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Mucopolysaccharidosis

Last updated Nov. 29, 2018

Mucopolysaccharidosis (MPS) is a rare, genetic metabolic condition that involves an inability of the body to breakdown glycosaminoglycans, which are long chains of sugar molecules.


What are the other Names for this Condition? (Also known as/Synonyms)

  • MPS (Mucopolysaccharidosis)
  • Mucopolysaccharide Storage Disease
  • Mucopolysaccharidosis Syndrome

What is Mucopolysaccharidosis? (Definition/Background Information)

  • Mucopolysaccharidosis (MPS) is a rare, genetic metabolic condition that involves an inability of the body to breakdown glycosaminoglycans, which are long chains of sugar molecules
  • The condition is typically inherited in an autosomal recessive manner, meaning two copies (one from each parent) of the faulty gene are needed to cause signs and symptoms of the disorder
  • The inheritance of the faulty genes prevents the body from producing an enzyme that is responsible for breaking down the sugar molecules. This inability to breakdown these sugars, causes it to buildup in the body, leading to many defects
  • There are many subtypes of MPS and these include:
    • Mucopolysaccharidosis Type I: They are of 2 types and include the severe type and the attenuated type (less common)
    • Mucopolysaccharidosis Type II: This type is more commonly prevalent among Jewish communities and can cause severe abnormalities in the affected children
    • Mucopolysaccharidosis Type III: It is the most common type of Mucopolysaccharidosis. MPS Type III is subdivided into 4 types including type IIIA, type IIIB, type IIIC, and type IIID
    • Mucopolysaccharidosis Type IV: It is of 2 types (types IVA and IVB) based on the different genes that code for different proteins/enzymes
    • Mucopolysaccharidosis Type VI: This type is known to cause spinal cord defects and other bone and joint abnormalities
    • Mucopolysaccharidosis Type VII: Babies with severe MPS Type VII may die in utero or shortly after birth, due to a condition known as hydrops fetalis
    • Mucopolysaccharidosis Type IX: It is an extremely rare disorder that results in the formation of several soft tissue tumors in the joints of the body (such as the knees and ankles)
  • Since Mucopolysaccharidosis is a genetic condition, it is present at birth. But, significant signs and symptoms may be seen a little later as the child grows (between 2-8 years). The signs and symptoms may include abnormal facial features, cloudy corneas, abnormal development of spine, heart valve defects, and short stature in children
  • A healthcare professional can use various diagnostic tools, such as a physical exam, electrocardiogram, analysis of urine, and X-rays of the affected regions, to help diagnose Mucopolysaccharidosis
  • There is no cure for Mucopolysaccharidosis and the treatment provided is symptomatic. These can include enzyme replacement, bone marrow transplant, and other organ specific treatments
  • Prognosis for children with Mucopolysaccharidosis depends upon the severity of the signs and symptoms. Nevertheless, the prognosis is generally poor; it often involves death at a young age. Complications, such as nervous system and heart defects, are generally life-threatening that can lead to fatalities

Who gets Mucopolysaccharidosis? (Age and Sex Distribution)

  • Mucopolysaccharidoses are a rare group of congenital disorders. The incidence of the disorder varies according to the subtype of MPS
  • Some of the signs and symptoms may be observed early by 6 months; although, significant features of the disorder often develop between the ages 2 to 8 years
  • This inherited genetic disorder can affect both males and females belonging to different racial and ethnic backgrounds. However, some MPS types are more prevalent in certain regions of the world or among certain populations

What are the Risk Factors for Mucopolysaccharidosis? (Predisposing Factors)

  • A genetic predisposition due to family history increases the risk for Mucopolysaccharidosis

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one's chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Mucopolysaccharidosis? (Etiology)

