Clinical characteristics: Refsum disease is characterized by anosmia and early-onset retinitis pigmentosa, which are both universal findings with variable combinations of neuropathy, deafness, ataxia, and ichthyosis. Onset of symptoms ranges from age seven months to older than age 50 years. Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems that develop later in life.
Diagnosis/testing: The diagnosis of Refsum disease is suspected on the basis of clinical findings and a plasma phytanic acid concentration greater than 200 µmol/L in most affected individuals. Confirmation of the diagnosis requires either (1) molecular genetic testing to identify biallelic pathogenic variants in either PHYH (encoding phytanoyl-CoA hydroxylase), which accounts for more than 90% of Refsum disease, or PEX7 (encoding the PTS2 receptor), which accounts for less than 10% of Refsum disease; or (2) enzyme analysis to identify deficiency of either phytanoyl-CoA hydroxylase enzyme activity or the peroxisome-targeting signal type 2 receptor.
Management: Treatment of manifestations: Dietary restriction of phytanic acid intake helps resolve ichthyosis, sensory neuropathy, and ataxia. Supportive treatment includes hydrating creams for ichthyosis and drugs for cardiac arrhythmias and cardiomyopathy. Plasmapheresis or lipid apheresis is used for acute arrhythmias or extreme weakness. A high-calorie diet prevents mobilization of phytanic acid into the plasma. Agents/circumstances to avoid: Fasting and/or sudden weight loss; ibuprofen. Evaluation of relatives at risk: Testing of sibs of a proband ensures early treatment to reduce plasma phytanic acid concentration before symptoms occur.
Genetic counseling: Refsum disease is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives and prenatal diagnosis for pregnancies at increased risk are possible if the PEX7 or PHYH pathogenic variants have been identified in an affected family member.
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