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Mucopolysaccharidosis (MPS) Type I

26 July 2011

Synonyms of Mucopolysaccharidosis (MPS) Type I
• Gargoylism
• Hurler Syndrome (MPS IH)
• Scheie Syndrome (MPS IS)
• Hurler-Scheie Syndrome (MPS IH/S)

General Info

MPS are a group of metabolic disorders caused by the absence or malfunctioning of lysosomal enzymes needed to break down molecules called glycosaminoglycans (GAGs) - long chains of sugar carbohydrates in each of our cells that help build bone, cartilage, tendons, corneas, skin and connective tissue. Glycosaminoglycans (formerly called mucopolysaccharides) are also found in the fluid that lubricates our joints.

The mucopolysaccharidoses are part of the lysosomal storage disease family, a group of about 50 genetic disorders that result when a specific organelle in our body's cells – the lysosome – malfunctions. The lysosome is commonly referred to as the cell’s recycling center because it processes unwanted material into substances that the cell can utilize. Lysosomes break down this unwanted matter via enzymes, highly specialized proteins essential for survival. Lysosomal disorders like mucopolysaccharidosis are triggered when a particular enzyme exists in too small an amount or is missing altogether.

Common Symptoms

Stiffened joints/ Claw hands
Hands and fingers are stiff and uncomfortable, making it difficult for affected individuals to release their hands and fingers from this curved, bowed, and bent fingers position.
Mass in belly (abdomen)
The belly (abdomen) may have a large mass due to a big liver or spleen. This enlarged liver or spleen can cause the belly to appear big, swollen, or distended. It may therefore look like a patient has a big, round belly. A doctor might refer to these symptoms as hepatomegaly and splenomegaly.
Breathing problems
Some patients with MPS have breathing problems, such as noisy breathing, wheezing, shortness of breath, chest pain, and chest tightness.
Abnormal Mongolian Spots (the blue or purple spot birthmark that sometimes looks like a bruise)
Anyone whose Mongolian spots did not completely disappear until after the age of 8 or later should be considered to have had abnormal Mongolian Spots.
Cloudy eyes (corneal clouding)
The eyes frequently become cloudy, hazy, opaque, and/or white-colored in the circular part around the pupil. Patients may develop a hard time seeing things.
Hernia (bulge or lump in the belly button area or in the groin)
Many patients with MPS develop one or more hernias (bulges) at some point in their life. These hernias can occur in the belly button area (umbilical hernia), the groin (inguinal hernia), or both sites.

Snoring,  uncomfortable sleep, daytime sleepiness and fatigue
Some patients with MPS suffer from loud snoring, noisy breathing at night, and uncomfortable sleep. Patients are sometimes found to have sleep apnea (a type of sleep disorder in which an individual person holds or stops his breathing for many seconds while asleep).

Short Statue
Typically patients are short, normally less than 120cm/ 4 feet.

Change in facial appearance
Change in their facial appearance over time. This development, sometimes referred to as coarse facies or coarse facial

Hearing difficulty
Over time, the hearing loss can worsen to the point of needing a hearing aid. In severe cases, deafness can develop.

Heart murmurs, heart valve abnormalities
Defects of the heart valves which can be identified by doctors through an echocardiogram (heart ultrasound). In some individuals, heart murmurs (abnormal heart sounds) can be heard by a doctor performing a stethoscope examination. The heart valve problems can worsen to the point of requiring valve surgery.

Frequent ear, nose, and throat problems
Frequent infections, such as colds, ear infections, or sinus infections. May often leads to chronic problems in the ear, nose, or throat. Symptoms can include constant or frequent runny nose, stuffy nose, blocked nasal passages, sinus congestion, headaches, ear ache, sensation of ears being blocked, mucus problems, postnasal drip (having to clear the throat frequently), or sore throat. Due to frequent ear infections, patients sometime require tubes placed in their ears to drain the fluid behind the ear drum or even a myringotomy (surgical procedure to poke a small hole in the eardrum to relieve the pressure behind it). In addition, other surgeries might be required, such as tonsillectomy or adenoidectomy, to remove them because tonsils or adenoids become too large.

Large head
The head can be big in some patients and may grow larger over time.

Large tongue
The tongue can sometimes be unusually large. Because the tongue is so big, a patient might often stick their tongue out.

Delayed mental development
Delays in oral language development , deficits in memory skills, difficulty learning social rules, difficulty with problem solving skills, delays in the development of adaptive behaviors such as self-help or self-care skills and lack of social inhibitors.

Diagnosis

Diagnosis often can be made through clinical examination and urine tests (excess mucopolysaccharides (or GAGs) are excreted in the urine). Enzyme assays (testing a variety of cells or body fluids in culture for enzyme deficiency) are also used to provide definitive diagnosis of one of the mucopolysaccharidoses. Prenatal diagnosis using amniocentesis and chorionic villus sampling can verify if a fetus either carries a copy of the defective gene or is affected with the disorder. Genetic counseling can help parents who have a family history of the mucopolysaccharidoses determine if they are carrying the mutated gene that causes the disorders.

Treatment

Enzyme replacement therapy (ERT) is currently in use non neurological involved patients. Enzyme replacement therapy has proven useful in reducing non-neurological symptoms and pain. Currently Elaprase is used for MPS type I.

Bone marrow transplantation (BMT) and umbilical cord blood transplantation (UCBT) have had limited success in treating the MPS. Abnormal physical characteristics, except for those affecting the skeleton and eyes, may be improved, but neurologic outcomes have varied. BMT and UCBT are high-risk procedures and are usually performed only after family members receive extensive evaluation and counseling.

Surgery to remove tonsils and adenoids may improve breathing among affected individuals with obstructive airway disorders and sleep apnea. Sleep studies can assess airway status and the possible need for nighttime oxygen. Some patients may require surgical insertion of an endotrachial tube to aid breathing. Surgery can also correct hernias, help drain excessive cerebrospinal fluid from the brain, and free nerves and nerve roots compressed by skeletal and other abnormalities. Corneal transplants may improve vision among patients with significant corneal clouding.

Inheritance Pattern
 


As the figure above describes, any child born of 2 carrier parents has a three out of four (or 75%) chance of having at least one normal gene, and therefore no disease, and a one out of four (or 25%) chance of inheriting both defective gene from the parent and thus affected with the disorder. There is also a two out of three (or66%) chance that an unaffected offspring will still be a carrier of the defective gene that causes MPS I.

An affected person usually has unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers) (illustration). Autosomal recessive disorders are typically not seen in every generation of an affected family.



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