  • In general, Mucopolysaccharidosis is inherited in an autosomal recessive manner. It is caused by inheriting faulty genes that prevents the body from producing certain enzymes
  • In almost all cases, the genes responsible for MPS have been identified. The gene and enzyme involved, varies according to the subtype of MPS
  • Depending on the subtype of MPS, the gene and the enzyme it codes for varies:
    • Mucopolysaccharidosis Type I: The gene responsible for MPS I is the IDUA gene, which codes for the enzyme alpha-L iduronidase
    • Mucopolysaccharidosis Type II: The gene responsible for MPS II is the IDS gene, which codes for the enzyme iduronate 2-sulfate
    • Mucopolysaccharidosis Type III: There are 4 subtypes of MPS III (subtypes A, B, C, and D); each subtype is governed by a different gene, which codes for different enzymes
    • Mucopolysaccharidosis Type IV: There are 2 subtypes of MPS III (subtypes A and B); each subtype is governed by a different gene, which codes for different enzymes
    • Mucopolysaccharidosis Type VI: The gene responsible for MPS VI is the ARSB gene, which codes for the enzyme arylsulfatase B
    • Mucopolysaccharidosis Type VII: The gene responsible for MPS VII is the GUSB gene, which codes for the enzyme beta-D-glucuronidase
    • Mucopolysaccharidosis Type IX: The gene responsible for MPS IX is the HYAL1 gene, which codes for the enzyme hyaluronidase
  • The enzyme is responsible for breaking down long chains of sugars, called glycosaminoglycans (GAGs). Due to a lack of production of the enzyme, GAG sugar molecules get abnormally accumulated in a structure called lysosome within the cells. The disorder is a kind of “lysosomal storage disease”, because the accumulation within special compartments of the cells, called lysosomes
  • Lysosomes are a kind of recycling plant within the cells - they breakdown larger, more complex organic molecules into smaller molecules, which the cells can then reuse. When important enzymes are not functioning efficiently, the lysosomes become bloated and eventually, the cell gets ‘filled-up’ being unable to function anymore, leading to a disease state
  • The complex molecules glycosaminoglycans used to be called “mucopolysaccharides”; the term “mucopolysaccharidosis” literally means an overabundance of mucopolysaccharides

Autosomal recessive: Autosomal recessive conditions are traits or disorders that occur when two copies of an abnormal gene have been inherited on a non-sex chromosome. If both parents have an autosomal recessive condition, there is a 100% likelihood of passing on the mutated genes to their children. If, however, only one mutant copy of the gene is inherited, the individual will be a carrier of the condition, but will not be present with any symptoms. Children, born to two carriers, have a 25% chance of being homozygous dominant (unaffected), a 50% chance of being heterozygous (carrier), and a 25% chance of being homozygous recessive (affected). 

What are the Signs and Symptoms of Mucopolysaccharidosis?

Mucopolysaccharidosis is a congenital disorder; noticeable features of the disorder are seen when the baby is around 6 months old. In most cases, the onset of significant signs and symptoms occur when the child is between 2-8 years old. Children with severe MPS have an earlier onset of signs and symptoms compared to those with milder conditions.

The commonly observed signs and symptoms of Mucopolysaccharidosis may include:

  • Thick, coarse facial features; enlarged skull
  • Presence of large tongue (macroglossia)
  • Abnormal development of vocal cords; individuals have deep, hoarse voice
  • Abnormal bone growth in the spine, narrowing of the spine
  • Cloudy cornea
  • Frequent ear infection, hearing difficulties
  • Frequent upper respiratory infections
  • Stunted growth
  • Multiple skeletal deformities; degenerative joints causing joint stiffness
  • Spinal cord defects
  • Sleep disorder such as sleep apnea
  • Decrease in mental cognition
  • Enlarged liver (hepatomegaly) and enlarged spleen (splenomegaly)

The following may be observed with respect to some of the specific subtypes:

  • Mucopolysaccharidosis Type III mainly affects the functioning of the brain and spinal cord and manifests as neurological signs and symptoms
  • Mucopolysaccharidosis Type IV mainly affects the skeletal system of the body including the spine and joints; it does not usually affect the mental and intellectually capacity
  • Mucopolysaccharidosis Type VII can cause an excess buildup of fluid in the fetus, known as hydrops fetalis, which can be fatal for the baby in the womb
  • Mucopolysaccharidosis Type IX is manifested by the presence of numerous soft tissue tumors, mostly forming around the body joints that give rise to movement issues

How is Mucopolysaccharidosis Diagnosed?

Diagnostic tools used by a healthcare provider in the diagnosis of Mucopolysaccharidoses can include:

  • Physical examination and analysis of previous medical history
  • Peripheral smear exam may reveal abnormal lymphocytes containing cytoplasmic inclusions
  • Urine tests: Increased levels of dermatan sulfate and heparin sulfate may be seen
  • Hearing tests
  • Sleep studies may be performed
  • X-ray of different parts of the body may reveal bony abnormalities
  • Electrocardiogram (EKG) to test the heart function
  • Echocardiogram to determine heart defects
  • MRI scan of brain to determine brain defects
  • Genetic testing for changes in specific genes
  • In many cases, the diagnosis is confirmed in the lab by enzyme assays, performed on fibroblast cells or leukocytes

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Mucopolysaccharidosis?

