Hurler Syndrome (MPS I Disease): What Are the Symptoms and Treatment?

How Molecule Storage Within The Body's Cells Cause MPS I (Hurler's Syndrome)

Baby Girl Getting a Checkup. Credit: Christopher Futcher / Getty Images

There is a group of genetic disorders called mucopolysaccharidoses (MPS) in which critical body enzymes (chemicals) are missing or not enough. MPS I disease is caused by a deficiency in a particular enzyme called alpha-L-iduronidase. 

The enzyme Alpha-L-iduronidase breaks down long chains of sugar molecules so that the body can dispose of them. Without the enzyme, the big molecules of sugar build up and progressively damage parts of the body.

The build up of molecules (glycosaminoglycans or GAGs) happen in the lysosomes (a special cavity in the cells that holds a variety of enzymes). The exact GAGs that build up in the lysosomes are different in each case of MPS disease.

There are 7 sub-types of MPS disease and MPS I is the first subtype (the others are MPS II, MPS III, MPS IV, MPS VI, MPS VII, and MPS IX). Each of the disorders can cause a variety of different symptoms, but many of the diseases share similar symptoms, such as:

  • Corneal clouding (eye problems)
  • Short stature (dwarfism or below typical height)
  • Joint stiffness
  • Speech and hearing problems
  • Hernias
  • Heart problems.

Globally, MPS I occurs in about 1 in every 100,000 births and is divided into 3 groups according to the type, severity, and the way the symptoms progress. It is inherited in an autosomal recessive pattern, meaning that a child must inherit two copies of the gene for MPS I, one from each parent, in order to develop the disease.

 

A Continuous Spectrum of Disease: Ranges of MPS

MPS I is considered to exist on a spectrum from severe to mild (attenuated).

  • Severe form, also known as Hurler syndrome or MPS I H: Children affected with the severe form may have mental retardation, short stature, stiff joints, speech and hearing impairment, heart disease, pain and a shortened life span.
  • Attenuated form, also known as Scheie syndrome or MPS I S: Children born with this form have normal intelligence and may live to adulthood.

Some children may have normal intelligence and mild to severe physical symptoms; this condition may be called Hurler-Scheie syndrome or MPS I H-S.

These symptoms are very similar to those of Hunter syndrome, but Hurler syndrome symptoms become worse much faster than Hunter syndrome type A.

What Exactly Is Hurler Syndrome and How Does It Affect a Child?

Hurler Syndrome or Hurler Disease is the historical term for the most severe version of MPS. Hurler was the last name of the doctor who first described the condition.

A baby will show few signs of the disorder at birth but within a few months (once molecules begin to build up in the cells) symptoms begin. Bone deformities may be detected. The heart and respiratory system are affected, as are other internal organs including the brain. The child grows but remains behind in both physical and mental development for his age.

The child may have trouble crawling and walking, and problems with his joints develop, causing parts of the body like his hands to be unable to straighten out. Children with Hurler syndrome usually succumb to problems such as heart failure or pneumonia.

Diagnosis of Hurler Disease

Diagnosis of Hurler syndrome is based on the child's physical symptoms. Generally, the symptoms of severe MPS I will be present during the first year of life, while the symptoms of attenuated MPS I appear in childhood.

Treatment Options

There is as yet no cure for MPS I, so treatment has focused on relieving symptoms. Aldurazyme (laronidase) replaces the deficient enzyme in MPS I. Aldurazyme is given by intravenous infusion once per week for life to people with MPS I. Aldurazyme helps relieve symptoms but is not a cure.

Another treatment available for MPS I is bone marrow transplant, which puts normal cells in the body that will manufacture the missing enzyme. However, many children with Hurler syndrome have heart disease and are not able to go through the chemotherapy required for the transplant.

Many specialists are involved in the care of an individual with MPS I. A genetic counselor can talk with the family and relatives about the risks of passing on the syndrome.

Source:

MPS I (Hurler, Hurler-Scheie, Scheie syndrome). National MPS Society. Accessed on 2/19/2016

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