MPS IVA, Morquio A Disease
What else is it called?
- Morquio-Brailsford A disease
- Morquio A Disease
- Morquio A Syndrome
- Morquio’s A Disease
- Morquio’s A Syndrome
- MPS IVA
- mucopolysaccharidosis (MPS) IVA
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What causes it?
MPS IVA is caused by mutations (changes) in the GALNS gene. This gene provides instructions for producing enzymes that play a role in the breakdown of large sugar molecules called glycosaminoglycans (GAGs), formally known as mucopolysaccharides.
Mutations (changes) in the GALNS gene reduces or eliminates the activity of the enzymes produced from the gene. This leads to a build-up of GAGs within the cells, inside the lysosomes. Lysosomes are sections in the cell that break down and recycle different types of molecules. In this condition, GAGs build up to toxic levels in different tissues and organs, in particular the bones. This leads to bone deformities associated with this disorder.
The two types of MPS IV (A and B) are linked to mutations in different genes but in general cannot be distinguished by their signs and symptoms.
How common is it?
The exact prevalence of MPS IVA in unknown. However, the prevalence of MPS (A and B combined) is estimated to be between 1 in 200,000 live births to 1 in 300,000 live births.
What are the signs and symptoms?
MPS IVA is a progressive condition. The rate at which the symptoms worsens varies from patient to patient. Symptoms usually first start during early childhood. The symptoms are mainly symptoms affecting the skeleton and may include:
- short stature (height considerably below average)
- knock knees
- abnormalities of the ribs, chest, spine, hips and wrists
- hypermobile joints (loose and very flexible)
- restricted movement in certain joints
- Odontoid hypoplasia (the underdevelopment of a bone in the neck) which can lead to:
- Misalignment of the cervical vertebrae
- Compressed spinal cord
- Damaged spinal cord
- May lead to paralysis or death
Other symptoms may include:
- Cloudy vision/ vision loss
- Narrow airway leading to:
- Frequent upper respiratory infections
- Short pauses in breathing during sleep (sleep apnoea)
- Mildly coarse facial features
- Thin tooth enamel
- Multiple cavities
- Heart valve abnormalities
- Hepatomegaly (mildly enlarged liver)
- Umbilical hernia (a soft out-pouching around the bellybutton)
MPS IVA does not affect intelligence
How is it diagnosed?
MPS IVA is diagnosed based on the findings of the patient’s full medical history, physical exam, skeletal X-rays and specialised urine tests. Individuals with this condition will show excessive amounts of keratan sulfate in the urine.
The diagnosis is confirmed through molecular genetic testing which will show mutations in GALNS gene.
Can it be treated?
A recently approved (2014) treatment for MPS IVA is human GALNS enzyme replacement therapy. Other treatments for this condition are symptomatic and supportive, aiming to manage and alleviate individual symptoms and to provide support for the patients and their families.
Surgery may be necessary to decompress (expand) and fuse (merge) the bones of the upper neck to the base of the skull. This is to prevent destabilization of the cervical vertebrae and damage to the spinal cord.
Do my family need to be tested?
MPS IVA is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of MPS IVA is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with MPS IVA are carriers.
When both parents are carriers, the risk to the baby in each pregnancy is
- 25% chance (1 in 4) of developing the condition
- 50% chance (1 in 2) for the baby to be a carrier of the condition
- 25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier
Genetic counselling can be requested to get a full explanation.