Peroxisomes are intracellular organelles that contain enzymes for beta-oxidation. These enzymes overlap in function with those in mitochondria, with the exception that mitochondria lack enzymes to metabolize very long-chain fatty acids (VLCFA), those 20 to 26 carbons in length. Therefore, peroxisomal disorders generally manifest with elevated VLCFA levels (except rhizomelic chondrodysplasia and Refsum disease). Although VLCFA levels may help screen for these disorders, other assays are also required (eg, plasma levels of phytanic, pristanic, and pipecolic acids; red blood cell plasmalogen levels). For information on other disorders affecting fatty acid metabolism, see Overview of Fatty acid and Glycerol Metabolism Disorders. See also Approach to the Patient With a Suspected Inherited Disorder of Metabolism and testing for suspected inherited disorders of metabolism.
There are 2 types of peroxisomal disorders:
X-linked adrenoleukodystrophy is the most common peroxisomal disorder (incidence 1/17,000 births); all others are autosomal recessive, with a combined incidence of about 1/50,000 births.
For more information, see the table.
Peroxisome Biogenesis and Very Long-Chain Fatty Acid Metabolism Disorders
Disease (OMIM Number) |
Defective Proteins or Enzymes |
Comments |
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Cerebrohepatorenal syndrome (Zellweger syndrome; 214100*) |
Peroxin-1 |
Biochemical profile: Decreased dihydroxyacetone phosphate acyltransferase and plasmalogen; elevated very long-chain fatty acids, phytanic acid, pipecolate, iron, and total iron-binding capacity Clinical features: Growth failure, large fontanelles, macrocephaly, turribrachycephaly, dysmorphic facies, cataracts, nystagmus, congenital heart disease, hepatomegaly, biliary dysgenesis, hypospadias, renal cysts, hypotonia, brain malformation Treatment: Symptomatic, no specific treatment, although cholic acid is being evaluated |
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Peroxin-2 |
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Peroxin-3 |
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Peroxin-5 |
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Peroxin-6 |
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Peroxin-12 |
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Peroxin-14 |
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Peroxin-26 |
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Neonatal adrenoleukodystrophy (202370*) |
Peroxin-1 |
Biochemical profile: Elevated very long-chain fatty acids Clinical features: Dolichocephaly, dysmorphic facies, cataracts, hyperpigmentation, seizures, developmental delay, adrenal insufficiency Treatment: Symptomatic, no specific treatment |
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Peroxin-5 |
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Peroxin-10 |
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Peroxin-13 |
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Peroxin-26 |
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Infantile Refsum disease (266510*) |
Peroxin-1 |
Biochemical profile: Elevated plasma phytanic acid, cholesterol, very long-chain fatty acids, dihydroxycholestanoic acid, trihydroxycholestanoic acid, and pipecolic acid Clinical features: Growth and developmental delay, peripheral neuropathy, hypotonia, deafness, facial dysmorphism, retinopathy, osteoporosis, steatorrhea, episodic bleeding, hepatomegaly Treatment: Symptomatic, no specific treatment |
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Peroxin-2 |
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Peroxin-26 |
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Biochemical profile: In type 1, plasmalogen deficiency, elevated plasma phytanic acid and unprocessed 3-oxoacyl CoA thiolase, acyl-CoA dihydroxyacetonephosphate acyltransferase deficiency In type 2, normal plasmalogen, phytanic acid, alkyl dihydroxyacetonephosphate synthase, and peroxisomal thiolase; dihydroacetonephosphate acyltransferase deficiency In type 3, abnormal peroxisomes, alkyl dihydroxyacetonephosphate synthase deficiency Clinical features: Dwarfism with rhizomelic limb shortening, punctuate epiphyseal calcification, and metaphyseal splaying; severe growth and developmental delay; microcephaly; midface hypoplasia; micrognathia; sensorineural deafness; cataracts; cleft palate; ichthyosis; respiratory difficulties; kyphoscoliosis; vertebral clefts; spasticity; cortical atrophy; seizures; death before 2 years Treatment: Symptomatic, no specific treatment |
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Type 1 (215100*) |
