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Mysterious Mucopolysaccharidoses: What's the truth behind these rare diseases?
Mucopolysaccharidoses (MPS) are a group of metabolic diseases caused by deficient or malfunctioning lysosomal enzymes. These enzymes are essential for breaking down molecules called glycosaminoglycans (GAGs). GAGs are found inside cells and help build bones, cartilage, tendons, corneas, skin and connective tissues, and also play an important role in the fluid that lubricates joints. When an individual is unable to produce enough of the required enzymes, or when their enzymes malfunction, GAGs accumulate in body cells and blood, causing persistent and progressive cell damage that affects appearance and body function.
"Lysosomes can be thought of as the recycling center of the cell, processing unwanted substances and converting them into other substances that can be used."
Symptoms and Signs
The manifestations of mucopolysaccharidosis vary in severity, and many symptoms are not obvious at birth but gradually appear as GAGs accumulate. These symptoms can include damage to the nervous system, pain, limited motor function, and impaired cognitive abilities. As the disease progresses, hearing loss, vision problems, or behavioral abnormalities may occur. Common physical signs include coarse facial features, short stature, thickening of the skin, and enlargement of certain organs.
"Physical symptoms often include short stature, disproportionate body parts, and progressive joint stiffness."
Genetics
An estimated 1 in 25,000 newborns in the United States will have some form of mucopolysaccharidosis. Most mucopolysaccharidoses are autosomal recessive disorders, meaning that a child will be affected only if both parents carry the defective gene. For some parents with a family history of mucopolysaccharidosis, genetic counseling can help them determine whether they carry the mutated gene that causes the disease.
Diagnosis
Diagnosis is usually made through clinical examination and urine testing. Excess mucopolysaccharides are usually excreted in the urine. Enzyme activity tests are also used to identify specific types of mucopolysaccharidosis. Prenatal diagnosis can be done through amniocentesis and chorionic villus sampling to verify whether the fetus carries the defective gene or is already affected.
Different types
Seven distinct clinical types and multiple subtypes of mucopolysaccharidosis have been recognized. Each type is clinically unique; however, most patients experience a period of normal progression followed by a decline in physical or mental function.
MPS I
MPS I is divided into three subtypes based on the severity of its symptoms. All three types are caused by the absence or deficiency of α-L-pyranosidase.
MPS II
MPS II, or Hunter syndrome, is caused by a deficiency of the enzyme iduronate sulfatase and is the only mucopolysaccharidosis that can be passed from mother to son.
MPS III
Also known as Simfilippo syndrome, it is characterized by severe neurological symptoms that usually appear in childhood and gradually worsen over time.
MPS IV
Morquio syndrome, which occurs in 1 in 700,000 births, has neurological complications that can affect growth and development.
MPS VIMarauder-Ramie syndrome is a milder form of the disease, usually with normal intelligence, but with many physical symptoms similar to those of Heckler syndrome.
MPS VIISly syndrome is the least common of the mucopolysaccharidoses, affecting approximately 1 in 250,000 births.
TreatmentThere is currently no cure for these diseases, and medical care focuses on treating systemic conditions to improve the patient's quality of life. Physical therapy and daily exercise can slow joint problems and improve mobility. Some patients may receive enzyme replacement therapy to reduce non-neurological symptoms and pain.
“These diseases not only affect the normal function of the body, but also pose significant challenges to the lives of patients and their families.”
So, with such complex and mysterious diseases, how can we better support patients and families with these rare diseases?
