Morquio syndrome is a rare inherited condition in which the body cannot break down a specific type of sugar chain found in cartilage, bone, and the cornea of the eye. Without the enzyme needed to process these chains, partially digested molecules accumulate in cells throughout the body, progressively damaging the skeleton, joints, heart, airways, and eyes. Birth prevalence ranges from roughly 1 in 71,000 to 1 in 500,000 depending on the country and diagnostic methods used, making it one of the rarer forms of mucopolysaccharidosis (MPS IV).
Types A and B
Morquio syndrome comes in two forms, both inherited in an autosomal recessive pattern, meaning a child must receive a faulty gene copy from each parent.
- Type A (MPS IVA) results from a deficiency of an enzyme called GALNS. This enzyme normally removes sulfate groups from sugar chains in cartilage and bone. Without it, a molecule called keratan sulfate builds up in tissues. Type A is the more common and typically more severe form.
- Type B (MPS IVB) results from a deficiency of a different enzyme called GLB1. The buildup is similar but usually produces milder symptoms.
Because both types block the same cleanup pathway at different steps, their symptoms overlap considerably. The key difference is which gene carries the mutation and how much residual enzyme activity a person retains, which influences severity.
How the Body Is Affected
The sugar chains that accumulate in Morquio syndrome are concentrated in cartilage and connective tissue, so the skeleton bears the heaviest burden. Children with the condition develop what clinicians call short-trunk dwarfism: the limbs are relatively normal in length, but the torso is compressed. A prominent, outward-jutting breastbone (pectus carinatum) gives the chest a barrel shape, and the spine often curves sideways or forward. Loose ligaments make joints unusually flexible, and knock knees are common because the lower ends of the thighbone and upper ends of the shinbone grow unevenly.
The vertebrae themselves become flattened and irregularly shaped. One of the most dangerous skeletal changes involves the top of the spine: the small bony peg that keeps the first two neck vertebrae aligned (the odontoid process) is underdeveloped in nearly all patients. This creates instability at the very top of the neck, where the spinal cord meets the brainstem. Even a minor fall or sudden neck movement can compress the spinal cord at this point, causing episodes of sudden limb weakness, difficulty walking, or in severe cases, paralysis. Screening for this instability is a critical part of ongoing care.
Beyond the Skeleton
Although bone and joint problems dominate the picture, Morquio syndrome affects multiple organ systems as sugar chains accumulate in softer tissues.
The eyes are commonly involved. Diffuse corneal clouding is the most frequent finding, though it tends to be milder and slower to progress than in other types of MPS. Vision problems such as astigmatism, nearsightedness, farsightedness, and cataracts can develop over time, gradually reducing visual clarity as patients get older.
Heart valve disease is surprisingly common. In one dedicated study, half of patients had leaking of the mitral valve, 30 percent had aortic valve leaking, and 40 percent had noticeable thickening of one or both valves. These changes can worsen over decades and may eventually require surgical intervention.
Airway and lung problems round out the picture. A narrowed windpipe, softening of the airway cartilage (tracheomalacia), obstructive sleep apnea, and a combination of restrictive and obstructive lung disease all contribute to breathing difficulties. Hearing loss, abdominal hernias, liver enlargement, and dental abnormalities are also reported.
How Morquio Syndrome Is Diagnosed
Diagnosis usually begins when a child shows the characteristic skeletal features, often between ages one and three. The first screening step is a urine test measuring keratan sulfate levels. A more sensitive laboratory method using mass spectrometry detects elevated keratan sulfate in all confirmed cases, while the older total glycosaminoglycan test misses roughly 17 percent of patients. An abnormal urine result always needs to be confirmed by measuring enzyme activity in blood or skin cells, which provides a definitive diagnosis. Genetic testing can then identify the specific mutations in either the GALNS or GLB1 gene, which is also useful for carrier testing in family members.
Treatment Options
For Type A, an enzyme replacement therapy called elosulfase alfa has been available since 2014. It works by supplying the missing GALNS enzyme through a weekly intravenous infusion, given over about 3.5 to 4.5 hours each session. The treatment can improve endurance and walking ability, though it does not reverse skeletal damage that has already occurred. Starting treatment early in life, before significant bone changes set in, offers the best chance of preserving function.
No enzyme replacement therapy currently exists for Type B.
Surgical management plays a major role regardless of subtype. Spinal fusion at the top of the neck is frequently needed to stabilize the atlantoaxial joint and protect the spinal cord. Joint surgeries, spinal corrections, and procedures to address airway narrowing are common throughout a patient’s life. Regular cardiac monitoring, pulmonary function testing, eye exams, and hearing assessments form the backbone of ongoing surveillance.
Life Expectancy and Outlook
Morquio syndrome significantly shortens life, though outcomes have been improving. In a large study of mortality data, the mean age at death was about 25 years. Female patients lived slightly longer on average (around 27 years) compared to male patients (around 23 years). Respiratory failure accounted for nearly two-thirds of deaths, followed by cardiac failure, complications of surgery, and post-traumatic organ failure, each at about 11 percent.
The encouraging trend is that survival has been steadily climbing. The mean age at death from respiratory failure rose from about 17 years in the 1980s to nearly 31 years in the 2000s, reflecting improvements in airway management, surgical techniques, and the introduction of enzyme replacement therapy. People with milder forms of the condition, particularly those who retain some residual enzyme activity, can live well into adulthood with careful multidisciplinary care.