What else is it called?
- Adult Refsum disease
- Classic Refsum disease
- Hereditary motor and sensory neuropathy Type IV
- Heredopathia atactica polyneuritiformis
- HMSN IV
- HMSN type IV
- Phytanic acid storage disease
- Refsum syndrome
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What causes it?
More than 90 percent of all cases of Refsum disease result from mutations in the PHYH gene. The remaining cases are caused by mutations in a gene called PEX7. The signs and symptoms of Refsum disease result from the abnormal build-up of a type of fatty acid called phytanic acid. This substance is obtained from the diet, particularly from beef and dairy products. It is normally broken down through a process called alpha-oxidation, which occurs in cell structures called peroxisomes. These sac-like compartments contain enzymes that process many different substances, such as fatty acids and certain toxic compounds.
Mutations in either the PHYH or PEX7 gene disrupt the usual functions of peroxisomes, including the breakdown of phytanic acid and therefore a build-up of these substances in the tissues of your child’s body.
How common is it?
Due to the rarity of this condition there is no current evidence of how many people have been diagnosed with this condition.
What are the signs and symptoms?
The age of onset of Refsum disease can vary. This may occur at any given time from early childhood until around 50 years of age, but most symptoms will have appeared by age 20. Males and females are affected in equal numbers. Vision loss and anosmia [absence of smell] are seen in almost everyone with Refsum disease, but other signs and symptoms vary such as:
- Poor balance and coordination [Ataxia]
- degenerative nerve disease
- Hearing loss
- Dry, scaly skin
- Abnormal heart rhythm
- Peripheral neuropathy
- Elevated protein levels in the cerebrospinal fluid
How is it diagnosed?
Diagnosis is usually made with the presence of phytanic acid in blood or urine samples is diagnostic alongside the presentations of symptoms for this condition.
Can it be treated?
Treatment of Refsum disease involves following a strict diet low in phytanic acid (found in dairy products, beef, lamb and some seafoods) and high in calories. The removal and reinfusion of blood plasma (plasmapheresis) may also be required. Other treatment is symptomatic and supportive.
Do my family need to be tested?
Refsum disease 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 Refsum disease. 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.
If you have previously had a child with Refsum disease and go on to have further children, their New-born Screening test should be carried out within 24-48 hours of birth.