Very long chain fatty acids (VLCFA), phytanic acid, pristanic acid plasma
Clinical Background:
The VLCFA (C22:0, C24:0 and C26:0), phytanic and pristanic acid are measured to aid diagnosis of an inherited peroxisomal disorder. This test assesses the ability of peroxisomes to carry out alpha...
The VLCFA (C22:0, C24:0 and C26:0), phytanic and pristanic acid are measured to aid diagnosis of an inherited peroxisomal disorder. This test assesses the ability of peroxisomes to carry out alpha oxidation (phytanic acid) and beta oxidation (VLCFA and pristanic acid) of fatty acids.
There are 2 types of peroxisomal disorder: peroxisomal biogenesis disorders (PBDs) and single enzyme or transporter defects.
PBDs
These comprise Zelweger spectrum disorders (ZSDs) and rhizomelic chondrodysplasia punctata (RCDP) Types I and V. The ZSDs include Zellweger Syndrome, neonatal adrenoleukodystrophy and infantile Refsum disease. See ‘indications for requesting the test’ below for classical clinical features of these conditions.
Plasmalogens is another test of peroxisomal function that is expected to show abnormally low results in patients with any of the RCDP types. Therefore this test should be requested if any of the RCDP types are suspected (see separate entry for information on this test).
Single enzyme or transporter defects
Several peroxisomal single enzyme or tranporter defects may be detected with this test:
· X-linked adrenoleukodystrophy (X-ALD)
· Acyl CoA oxidase 1 (ACOX-1) deficiency
· ACBD5 deficiency
· D bifunctional protein (DBP) deficiency
· Sterol carrier protein (SCPx) deficiency
· 2-methyl acyl CoA racemase (AMACR) deficiency
· Refsum disease
Other peroxisomal single enzyme or tranporter defects will not show abnormalities of VLCFA, pristanic or phytanic acids:
· RCDP types 2, 3 & 4: low plasmalogens is the only peroxisomal marker expected to be abnormal
· Acyl CoA oxidase 2 (ACOX-2) and PMP70 deficiencies: abnormalities expected in urine bile acids profile
· Bile acid-CoA: amino acid N-acyltransferase (BAAT) deficiency
Indications for requesting the test
· Classical features of a Zellweger Spectrum Disorder (ZSD): characteristic facial dysmorphism, profound neurological abnormalities
· Classical features of a Rhizomelic Chondrodysplasia Punctata (RCDP): shortening of bones in upper arms and thighs, stippled calcification in epiphyseal cartilage, cataracts, characteristic facial abnormalities
· Unexplained hypotonia, dysmorphism or seizures in a neonate
· In older children: retinitis pigmentosa, sensory neural deafness, liver dysfunction, dysmorphism, psychomotor retardation
· In adults: ataxia, cerebellar syndrome, neuropathy, retinitis pigmentosa
Test Details
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Discipline:
Biochemistry
Biochemistry
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Specimen Container Adult:
EDTA plasma
EDTA plasma
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Specimen Container Paediatric:
EDTA plasma
EDTA plasma
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Minimum Volume Adult:
1 mL blood
1 mL blood
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Minimum Volume Paediatric:
1 mL blood
1 mL blood
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Special Requirement:
A fasting blood sample is recommended.
A fasting blood sample is recommended.
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Interpretation:
Neonates
It is important to note that detecting increased phytanic and pristanic acids in affected patients is dependent on dietary phytanic acid intake and so these abnormalities may not be presen...
Read MoreNeonates
It is important to note that detecting increased phytanic and pristanic acids in affected patients is dependent on dietary phytanic acid intake and so these abnormalities may not be present in affected neonates.
Expected results in Peroxisomal biogenesis disorders (PBDs)
In ZSDs increased C26:0 and C24:0/C22:0 ratio are expected. Pristanic acid and phytanic acid may also be increased (dependent on diet, see above). VLCFA are expected to be normal in RCDP types I and V, with an increase in phytanic acid (dependent on diet, see above).
Plasmalogens is another test of peroxisomal function that is expected to show abnormally low results in patients with any of the RCDP types. Therefore this test should be requested if any of the RCDP types are suspected (see separate entry for information on this test).
Expected results in single enzyme and transporter disorders
· X-linked adrenoleukodystrophy (X-ALD): increased C26:0 and C24:0/C22:0 ratio
· Acyl CoA oxidase 1 (ACOX-1) deficiency: increased C26:0 and C24:0/C22:0 ratio
· ACBD5 deficiency: increased C26:0 and C24:0/C22:0 ratio
· D bifunctional protein (DBP) deficiency: increased C26:0, C24:0/C22:0 ratio. Phytanic and pristanic acids normal or increased (dependent on diet, see above). Pristanic acid > phytanic acid
· Sterol carrier protein (SCPx) deficiency: phytanic and pristanic acids normal or increased (dependent on diet, see above). Pristanic acid > phytanic acid.
· 2-methyl acyl CoA racemase (AMACR) deficiency: phytanic and pristanic acids normal or increased (dependent on diet, see above). Pristanic acid > phytanic acid.
· Refsum disease: increased phytanic acid.
About 20% of female X-ALD carriers have been reported to have normal VLCFAs values. Lack of elevation of C26:0 and of the C24:0/C22:0 ratio may therefore not completely exclude X-ALD carrier status. Results from females within reference ranges are reported with this caveat.
Other causes of abnormal results
Dyslipidaemia may be associated with increased C26:0 and C26:0/C22:0 ratio. Pristanic and phytanic acids may also be raised.
Consumption of peanuts within last 12 hr can cause C26:0 and C26:0/C22:0 ratio to be increased.
Additional investigations
Measurement of red cell plasmalogens or bile acid metabolites in urine or plasma is required for investigation of some of the inherited peroxisomal disorders (see above). Details of these investigations can be found separately on the website.
Molecular genetic testing is required to confirm the diagnosis of an inherited peroxisomal disorder. Contact the genetics laboratory for details.
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Reference Ranges:
C22:0 fatty acid
38.0 - 90.5 µmol/L
C24:0 fatty acid
33.1 - 75.0 µmol/L
C26:0 fatty acid
0.30 - 1.49 µmol/L
C24:0 / C22:0 ratio
0.35 - 1.10
C26:0 / C22:0 ratio
0....
Read MoreC22:0 fatty acid
38.0 - 90.5 µmol/L
C24:0 fatty acid
33.1 - 75.0 µmol/L
C26:0 fatty acid
0.30 - 1.49 µmol/L
C24:0 / C22:0 ratio
0.35 - 1.10
C26:0 / C22:0 ratio
0.003 - 0.03
Phytanic acid
0.3 - 11.5 µmol/L
Pristanic acid
0.0 - 1.5 µmol/L
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Other Info:
Lithium heparin plasma and serum samples are also acceptable.
Lithium heparin plasma and serum samples are also acceptable.
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Routine Contact Name:
Duty biochemist
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Routine Telephone:
Freeman: 0191 244 8889
RVI: 0191 282 9719
Freeman: 0191 244 8889
RVI: 0191 282 9719
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Routine Email:
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Specialist Test:
Yes
Yes
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Specialist Contact Name:
Metabolic Clinical Scientist
Metabolic Clinical Scientist
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Specialist Telephone:
0191 282 9685 (Consultant Clinical Scientist)
0191 282 0334 (Metabolic Laboratory)
0191 282 9685 (Consultant Clinical Scientist)
0191 282 0334 (Metabolic Laboratory)
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Specialist Email: