Very long-chain fatty acid determination is useful for the evaluation of patients with potential peroxisome aberrations, and gene disorders of peptide metabolism, such as X-linked adrenoleukodystrophy or peroxisome biogenesis disorders.
Very long-chain fatty acids (VLCFAs) are fatty acids with 22 or more carbons. Their biosynthesis takes place in the endoplasmic reticulum and represents only a small percentage of the total fatty acids content of a cell. Unlike most fatty acids, very-long-chain fatty acids are too large to be metabolized in mitochondria and must be metabolized to peroxisomes.
Peroxisomes are organelles that are present in all cells except mature erythrocytes. They are involved in basic metabolic functions, such as very long-chain beta-oxidation of fatty acids, alpha-oxidation of phytanic acid, and bile acid biosynthesis. Peroxisome disorders include disorders of their biogenesis by a defective assembly of the entire organelle as well as disorders of the enzymes and transport molecules in which the organelle is intact but disrupts a particular function. The beta-oxidation of VLCFA is affected in all disorders of peroxisome biogenesis and in some individual enzyme deficiencies, particularly in X-linked adrenoleukodystrophy (ALD), resulting in elevated serum VLCFA concentrations.
Peroxisomal biogenesis disorders include the spectrum disorders of Zellweger syndrome that range in severity from deadly Zellweger syndrome to neonatal adrenoleukodystrophy and Refsum disease. Affected children usually have lethargy, malnutrition, special facial features, seizures, and liver dysfunction. Other features may include retinal dystrophy, hearing loss, developmental delay, and bleeding episodes.
X-linked adrenoleukodystrophy (X-ALD) is a neurological disorder that affects the white matter and adrenal cortex. It can occur between the ages of 4 and 8 with behavioral and cognitive impairments (brain form). Other forms include Addison's disease phenotype with cortical adrenal insufficiency, without neurological abnormalities. Adrenal leukodystrophy is a condition associated with the X chromosome and affects mainly men. However, some girls who are carriers may develop neurological events later in their lives.
Refsum disease is a peroxisome disorder characterized by anosmia, pigmentary retinopathy, neuropathy, deafness, ataxia, ichthyosis, and cardiac abnormalities. The classic biochemical profile of Refsum's disease involves elevated plasma phytanic acid levels.
Biochemical abnormalities in peroxisomal disorders include the accumulation of very long-chain fatty acids, i.e. phytanic acid and pristanic acid. The differential diagnosis of these disorders is based on the recognition of the clinical picture in combination with specific biochemical tests to evaluate the peroxisome structure and function. Such tests include the measurement and specific ratios of VLCFAs (behenic, lignoceric, and hexacosanoic acid), phytanic acid, and pristanic acid.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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