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Phytanic Acid – Sources, Metabolism & Refsum Disease

Phytanic acid is a branched-chain fatty acid obtained through animal-based foods. When its breakdown is impaired, it can accumulate in the body and lead to serious metabolic disorders.

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Things worth knowing about "Phytanic Acid"

Phytanic acid is a branched-chain fatty acid obtained through animal-based foods. When its breakdown is impaired, it can accumulate in the body and lead to serious metabolic disorders.

What is Phytanic Acid?

Phytanic acid (German: Phytansäure) is a branched-chain saturated fatty acid with the chemical formula C₂₀H₄₀O₂. It belongs to the group of isoprenoid fatty acids and is derived primarily from the degradation of phytol, a component of chlorophyll found in plants. The human body cannot synthesize phytanic acid on its own; it enters the organism exclusively through dietary intake.

Dietary Sources and Absorption

Phytanic acid is found predominantly in foods of animal origin, as ruminants convert phytol from chlorophyll in their diet into phytanic acid. Major dietary sources include:

Dairy products (butter, cheese, whole milk)
Fatty meat from ruminants (beef, lamb)
Fatty fish (salmon, tuna, cod)
Liver and other organ meats

The average daily intake in adults is approximately 50–100 mg, though this can be substantially higher with a diet rich in animal fats.

Metabolism and Breakdown

In a healthy organism, phytanic acid is broken down within the peroxisomes of cells. Because its methyl branch at the alpha-carbon position prevents direct beta-oxidation, it must first undergo alpha-oxidation. This converts phytanic acid into pristanic acid, which can then be processed through regular beta-oxidation. This pathway requires several specific enzymes, most notably phytanoyl-CoA hydroxylase (PAHX), also known as PHYH.

Clinical Significance: Refsum Disease

When the breakdown of phytanic acid is disrupted due to a genetic enzyme defect, pathological accumulation of phytanic acid occurs in the blood and various tissues. This is the hallmark of the rare hereditary condition Refsum disease (also known as heredopathia atactica polyneuritiformis), an autosomal recessive disorder.

Symptoms of Refsum Disease

Retinitis pigmentosa (progressive retinal degeneration leading to visual impairment)
Peripheral polyneuropathy (numbness, tingling, and muscle weakness in the limbs)
Cerebellar ataxia (balance and coordination difficulties)
Anosmia (loss of smell)
Cardiomyopathy and cardiac arrhythmias
Ichthyosis (dry, scaly skin)
Skeletal and joint abnormalities

Diagnosis and Treatment of Refsum Disease

Diagnosis is made by measuring phytanic acid concentrations in blood serum, supported by molecular genetic testing. Normal serum levels are below 0.3 mg/dl; in Refsum disease, levels may be elevated many times above this threshold.

Treatment is primarily based on a phytanic acid-restricted diet, strictly limiting dairy products, fatty ruminant meat, and oily fish. In addition, plasmapheresis (plasma exchange) may be used to rapidly reduce phytanic acid levels, especially during acute metabolic crises.

Phytanic Acid and Other Peroxisomal Disorders

Elevated phytanic acid levels are also observed in other peroxisomal biogenesis disorders, such as Zellweger syndrome and neonatal adrenoleukodystrophy. In these conditions, overall peroxisomal function is compromised, leading to impaired phytanic acid catabolism alongside other metabolic defects.

Research and Current Developments

Ongoing research is investigating phytanic acid as a potential ligand for the retinoid X receptor (RXR) and peroxisome proliferator-activated receptor alpha (PPAR-alpha), suggesting a possible role in gene regulation and lipid metabolism. Furthermore, the relevance of phytanic acid levels in the context of other neurodegenerative diseases is an active area of scientific inquiry.

References

Wanders RJA, Komen JC, Ferdinandusse S. Phytanic acid metabolism in health and disease. Biochimica et Biophysica Acta, 2011; 1811(9): 498–507.
Steinberg D. Refsum disease. In: Scriver CR et al. (eds.): The Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill, 2001.
Kohlschütter A, Schaumburg HH. Phytanic acid storage disease (Refsum disease). In: Handbook of Clinical Neurology, 2013; 113: 1353–1356.

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