An Overview of Morquio Syndrome

Morquio syndrome is a congenital disorder that impacts skeletal development.

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A rare genetic metabolic disorder, Morquio syndrome is a condition in which the body is unable to process certain types of sugar molecules (glycosaminoglycans). Also known as mucopolysaccharidosis type IV (MPS IV), this disease expresses as a predominantly skeletal disorder, leading to an abnormal curvature of the spine, short neck, knock knees, and hip problems. In affected children, the syndrome may present with an enlarged head and characteristic facial features. The condition is usually diagnosed in infants. Supportive care is needed for the management of physical effects. Intellectual abilities are not affected by this condition.

Symptoms

As a disorder caused by metabolic abnormalities, Morquio syndrome has a wide range of effects, though the most common are in the skeletal system. Arising first in early childhood, initial symptoms are primarily skeletal in nature, including:

  • Shorter stature: Growth delays are frequent symptoms of the condition as it leads to abnormal epiphyses and development of the long bones.
  • Knock knees: Those with the condition have knees that are closer together.
  • Hip problems: Since the syndrome affects bones and related tissues, it leads to excessive mobility of the hips, which can cause dislocation. Arthritis can also develop there.
  • Hypermobility: In most cases, this condition leads to excessive mobility and instability in the wrists, knees, elbows, and other joints.
  • Neck issues: A consistent issue with Morquio syndrome is underdevelopment (hypoplasia) of the odontoid bone in the neck (cervical vertebrae). This leads to instability in the region and can cause compression of the spinal cord, which can lead to paralysis or even death.
  • Flat feet: Another characteristic of the condition is flattening in the feet, which can affect gait.
  • Chest deformity: Some cases of this disease lead to underdeveloped of the rib cage, which can compress the lungs and heart. 
  • Growth abnormalities: Children with the condition often have an abnormal short trunk and normal-sized limbs.
  • Flattened vertebrae: X-ray scans of those with the condition reveal vertebrae (bones of the spine) that are significantly flatter than usual.
  • Larger skull: The skulls of people with this disorder are comparatively larger than average.

Beyond skeletal issues, Morquio syndrome also has a range of other effects in the body:

  • Facial features: Those with the condition often have a very small nose, prominent cheekbones, a broad mouth, wider-set eyes, and a generally larger than usual head.
  • Hearing loss: Reduction in or complete absence of ability to hear is also noted in some cases.
  • Clouding of eyes: Some with the condition may develop clouding over the corneas of eyes.
  • Abnormal teeth: Dental issues that arise as a result of Morquio syndrome include widely-spaced teeth with a thinner than usual layer of enamel.
  • Enlarged organs: In some cases, the liver and spleen of those affected are somewhat larger than usual.
  • Reduced life span: In more severe instances with more pronounced symptoms, those with this condition are not expected to survive past adolescent. Survivability is better for more mild cases, with most living well into adulthood, though lifespan is still affected.

Varying in severity, this disorder affects men and women at the same rate and is seen in anywhere from one in 200,000 to 300,000 births.

Causes

Morquio syndrome is a genetic disorder, and it results from mutations of two specific genes: GALNS and GLB1. Primarily, these are involved in the production of enzymes that digest larger sugar molecules called glycosaminoglycans (GAGs). Though these present as nearly identical, type A of this disease refers to mutations of the GALNS gene, whereas type B occurs when GLB1 is affected.

Basically, when the affected digestive enzymes are not functioning properly, GAGs build up within lysosomes, the parts of cells that break down and recycle molecular components. This can become a toxic situation, with effects being particularly pronounced in bone cells and eventually lead to deformities.

This disease is what’s called an autosomal recessive disorder, meaning that two copies of the abnormal gene are needed: one from each parent. Those who have only one such gene are carriers of Morquio syndrome and will not display symptoms. If both parents have this abnormality, the chance of the child having the condition is 25 percent.     

Diagnosis

This disease is often initially diagnosed through physical examination, as infants will begin to display physical symptoms, along with an assessment of medical history. X-rays or other kinds of imaging can let doctors see the impact on bones and joints.

Doctors can analyze levels of GAGs in the urine, with higher levels being a potential sign of Morquio syndrome. Types A and B of this disease can be detected through molecular genetic testing of GALNS and GLB1 enzyme activity, respectively; this is usually done once doctors have other reasons to suspect the condition.

Treatment

The first line of treatment of Morquio syndrome involves the management of physical symptoms, which often entails a multi-faceted approach across several different medical specialties. Physical and occupational therapists, surgeons, and other kinds of doctors coordinate efforts to ensure the best outcomes. These might include:

  • Decompression surgery: Since compression of the upper neck and base of the skull due to skeletal deformity is a frequent issue, doctors may need to perform surgery to ease this pressure and improve stability in the region.
  • Cardiac surgery: When the heart is constricted by the narrower, less-developed rib cage that accompanies the condition, the surgical placement of a prosthetic valve may be needed.
  • Airway procedures: Disruptions to airways is one of the most dangerous aspects of Morquio syndrome. Doctors, therefore, may need to surgically remove enlarged tonsils and adenoids.
  • Corneal replacement: In those that develop clouding in the eyes, surgeons may indicate the need for corneal replacement (keratoplasty).
  • Approaches to hearing loss: Hearing loss is a common attribute of this condition, so hearing aids may be needed for those with it. In some cases, surgeries to place ventilation and auditory tubes may be needed.
  • Occupational considerations: Most with this condition display normal intelligence, so special education classes are not needed. However, accommodations are important; students with this syndrome should be seated towards the front. As the condition progresses, skeletal instability increases, so walking aids or wheelchairs may be needed.
  • Enzyme treatment: Type A Morquio syndrome cases can be treated with specialized medications that help replace GALN enzyme levels. This is done intravenously. 
  • Genetic counseling: Those in families with a history of this condition should consider genetic testing and counseling. This will help lay out risks of transmission and those expecting or planning to have kids with risk assessment.

Coping

There’s no doubt that Morquio syndrome, with its cascading and significant effects, can represent a challenging burden both for those experiencing it and their families. Certainly, there can be an emotional fallout in these cases, so mental health counseling may be needed both for the person affected and those around them. In psychiatry, there are specialists that focus on taking on issues related to medical conditions. Furthermore, support groups, such as The National MPS Society, can foster community and help raise awareness about the condition.

A Word From Verywell

Genetic conditions are always challenging. Since there is as yet no complete cure for Morquio syndrome—and since it’s a progressive condition—facing the disease can be very daunting. However, it’s important to note that the symptoms of this condition can be managed, and researchers are learning more and more about it. What this means is that approaches to this disease are continuing to evolve and improve; we’re better than we’ve ever been at taking it on, and it’s only going to get better. 

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Article Sources

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  1. National Organization for Rare Disorders. Mucopolysaccharidosis IV. Published 2019. 

  2. National Institutes of Health. Mucopolysaccharidosis type IV. Genetics Home Reference. Published 2019.

  3. National MPS Society. MPS and ML Disease Information, Donations, and Support. MPS Society. Published 2019.