Mucopolysaccharidosis type VII

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

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," 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 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.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the GUSB gene cause MPS VII. This gene provides instructions for producing the beta-glucuronidase (β-glucuronidase) enzyme, which is involved in the breakdown of large sugar molecules called glycosaminoglycans (GAGs). GAGs were originally called mucopolysaccharides, which is where this condition gets its name. Mutations in the GUSB gene reduce or completely eliminate the function of β-glucuronidase. The shortage (deficiency) of β-glucuronidase leads to the accumulation of GAGs within cells, specifically inside the lysosomes. Lysosomes are compartments in the cell that digest and recycle different types of molecules. Conditions such as MPS VII that cause molecules to build up inside the lysosomes are called lysosomal storage disorders. The accumulation of GAGs increases the size of the lysosomes, which is why many tissues and organs are enlarged in this disorder. Researchers believe that the GAGs may also interfere with the functions of other proteins inside the lysosomes and disrupt many normal functions of cells.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of the pleura · Very frequent (99-80%)

An abnormality of the pulmonary pleura, the thin, transparent membrane which covers the lungs and lines the inside of the chest walls.

Anterior beaking of lower thoracic vertebrae · Very frequent (99-80%)

Anterior tongue-like protrusions of the lower thoracic vertebral bodies.

Anterior beaking of lumbar vertebrae · Very frequent (99-80%)

Anterior tongue-like protrusions of the vertebral bodies of the lumbar spine.

Ascites · Very frequent (99-80%)

Accumulation of fluid in the peritoneal cavity (between the layers of the peritoneum that lines the abdomen).

Coarse facial features · Very frequent (99-80%)

Absence of fine and sharp appearance of brows, nose, lips, mouth, and chin, usually because of rounded and heavy features or thickened skin with or without thickening of subcutaneous and bony tissues.

Corneal opacity · Very frequent (99-80%)

A reduction of corneal clarity.

Diaphyseal thickening · Very frequent (99-80%)

Tubulation refers to the size and shape of tubular bones. In children and adolescents, the modeling process regulates normal bone growth. Final shaft (tube) diameter depends on appositional bone growth and the equilibrium between periosteal and endosteal bone resorption and formation. Undertubulation refers to a broad, widened form of the shafts (diaphyses) of long bones.

Flat face · Very frequent (99-80%)

Absence of concavity or convexity of the face when viewed in profile.

Other findings in the same source

From: Orphanet

Additional reported features include Inguinal hernia (Very frequent (99-80%)); Intellectual disability (Very frequent (99-80%)); Lymphedema (Very frequent (99-80%)); Recurrent respiratory infections (Very frequent (99-80%)); Scoliosis (Very frequent (99-80%)); Umbilical hernia (Very frequent (99-80%)); Abnormality of the hip bone (Frequent (79-30%)); Epiphyseal stippling (Frequent (79-30%)); Hepatitis (Frequent (79-30%)); Hydrops fetalis (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Mucopolysaccharidosis type VII is Metabolic Medicine, with a metabolic specialist / clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with metabolic specialist / clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Is a biochemical or molecular result needed to clarify the diagnosis?
• Does this condition require an individual plan for illness or reduced food intake?
• Should nutrition advice come from a specialist metabolic dietitian?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Mucopolysaccharidosis type VII. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.