Mucolipidosis IV

What else is it called?

  • Ganglioside Sialidase Deficiency
  • ML4
  • MLIV
  • Sialolipidosis

Get in touch

Contact our caring team on 08452 412 173 for help and support. Our phone lines open 10am-4pm, Monday to Friday.

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What causes it?

This disorder belongs to a group called the Lysosomal Storage Disorders which are caused by an enzyme deficiency. Lysosomes are a part of the body’s cells and are responsible for digesting and assisting in recycling molecules.   A lack of an enzyme which is present in the lysosome causes fats and proteins to build up meaning that the cell cannot work properly.

This disorder is caused by problems in the MCOLN1 gene which is needed to produce a protein called Mucolipin-1.  This protein helps the cells in the body to transport fats and proteins between different parts of the cell. In this disorder, there is not enough of this protein produced and this prevents fats and proteins from being absorbed into the cell causing a build-up of substances in the lysosome. This leads to the cell not functioning correctly and results in the signs and symptoms of this disorder.

There is not a great deal known about the Mucolipin-1 protein. However, it appears to be important for the development and maintenance of the retina and is also believed to play a vital role in ensuring the proper function of the cells in the stomach which produce digestive acids.

How common is it?

This disorder is thought to affect approximately 1 person in every 40,000 people. There is a high carrier rate in individuals from Ashkenazi Jewish heritage and is therefore more common in this population.

What are the signs and symptoms?

There are two forms of this disorder, a severe form (typical Mucolipidosis IV), and a milder form (atypical Mucolipidosis IV). The severe form is by far the most common, representing approximately 95% of cases.

Signs and symptoms usually become apparent within 3-8 months after birth. This disorder is usually first investigated after the onset of symptoms affecting the movement of the eyes and clouding of the cornea.

Most infants with this disorder develop the following symptoms:

  • Low muscle tone (hypotonia) which progresses to muscle stiffness and difficulty controlling hand movements
  • Moderate to severe intellectual disability
  • Limited speech to a few words only, or absent speech.
  • Swallowing and chewing difficulties.

Significant delays in mental and motor developmental milestones are common which affects skills such as sitting, crawling, standing, walking and holding/grasping objects. These delays are recognisable in the first week of life and in approximately 15% of cases these symptoms are progressive. It is unlikely that independent walking will be possible, although some have increased mobility with the aid of a walker.

Symptoms affecting the eyes are common and slowly progressive. Vision is normal at birth. However, with progressive breakdown of the retina, vision is severely impaired or lost by early teenage years. Other eye problems may include:

  • Crossed eyes (strabismus)
  • Puffy eyelids
  • Increased sensitivity to light (photophobia)
  • Nearsightedness (myopia).
  • Eye pain which improves in frequency and severity with age
  • Involuntary eye movements (nystagmus)
  • Drooping of the eyelid (Ptosis)
  • Cataract

If you have Mucolipidosis IV, your body is unable to produce enough stomach acid (achlorhydria). This leads to high levels of a hormone called gastrin which regulates the production of stomach acid. In approximately 50% of cases, this leads to iron deficiency and a further 10% will go on to develop anaemia.

Progressive kidney failure may develop in the third decade of life.

Seizures are infrequent and may only occur in some individuals.

Those with the severe form usually survive into adulthood although may have a shorter than average lifespan. Atypical Mucolipidosis IV has milder and fewer symptoms. They have milder symptoms affecting motor skills and may develop the ability to walk.

How is it diagnosed?

This disorder should be suspected in any individual with breakdown of the retina and early delays in reaching developmental milestones or a progressive loss of abilities. It can be confirmed through blood tests, the presence of high gastrin levels in those with anaemia, and identification of the defects in the MCOLN1 gene using genetic testing. Other tests may include MRI, EEG and biopsies.

Can it be treated?

There is no cure for Mucolipidosis IV. Treatment is supportive and aims to manage specific symptoms. Treatment includes:

  • Speech therapy
  • Physiotherapy
  • Occupational therapy
  • Iron supplements
  • Ankle-foot orthotics (AFOs)

Eye symptoms can be managed using eye drops, artificial tears, gels, and/or contact lenses. Surgery can correct strabismus and cataracts.

Do my family need to be tested?

Humans have chromosomes composed of DNA. Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes. We inherit particular 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.

This is an inherited condition. There is nothing that could have been done to prevent it.

Everyone has a pair of genes that make the Mucolipin-1 protein. In children with Mucolipidosis IV, neither of these genes works correctly. These children inherit one non-working gene from each parent.

Parents of children with Mucolipidosis IV are carriers of the condition. Carriers do not have the disorder because the other gene of this pair is working correctly.

When both parents are carriers, in each pregnancy the risk to the baby is as follows:

  • 25% chance (1 in 4) of Mucolipidosis IV
  • 50% chance (1 in 2) for the baby to be a carrier of Mucolipidosis IV
  • 25% chance (1 in 4) for the baby to have two working genes and neither have Mucolipidosis IV or be a carrier

Relevant Organisations

References

References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing helen@metabolicsupportuk.org [Resource Library No: MLY038].

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