Morquio Type A vs. Type B: What is the Difference?

Morquio syndrome, also known as Mucopolysaccharidosis type IV (MPS IV), is divided into two types: Type A and Type B. Both types are inherited in an autosomal recessive pattern, meaning a child must inherit the mutated gene from both parents ^[1]. While both types cause similar bone and skeletal changes because they affect how the body breaks down complex sugars—specifically keratan sulfate (and chondroitin-6-sulfate in Type A)—they are caused by different deficient enzymes and have different treatment options ^[1]. In general, Type A is more common and often more severe, whereas Type B is typically milder and does not currently have an approved enzyme replacement therapy ^[1]. Doctors distinguish between the two types using blood tests to measure enzyme activity or genetic testing ^[2].

The Biology: Different Deficient Enzymes

Every person with Morquio syndrome does not have enough of a specific working enzyme needed to break down sugars in the body’s cells. The exact enzyme that is deficient determines the type of Morquio syndrome:

• Morquio Type A: Caused by mutations in the GALNS gene, leading to a deficiency of an enzyme called N-acetylgalactosamine-6-sulfatase ^[1].
• Morquio Type B: Caused by mutations in the GLB1 gene, leading to a deficiency of an enzyme called beta-galactosidase ^[1].

Severity and Physical Differences

Both types present with dysostosis multiplex, the medical term for the widespread bone and skeletal changes seen in MPS conditions ^[1]. This includes joint laxity (loose joints), spinal curvature (kyphoscoliosis), and issues with the bones in the neck ^[1].

However, how the condition develops differs between the two:

• Growth and Stature: While both types cause growth impairment, the skeletal changes in Type B are generally milder than in Type A ^[1]. Adults with Type B are typically taller than adults with Type A, although they still usually have a final height well below average ^[1].
• Neurological Symptoms: Morquio Type A typically does not directly affect a person’s cognitive function or brain health. “Pure” Morquio Type B also only involves skeletal features ^[1]. However, Morquio Type B is genetically linked to another condition called GM1-gangliosidosis ^[1]. Some rare individuals have “Morquio B plus,” a variant that includes neurological symptoms like delayed cognitive development, balance issues, or involuntary muscle contractions ^[1]. It is important to know that classic Morquio B does not impact intelligence.

Treatment Options and Daily Life

One of the most crucial differences for patients and families to understand is the availability of targeted treatments, though both require extensive day-to-day management.

• Treating Type A: There is an FDA-approved Enzyme Replacement Therapy (ERT) for Morquio Type A, known as elosulfase alfa (Vimizim). This treatment works by providing the body with the GALNS enzyme it is missing, which has been shown to stabilize or improve endurance and lung function, protecting certain organs ^[3][4]. However, ERT does not cure the condition or stop the progression of bone and skeletal changes, because it cannot easily reach bone tissue.
• Treating Type B: Currently, there is no approved ERT for Morquio Type B ^[1]. Because Type B is caused by a different deficient enzyme, the ERT used for Type A will not work for Type B patients. Researchers are actively exploring future treatments like gene therapy for both types ^[5].

Living with Morquio Syndrome

Regardless of whether a patient has Type A or Type B, the condition involves significant daily realities. Active management by a care team often means addressing chronic pain and preparing for major orthopedic surgeries, such as spinal fusions or leg procedures, to maintain mobility and protect the spinal cord ^[1][6]. Day-to-day quality of life is heavily supported by physical therapy and mobility aids—like wheelchairs, scooters, or walkers—to help conserve energy and maintain independence.

A coordinated care team of specialists (including orthopedists, cardiologists, and pulmonologists) is essential to manage complications, such as spinal cord compression, vision issues from corneal clouding, and heart valve problems ^[1][6].