Desmosterolosis

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This disorder is caused by a problem in the gene DHCR24. This gene provides instructions for the production of an enzyme called 24-dehydrocholesterol reductase which takes a role in the production of cholesterol. Our body can get cholesterol from animal foods (egg yolks, meat, poultry, fish, and dairy products) or produce its own where animal cholesterol cannot be accessed. This is the case with the brain, whose normal function is dependent on its own production of cholesterol.

If you have a problem in the DHCR24 gene, you will produce 24-dehydrocholesterol reductase with reduced activity. Therefore, it will severely impact the production of cholesterol in the brain, and this causes the death of brain cells. The most adverse consequences of reduced cholesterol production appear before birth rather than during other periods of development. Neurological problems appear as a result of such disruption.

We do not know how many people have this disorder. It is very rare with only a small amount of cases that are known. Due to its rarity, it is also unknown whether it affects more males or females or any specific ethnicity group.

Desmosterolosis is a progressive disorder with the onset of signs and symptoms during pregnancy or later during early infancy.

Signs and symptoms may include:

• Brain abnormalities

o Malformation of the tissue that connects the left and right halves of the brain (the corpus callosum)

o Loss of white matter, which consists of nerve fibers covered by a fatty substance called myelin

• Developmental delay

o Delayed speech and motor skills (such as sitting and walking)

o Verbal communication is often limited to a few words or phrases

• Muscle stiffness (spasticity)
• Stiff, rigid joints (arthrogryposis) affecting their hands and feet
• Short stature
• Abnormal head size (either larger or smaller than normal)
• Small lower jaw (micrognathia)
• Opening in the roof of the mouth (cleft palate)
• Involuntary eye movements (nystagmus)
• Eyes that do not look in the same direction (strabismus)
• Heart defects
• Seizures
• Uvula separated into two parts most easily seen at the tip (bifid uvula)
• Failure to thrive
• Feeding difficulties
• Weak jaw (retrognathia)
• Abnormality of the nose
• Abnormality of ears
• Sensorineural hearing loss
• Club foot
• Ambiguous genitalia
• Optic atrophy
• Renal problems
• Increased spleen size (splenomegaly)
• Abnormally increased formation of dense trabecular bone tissue (Osteopetrosis)
• The presence of abnormally small extremities (Micromelia)

You will be diagnosed after a clinical examination by your specialist or doctor. However, as the signs and symptoms of this disorder are similar to other conditions, you will need further tests. Doctors will analyse your blood using a special test. You may be required to undertake an MRI scan. The diagnosis is confirmed by DNA test.

Unfortunately, there is no curative treatment for this disease. Therefore, treatment is focused on managing individual symptoms and providing comfort and relief in the form of supporting the individual and any family members. A multi-disciplinary team of specialists and support networks will be involved in the management of the condition and to offer practical and emotional support.

The supplementation by anticholesterolemic and antiestrogenic drugs such as clomifene, ethamoxytriphetol, and triparanol have shown some potential in supportive treatment.

Desmosterolosis can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.

If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.

If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.

Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inherited Desmosterolosis. They can also tell you about genetic testing for the rest of your family. They can provide advice and support if you go on to have children of your own.

References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing contact@metabolicsupportuk.org [Resource Library No: AAP002].