Morquio syndrome is a rare, inherited metabolic disorder that most often affects the skeleton. Also known as MPS IV, Morquio syndrome is part of a group of diseases called mucopolysaccharidosis (MPS). MPS is defined by the body’s inability to break down large sugar chains called glycosaminoglycans (formerly known as mucopolysaccharides). As a result, these molecules build up in the body and interfere with cell function.
Prevalence
It’s unknown how many people are affected by MPS IV. Some estimates place the rate at about 1 in 210,000 people, according to a case report in the journal Joint Bone Spine. The prevalence of the disorder also varies greatly by population. For instance, it may occur in as many as 1 in 43,261 births among the Turkish population living in Germany, but in as few as 1 in 1,505,160 births in Sweden, according to a 2010 article in the Orphanet Journal of Rare Diseases. Morquio affects males and females equally, and no ethnic group — broadly speaking — appears to have an increased risk for the disorder.
Types and Causes of Morquio Syndrome
There are two forms of Morquio syndrome: Type A and Type B. Morquio A syndrome, or MPS IVA, results from a deficiency in the enzyme galactosamine (N-acetyl)-6-sulfatase (GALNS). Morquio B syndrome (MPS IVB), which is rarer and less severe than MPS IVA, results from a deficiency in the enzyme beta-galactosidase. Without either of these enzymes, the body cannot break down certain glycosaminoglycans, particularly keratan sulfate. Morquio syndrome is an autosomal recessive trait, meaning that you can only develop the disorder if you inherit two mutated genes — one from your mother and one from your father. Neither parent will likely show any signs or symptoms of the condition.
Symptoms and Complications
Glycosaminoglycans play an important role in building healthy bone, cartilage, corneas, skin, and connective tissue, including tendons and ligaments. People with Morquio syndrome may experience issues with any of these body parts. Symptoms, which usually begin between ages 1 and 3, may include:
Short stature with a long torsoAbnormal bone and spine development, including a curved spine (severe scoliosis)Bell-shaped chest, with ribs that flare out at the bottomUnusually flexible joints (hypermobile joints, also known as being double-jointed)Knock-knees, or knees that angle inward and touch each other when the legs are straightTeeth spaced widely apartAbnormally large head (macrocephaly)“Coarse” facial features, such as a bulging foreheadCloudy visionHeart valve issues and heart murmurEnlarged liver
Over time, MPS IV may cause serious complications, including:
Spinal cord damage, which may result in paralysisBlindnessBreathing problems and narrowed airways, which may cause frequent upper respiratory infectionsHeart failureHearing impairment
Unlike some other types of MPS, Morquio syndrome doesn’t appear to cause intellectual disabilities.
Morquio Syndrome Diagnosis and Treatment
Diagnosis of Morquio syndrome typically begins with a physical examination, which can reveal various telltale signs of the disorder. If you have signs or symptoms of MPS, your doctor will likely order a urine test to see if you have high levels of glycosaminoglycans. Additional culture tests can detect unusual enzyme activity, and genetic tests (using saliva or blood) can reveal mutations indicative of MPS IV. There is no cure for Morquio syndrome, and treatment is limited to supportive care of symptoms. For example, physical therapy and surgical procedures, such as spinal fusion, may help with scoliosis and other bone and muscle issues. In 2014, the Food and Drug Administration (FDA) approved the drug Vimizim (elosulfase alfa) for the treatment of MPS IVA. Vimizim provides the body with the GALNS it’s missing, helping to improve physical endurance. Morquio syndrome can significantly shorten a person’s lifespan due to spinal cord compression and breathing complications. People with severe cases of MPS IV may only live into their twenties or thirties, and even people with mild cases don’t often live beyond age 60, according to a 2013 study in the journal Molecular Genetics and Metabolism.
