Genetics Northern California

Morquio Syndrome

Morquio syndrome is a disorder of mucopolysaccharides (a specific sugar) storage. Mucopolysaccharides are vital in the building of cartilage, skin, tendons, and many other tissues. In Morquio syndrome, the enzyme that is responsible for breaking down the old mucopolysaccharides is deficient, leading to a buildup of mucopolysaccharides in many of the body's tissues. This buildup causes damage to these tissues resulting in the clinical features of Morquio. Morquio is characterized by short stature (adult height = 80-120 cm), severe bone disease and preservation of intelligence. Systems affected include facial features, pulmonary, dental, part, liver and spleen, joints, ears, and eyes. Common medical concerns include clouding of the cornea of the eyes, hearing loss, abnormal tooth enamel, cervical spine instability, kyphoscoliosis (curves of the spine), breathing problems, mild heart disease, joint hypermobility, knock knees, hip changes (coxa valga), pes planus (flat feet), and adult-onset arthritis.

Causes
There are two enzyme deficiencies that can lead to the buildup of keratan sulfate in cells. This leads to two different types of Morquio syndrome: A & B. Both are very similar clinically with B often being milder than A. Type A is due to a deficiency of N-acetylgalactosamine-6-sulfatase and Type B is the result of a deficiency in beta-galactosidase. The deficiency and either leads to a buildup of keratan sulfate in the tissues. Morquio syndrome is inherited as an autosomal recessive condition.

Diagnosis
Symptoms/features of Morquio syndrome usually present between ages 1 and 3 years, but a diagnosis is often not made until ages 3-10. Early features include gait (walking) abnormality, abnormal leg positioning, and decrease in rate of growth. Screening for mucopolysaccharides is done by testing for the product that does not get broken down, which for Morquio is keratan sulfate. This screening can be done using urine or blood. An enzyme assay (testing to show the deficiency of the enzyme) is required to confirm the diagnosis and determine the type of Morquio syndrome (Type A or Type B). This test usually requires a skin biopsy.

Prenatal Diagnosis
Prenatal diagnosis for Morquio is available by amniocentesis or chorionic villi sampling (CVS) when one child in the family has been previously diagnosed with Morquio.

Treatment/Services
There is no cure for Morquio syndrome, but monitoring for early intervention is an important part of treatment. More recently enzyme replacement therapy has become a standard of care for Morquio. 

Preventive monitoring includes routine eye and ear exams as well as cardiac and respiratory studies (e.g., pulmonary function tests, sleep studies, echocardiograms). If problems are identified, treatment focuses on improving quality of life by addressing symptoms. These may include surgical correction of genu valgum (knock knees), physical and occupational therapy services to improve strength, mobility aids (e.g., scooters, wheelchairs, etc.), glasses to improve vision, hearing aids to overcome hearing loss, treatment of infections, prophylactic antibiotics to protect the heart, and fusion of the cervical spine, in cases of increased instability. 

Bone marrow transplant has been used with limited success in decreasing the severity of symptoms and improving life expectancy. 

Enzyme replacement therapy – This therapy is given by weekly infusion. It replaces the enzyme that is missing due to the gene defect that causes Morquio syndrome. ERT has become standard of care for Morquio syndrome. It seems to help most in the internal organs – liver, spleen and heart. The skeletal manifestations of Morquio syndrome do not seem to be impacted by this treatment. 

RESOURCES

The Carol Ann Foundation & International Morquio Organization - A non-profit organization dedicated to seeking out people who have Morquio Type A in order to provide a mutual aid network; act as a advocate between patients, physicians and scientists; compile medical information into a database; and pursue funding for education, families and research.

National MPS Society - The National MPS Society exists to find cures for MPS and related diseases. They also provide hope and support for affected individuals and their families through research, advocacy and awareness of these diseases.

Morquio syndrome - General information about Morquio syndrome from Medline Plus, a service of the National Library of Health and the National Institutes of Health.

Last reviewed: May 2020
Reviewed by: Ericka Okenfuss, LCGC