Some of the common complications of Mucopolysaccharidosis may include:

  • Inguinal hernia causing a bulge on the side of the pubic bone, abdominal weakness, numbness in the groin, groin pain especially while coughing or lifting heavy objects
  • Umbilical hernia causing an usually painless, soft bulge at the navel; the bulge is more visible when the baby cries or coughs
  • Deafness
  • Short stature
  • Frequent incidence of pneumonia
  • Heart valve defects; congestive heart failure
  • Nervous system defects including fluid buildup in the brain (hydrocephalus)
  • Decrease in mobility due to bone and joint defects
  • Carpal tunnel syndrome causing hand signs and symptoms such as radiating pain within the hand, tingling sensation and numbness, weakness in strength of hand muscles, etc.
  • Decreased life span

The complications may vary depending upon the specific subtype of MPS.

  • Communication difficulties, vision and hearing loss, and seizures are noted in MPS Type III
  • MPS Type IV can result in severely reduced mobility and severely compressed spinal cord leading to paralysis
  • Severe gastrointestinal tract abnormalities and a specific condition called hydrops fetalis that results in stillbirths are noted in MPS Type VII

How is Mucopolysaccharidosis Treated?

There is no cure for Mucopolysaccharidosis, since it is a genetic condition. The treatment for MPS is dependent on individual signs and symptoms and based on the organs that are affected. Since, this congenital condition involves various parts of the body and body systems, a team of healthcare professionals of diverse specialties are needed to manage MPS. An individualized treatment (case-by-case approach) is provided to improve the quality of life. This is also based on the specific set of signs and symptoms and complications that develop in each child/individual.

The treatment measures may include:

  • Enzyme replacement therapy: Replacement of the missing enzyme to help in the breakdown of glycosoaminoglycans
  • Bone marrow transplant, if necessary
  • Other organ specific treatments as specified by the healthcare provider including:
    • Orthopedic surgery for correcting bone and joint abnormalities
    • Hernia repair for inguinal and umbilical hernia
    • Corneal transplant for vision abnormalities
    • Tonsillectomy for frequent ear and throat infections
    • Correction of hearing defects
    • Surgical treatment for carpal tunnel syndrome
  • For improving motor skills and mental disabilities, special therapeutic treatment (by physical and occupational therapists) and supportive care is required
  • Additionally for Mucopolysaccharidosis Type IX: Removal of soft tissue tumors in the joints through complete surgical excision may be undertaken
  • Research is being currently undertaken to treat Mucopolysaccharidosis using gene therapy

Note: Sometimes, enzyme replacement therapy and/or bone marrow transplant may not be an effective treatment option for certain MPS types (such as for type III and IV).

How can Mucopolysaccharidosis be Prevented?

  • Currently, there are no specific methods or guidelines to prevent Mucopolysaccharidoses, since these are genetic condition
  • Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
  • If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
  • Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders such as Mucopolysaccharidosis
  • Regular medical screening at periodic intervals with tests, scans and physical examinations are mandatory

What is the Prognosis of Mucopolysaccharidosis? (Outcomes/Resolutions)

Mucopolysaccharidosis is a progressive disorder that has a generally poor prognosis, with the exception of MPS Type IX. However, the prognosis also depends on the subtype of the disorder and the severity of the signs and symptoms.

  • Mucopolysaccharidosis Type I: The prognosis is poor; many children die within the first 12 months. The average survival period for children who overcome the first year is about 12 years
  • Mucopolysaccharidosis Type II: Children, who survive the initial few years, are severely affected by multiple congenital defects and developmental deformities. Many individuals rarely live beyond the age of 20 years
  • Mucopolysaccharidosis Type III: Children with types IIIB, IIIC, and IIID have a much better prognosis than those with MPS Type IIIA, who typically do not survive beyond the second decade
  • Mucopolysaccharidosis Type IV: Children with milder symptoms are known to reach middle-age with appropriate treatment; while those with severe symptoms may not live beyond adolescence
  • Mucopolysaccharidosis Type VI: Some children with mild presentations are known to reach adulthood, while others with severe disorder may die by late childhood
  • Mucopolysaccharidosis Type VII: Children with mild disorder are known to reach early adulthood; those with severe forms of the condition generally die during infancy or childhood
  • Mucopolysaccharidosis Type IX: It is a less severe form of MPS that does not affect the intellectual ability and joint movement range. The severity of the condition depends upon the signs and symptoms and the response to treatment

In many cases, children are known to develop nervous system and heart valve defects and/or have airway obstruction. These are the major factors that lead to fatalities.

Additional and Relevant Useful Information for Mucopolysaccharidosis:

Please visit our Congenital & Genetic Disorders Health Center for more physician-approved health information:

http://www.dovemed.com/diseases-conditions/congenital-genetic-disorders/

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Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Nov. 7, 2016
Last updated: Nov. 29, 2018

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