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Test ID: POX
Fatty Acid Profile, Peroxisomal (C22-C26), Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Evaluating patients with possible peroxisomal disorders, including X-linked adrenoleukodystrophy and Refsum disease

 

Aid in the assessment of peroxisomal function

Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request

Reports include concentrations of C22:0, C24:0, C26:0 species, phytanic acid and pristanic acid, and calculated C24:0/C22:0, C26:0/C22:0, and phytanic acid/pristanic acid ratios.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Peroxisomes are organelles present in all human cells except mature erythrocytes. They carry out essential metabolic functions including beta-oxidation of very long-chain fatty acids (VLCFA), alpha-oxidation of phytanic acid, and biosynthesis of plasmalogen and bile acids. Peroxisomal disorders include 2 major subgroups: disorders of peroxisomal biogenesis and single peroxisomal enzyme/transporter defects. Peroxisome biogenesis defects such as Zellweger syndrome, are characterized by defective assembly of the entire organelle, whereas in single enzyme/transporter defects such as Refsum disease and X-linked adrenoleukodystrophy, the organelle is intact, but a specific function is disrupted. These disorders are clinically diverse and range in severity from neonatal lethal to later onset milder variants.

               

Biochemical abnormalities include accumulations of VLCFA, phytanic and pristanic acid. The differential diagnosis of these disorders is based on recognition of clinical phenotypes combined with a series of biochemical tests to assess peroxisomal function and structure. These include measurements of VLCFA, pipecolic acid (PIPA/81326 Pipecolic Acid, Serum; PIPU/81248 Pipecolic Acid, Urine), phytanic acid and its metabolite pristanic acid.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

C22:0

< or =96.3 nmol/mL

 

C24:0

< or =91.4 nmol/mL

 

C26:0

< or =1.30 nmol/mL

 

C24:0/C22:0 RATIO

< or =1.39

 

C26:0/C22:0 RATIO

< or =0.023

 

PRISTANIC ACID

0-4 months: < or =0.60 nmol/mL

5-8 months: < or =0.84 nmol/mL

9-12 months: < or =0.77 nmol/mL

13-23 months: < or =1.47 nmol/mL

> or =24 months: < or =2.98 nmol/mL

 

PHYTANIC ACID

0-4 months: < or =5.28 nmol/mL

5-8 months: < or =5.70 nmol/mL

9-12 months: < or =4.40 nmol/mL

13-23 months: < or =8.62 nmol/mL

> or =24 months: < or =9.88 nmol/mL

 

PRISTANIC/PHYTANIC ACID RATIO

0-4 months: < or =0.35

5-8 months: < or =0.28

9-12 months: < or =0.23

13-23 months: < or =0.24

> or =24 months: < or =0.39

Interpretation Provides information to assist in interpretation of the test results

Reports include concentrations of C22:0, C24:0, C26:0 species, phytanic acid and pristanic acid, and calculated C24:0/C22:0, C26:0/C22:0, and phytanic acid/pristanic acid ratios. When no significant abnormalities are detected, a simple descriptive interpretation is provided.

 

A profile of elevated phytanic acid, low-normal pristanic acid, and normal very long-chain fatty acids (VLCFA) is suggestive of Refsum disease (phytanic acid oxidase deficiency); however, serum phytanic acid concentration may also be increased in disorders of peroxisomal biogenesis and should be considered in the differential diagnosis of peroxisomal disorders.

 

If results are suggestive of hemizygosity for X-linked adrenoleukodystrophy (X-ALD), we also include the calculated value of a discriminating function used to more accurately segregate hemizygous individuals from normal controls.

 

When a diagnosis of X-ALD (hemizygous male) or heterozygosity for X-ALD is suspected, the report suggests contacting the coordinator of a multicenter study.

 

Positive test result could be due to genetic or non-genetic condition. Additional confirmatory testing would be required.

 

When abnormal results are detected, a detailed interpretation is provided including an overview of the results and of their significance, a correlation to available clinical information, elements of differential diagnosis (including the calculation of a discriminating function[1]), recommendations for additional biochemical testing and in vitro confirmatory studies (enzyme assay, molecular analysis), name and phone number of key contacts who may provide these studies at Mayo or elsewhere, and a phone number to reach one of the laboratory directors in case the referring physician has additional questions.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

In rare instances, patients with X-linked adrenoleukodystrophy (X-ALD) may have only minimally elevated values; 15% to 20% of women heterozygous for X-ALD have normal plasma very long-chain fatty acid levels.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Moser AB, Kreiter N, Bezman L, et al: Plasma very long chain fatty acid assay in 3,000 peroxisome disease patients and 29,000 controls. Ann Neurol 1999;45:100-110

2. Wanders RJA: Inborn Errors of Peroxisome Biogenesis and Function. In Pediatric Endocrinology and Inborn Errors of Metabolism. Edited by K Sarafoglou, GF Hoffmann, KS Roth, New York, NY, McGraw-Hill Medical Division, 2009, pp 323-337