Mucopolysaccharidosis Type IV

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

• Morquio Syndrome
• MPS4
• Mucopolysaccharide Storage Disease Type IV

What is Mucopolysaccharidosis Type IV? (Definition/Background Information)

• Mucopolysaccharidosis Type IV (MPS IV or Morquio Syndrome) 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 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 (known as the arylsulfatase B enzyme) that is responsible for breaking down the sugar molecules. This inability to breakdown these sugars, causes it to buildup leading to many defects
• Since the condition is genetic, it is present at birth. Although, significant signs and symptoms of Mucopolysaccharidosis Type IV are mostly seen during childhood and involve the skeletal system (leading to significant bone and joint abnormalities)
• A healthcare professional can use various diagnostic tools, such as a physical exam, electrocardiogram, urinalysis (analysis of urine), and X-rays of the affected regions, to help diagnose Mucopolysaccharidosis Type IV
• There is no cure for Mucopolysaccharidosis Type IV; however, the treatment provided is symptomatic. These can include enzyme replacement and corrective surgeries for bone and joint defects. However, bone marrow transplant is not reported to be very effective
• The prognosis of Mucopolysaccharidosis Type IV depends upon the severity of the condition. Children with milder signs and symptoms have a better prognosis than those with severe MPS Type IV

Mucopolysaccharidosis Type IV is subdivided into the following subtypes based on the different genes that are mutated:

• Mucopolysaccharidosis Type IVA (or MPS IV Type A)
• Mucopolysaccharidosis Type IVB (or MPS IV Type B)

Who gets Mucopolysaccharidosis Type IV? (Age and Sex Distribution)

• Mucopolysaccharidosis Type IV is a rare congenital disorder that is present at birth. However, the signs and symptoms are not usually observed at birth, but during early childhood
• The incidence of the condition is between 1 in 200,000 to 1 in 300,000 newborns
• This inherited genetic disorder can affect males and females of different races and ethnic backgrounds

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

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

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 Type IV? (Etiology)

• Mucopolysaccharidosis Type IV is caused by inheriting faulty genes that prevents the body from producing certain enzymes. The condition is inherited in an autosomal recessive manner
• Depending on the subtype of MPS Type IV, the gene and the enzyme it codes for varies:
  • Mucopolysaccharidosis Type IVA: The gene responsible for MPS IVA is the GALNS gene, which codes for the enzyme N-acetylgalactosamine-6-sulfate sulfatase
  • Mucopolysaccharidosis Type IVB: The gene responsible for MPS IVB is the GLB1 gene, which codes for the enzyme beta-D-galactosidase
• The enzyme is responsible for breaking down long chains of sugars, called glycosaminoglycans (GAGs). Due to a lack of production of this 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 break down 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. Mucopolysaccharidosis Type 4 is also known as Morquio Syndrome

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 Aigns and Symptoms of Mucopolysaccharidosis Type IV?

Mucopolysaccharidosis Type IV is a congenital disorder; however, noticeable features of the disorder are not commonly present at birth. The onset of significant signs and symptoms occur during early childhood (by age 2 years). The severity of the condition varies from one child to another and it may be mild or severe. The severity also depends upon the subtype of MPS Type IV.

The signs and symptoms of Mucopolysaccharidosis Type IV are generally the same for both subtypes and may include:

• The skeletal system of the body is typically and significantly affected, which leads to:
  • Bony abnormalities that affect the chest and ribs (including pectus carinatum)
  • Curvature of the spine (scoliosis and kyphosis)
  • Abnormalities in the long bones of the body (arms and legs)
  • Hypermobility (high flexibility) of the joints, especially of the hips and knees (including knock-knees)
  • Difficulty in walking, movement
  • Stunted growth: The body stops growing after it reaches a height of 1-1.5 m (about 5 feet)
  • Narrowing or compression of the spinal cord; due to misaligned vertebral bones (in the neck region)
• Abnormally large head (macrocephaly) with abnormal facial features
• Presence of large tongue (macroglossia)
• Mild enlargement of liver (hepatomegaly)
• Frequent respiratory infections
• Frequent ear infection, hearing difficulties
• Sleep disorder such as sleep apnea
• Corneal clouding
• Heart valve defects

Generally, there is no decrease in mental cognition and the condition does not affect one’s IQ levels.

How is Mucopolysaccharidosis Type IV Diagnosed?

Diagnostic tools used by a healthcare provider in the diagnosis of Mucopolysaccharidosis Type IV 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
• Genetic testing for changes in specific genes
• In many cases, the diagnosis is confirmed in the lab by conducting enzyme-based tests, which are 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 Type IV?

Complications of Mucopolysaccharidosis Type IV 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
• Vision and hearing loss
• Short stature
• Frequent incidence of pneumonia
• Heart defects; congestive heart failure
• Severely reduced mobility due to bone and joint defects
• Severely compressed spinal cord can lead to paralysis
• Decreased life span

How is Mucopolysaccharidosis Type IV Treated?

There is no cure for Mucopolysaccharidosis Type IV, since it is a genetic condition. Treatment for MPS Type IV 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 IV. 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
• Other organ specific treatments as specified by the healthcare provider including:
  • Orthopedic surgery for correcting bone and joint abnormalities
  • Surgical correction for spinal cord and vertebral defects
  • Hernia repair for inguinal and umbilical hernia
  • Corneal transplant for vision abnormalities
  • Tonsillectomy for frequent ear and throat infections
  • Correction of hearing defects
• For improving motor skills, special therapeutic treatment (by physical and occupational therapists) and supportive care is required
• Bone marrow transplant: Presently, this is not found to be a very effective treatment option
• Research is being currently undertaken to treat Mucopolysaccharidosis Type IV using gene therapy

How can Mucopolysaccharidosis Type IV be Prevented?

• Currently, there are no specific methods or guidelines to prevent Mucopolysaccharidosis Type IV, since it is a 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 Type IV
• Regular medical screening at periodic intervals with tests, scans and physical examinations are mandatory

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

Mucopolysaccharidosis Type IV (Morquio Syndrome) is a progressive disorder that has a generally poor prognosis. However, the prognosis also depends upon the severity of the signs and symptoms.

• Children with severe signs and symptoms generally die during late childhood or into adolescence
• Children with milder signs and symptoms are known to reach adulthood (around age 50 years), with adequate support and therapy

Additional and Relevant Useful Information for Mucopolysaccharidosis Type IV:

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

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