnography to quantify apnea‑hypopnea index. If moderate‑to‑severe obstruction is confirmed, options include continuous positive airway pressure (CPAP) at night, surgical interventions such as adenotonsillectomy or supraglottoplasty, and, in advanced cases, tracheostomy. Close collaboration with a pediatric otolaryngologist and pulmonologist is essential, and regular re‑evaluation is needed because airway narrowing can progress as glycosaminoglycans accumulate.
MPS VII is highly variable. Children with the severe hydrops‑fetalis form often do not survive infancy, whereas those with milder phenotypes can live into adulthood with multidisciplinary support. Long‑term care includes annual cardiac echocardiograms, liver imaging, neurodevelopmental assessments, orthopedic monitoring, and vision/hearing evaluations. Early involvement of a metabolic specialist, cardiologist, orthopedist, and developmental therapist improves quality of life and can extend survival into the 30s–40s in the milder spectrum.
definitive diagnosis is made by sequencing the GUSB gene, which encodes β‑glucuronidase. Testing is usually ordered when a child shows a combination of coarse facial features, hepatosplenomegaly, and developmental delay, or earlier if prenatal ultrasound shows hydrops fetalis. Enzyme activity assays on leukocytes or fibroblasts can be done first to flag the disorder, but molecular confirmation is required for counseling and eligibility for enzyme‑replacement therapy (ERT).
The only FDA‑approved disease‑modifying therapy for MPS VII is a recombinant β‑glucuronidase enzyme replacement (vestronidase alfa). Clinical trials show the greatest benefit when treatment begins before irreversible organ damage—ideally in early childhood after diagnosis is confirmed. Hematopoietic stem cell transplantation (HSCT) has been attempted in a few severe cases, but risks are high and it is not standard care. Regular infusions (every two weeks) can improve joint range of motion, reduce liver size, and stabilize pulmonary function, though they do not reverse existing skeletal deformities.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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