Term / Mucopolysaccharidoses (MPS)

Mucopolysaccharidoses (MPS) are part of the family of approximately 50 inherited disorders called lysosomal storage disorders that occur when a missing enzyme results in the body’s inability to recycle cellular waste. Enzymes are special types of proteins required to break down food molecules into fuel during metabolism, the process by which the body gets energy for normal growth and development. Enzyme deficiencies, or the absence of these enzymes, result in a number of life-changing or life-threatening conditions.

The missing enzymes in MPS cause complex sugar molecules called glycosaminoglycans (GAGs) to accumulate in cells. GAGs are long, repeating chains of complex sugar molecules that are normal chemical components of bones, cartilage, and many other tissues within the body. They are constantly being “turned over,” meaning that new GAGs are produced as others are broken down. If the GAGs cannot be broken down normally, they accumulate in various tissues of the body. As a result, progressive damage is done to the heart, bones, joints, respiratory system and central nervous system.

While the disease may not be apparent at birth, signs and symptoms develop with age as more cells become damaged.  It is estimated that one in every 25,000 babies born in the U.S. has some form of MPS.

The MPS disorders are categorized into several groups based on the clinical features and specific enzyme deficiency. An individual is usually suspected of having an MPS disorder after developing characteristic physical findings, which vary depending on the specific diagnosis. While the symptoms of the diseases may vary from one syndrome to another, there are similarities. Affected individuals may have mental retardation, cloudy corneas, short stature, stiff joints, incontinence, speech and hearing impairment, chronic runny nose, hernia, heart disease, hyperactivity, depression, pain and a dramatically shortened life span.

Depending on the subtype, affected individuals may have normal intellect or have cognitive impairments, may experience developmental delay or have severe behavioral problems. Many individuals have hearing loss. Communicating hydrocephalus – in which the normal reabsorption of cerebrospinal fluid is blocked and causes increased pressure inside the head – is also common in some of the mucopolysaccharidoses.

Physical symptoms generally include coarse or rough facial features (including a flat nasal bridge, thick lips and enlarged mouth and tongue), short stature with disproportionately short trunk (dwarfism), dysplasia (abnormal bone size and/or shape) and other skeletal irregularities, thickened skin, enlarged organs such as liver (hepatomegaly) or spleen (splenomegaly), hernias and excessive body hair. Short and often claw-like hands, progressive joint stiffness, and carpal tunnel syndrome can restrict hand mobility and function. Recurring respiratory infections are common, as are obstructive airway disease and obstructive sleep apnea. Many affected individuals also have heart disease, often involving enlarged or diseased heart valves.

MPS disorders include: