Background
Mucopolysaccharides consist of glycosaminoglycans attached to a link protein with a hyaluronic acid core. Lysosomal enzymes degrade these macromolecules into smaller components. Heparan sulfate, dermatan sulfate, and keratan sulfate are by-products of an incomplete degradation process. The accumulation of these compounds interferes with cell function.
Different forms of the disease were described separately throughout the 20th century. Their clinical presentations are varied depending on the type of enzyme defect and glycoprotein accumulated.
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An image depicting Morquio syndrome can be seen below.
An 8-year-old boy with Morquio syndrome and severe kyphoscoliosis. Courtesy of Dennis P. Grogan, MD. Pathophysiology
Defective activity of the lysosomal enzymes blocks the degradation process of mucopolysaccharides, leading to abnormal accumulation of heparan sulfate, dermatan sulfate, and keratan sulfate. These degradation by-products are then secreted and detected in the urine. Mucopolysaccharidosis (MPS) can be subclassified according to the type and amount of substance that accumulates, as follows: Hurler syndrome (MPS IH) (see the first 3 images below), Hurler-Scheie (MPS I-H/S), Scheie syndrome (MPS IS), Hunter syndrome (MPS II), Sanfilippo syndrome (MPS III), Morquio syndrome (MP IV) (see the latter 5 images below), Maroteaux-Lamy syndrome (MPS VI), and Sly syndrome (MPS VII).[1, 2, 3]
Hurler syndrome; lateral radiograph of thoracolumbar vertebrae illustrates vertebral plana. Courtesy of Bruce M. Rothschild, MD. 
Hurler syndrome; widened metaphyses and diaphyses with truncated distal portions forming a peg characterize this radiograph. Courtesy of Bruce M. Rothschild, MD. 
Hurler syndrome; widened metaphyses and diaphyses with truncated distal portions forming a peg characterize this radiograph. Courtesy of Bruce M. Rothschild, MD. An 8-year-old boy with Morquio syndrome and severe kyphoscoliosis. Courtesy of Dennis P. Grogan, MD. 
A 7-year-old girl with Morquio syndrome and typical severe genu valgum. Courtesy of Dennis P. Grogan, MD. 
Morquio syndrome; widened bases of phalanges with osteopenia. Courtesy of Bruce M. Rothschild, MD. 
Morquio syndrome; lateral radiograph of thoracolumbar vertebrae illustrates vertebral body beaking. Courtesy of Bruce M. Rothschild, MD. 
Morquio syndrome; anteroposterior radiograph of pelvis illustrates avascular necrosis of femoral head. Courtesy of Bruce M. Rothschild, MD. Epidemiology
Frequency
International
The prevalence of all types of MPS is 1 case in 16,000-30,000 births. MPS III accounts for 80% of cases. These syndromes are found in persons of all ethnic groups, but prevalence is increased in Israeli Jews and French Canadians.
Mortality/Morbidity
These disease processes have significant effects on the growth and development of the musculoskeletal system, including joint stiffness or hyperlaxity, deformities, and progressive loss of function. Multiple other organ systems are involved. The type and extent of organ system involvement are variable depending on the subset of the disease. Most of these patients have shortened life spans and some of them die in infancy.
Race
These syndromes are found in all ethnic groups. Incidence of MPS II is increased in Israeli Jews, and incidence of MPS IV is increased in French Canadians.
Sex
All mucopolysaccharidoses are inherited as autosomal recessive disorders with the exception of Hunter syndrome (MPS II), which is inherited as sex-linked recessive condition. Thus, all patients with Hunter syndrome are males.
Age
Ages at which features of MPS present are somewhat variable. MPS features mostly present in the first few months of life. However, Morquio syndrome usually presents in children aged 2-4 years, and MPS IS and MPS VI can present late in childhood.
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