Peroxin-7 |
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Type 2 (222765*) |
Dihydroxyacetonephosphate acyltransferase |
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Type 3 (600121*) |
Alkyldihydroxyacetonephosphate synthase |
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Hyperpipecolicacidemia (239400*) |
Pipecolate oxidase |
Biochemical profile: Elevated plasma pipecolate, mild generalized aminoaciduria Clinical features: Hepatomegaly, demyelination, central nervous system degeneration, severe intellectual disability and developmental delay, retinopathy Treatment: Symptomatic, no specific treatment |
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X-linked adrenoleukodystrophy (300100*) |
ATP-binding cassette transporter 1 |
Biochemical profile: Elevated plasma very long-chain fatty acids, peroxisomal lignoceroyl-CoA ligase deficiency Clinical features: Hyperpigmentation, blindness, cognitive hearing loss, spastic paraplegia, impotence, sphincter disturbance, ataxia, dysarthria, adrenal insufficiency, hypogonadism, pontine and cerebellar atrophy Treatment: Adrenal hormone replacement, bone marrow transplantation 4:1 mixture of glyceryl trioleate and glycerol trierucate (Lorenzo’s oil) apparently of no clinical benefit once the disease manifests but may slow progression if used prior to symptom onset Some success in current gene therapy trials |
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Acyl-CoA oxidase 1 deficiency (pseudoneonatal adrenoleukodystrophy; 264470*) |
Straight-chain peroxisomal acyl-CoA oxidase |
Biochemical profile: Elevated plasma very long-chain fatty acids; normal peroxisomal phytanate, pipecolate, dihydroxycholestanoic acid, and trihydroxycholestanoic acid Clinical features: Neonatal hypotonia, developmental delay, sensorineural deafness, retinopathy, no dysmorphic features, leukodystrophy at age 2 to 3 years Treatment: Not established |
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D-Bifunctional protein deficiency (261515*) |
D-bifunctional enzyme |
Biochemical profile: Elevated serum very long-chain fatty acids and pipecolate, elevated trihydroxycholestanoic acid in duodenal aspirate, peroxisomal 3-oxoacyl-CoA thiolase defect Clinical features: Hypotonia, exaggerated startle reflex, facial diplegia, seizures, high-pitched and weak cry, developmental delay, myopathic facies, high-arched palate, abducted limbs, ventricular heart disease Treatment: Not established |
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2-Methylacyl-CoA racemase deficiency |
2-Methylacyl-CoA racemase |
Biochemical profile: Elevated plasma pristanic acid Clinical features: Adult-onset sensorimotor neuropathy, retinopathy Treatment: Not established |
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Primary oxaluria |
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Biochemical profile: Elevated urinary oxalate excretion, glycolic aciduria Clinical features: Calcium oxalate urolithiasis, nephrocalcinosis, renal failure, heart block, peripheral vascular insufficiency, arterial occlusion, intermittent claudication, optic neuropathy, fractures, death during childhood or early adulthood Type 2 milder than type 1 Treatment: Hepatorenal transplantation |
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Hyperoxaluria type 1 (259900*) |
Peroxisomal alanine-glyoxylate aminotransferase |
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Hyperoxaluria type 2 (260000*) |
D-Glycerate dehydrogenase glyoxylate reductase |
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Refsum disease (266500*) |
Phytanoyl-CoA hydroxylase |
Biochemical profile: Elevated plasma and tissue phytanic acid Clinical features: Retinitis pigmentosa, ataxia, ptosis, miosis, peripheral neuropathy, anosmia, heart failure, deafness, ichthyosis, short 4th metacarpal Treatment: Low phytanic acid diet, plasmapheresis |
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Peorxin-7 |
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Glutaric aciduria type 3 (231690*) |
Peroxisomal glutaryl CoA oxidase |
Biochemical profile: Glutaric aciduria exacerbated by lysine loading Clinical features: Failure to thrive, postprandial vomiting Treatment: Not established, possible benefit from riboflavin |
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Mevalonic aciduria |
— |
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Acatalasemia (115500*) |
Catalase |
Biochemical profile: Failure of tissue to cause hydrogen peroxide frothing Clinical features: Ulcerating oral lesions in Japanese patients but not in Swiss patients Treatment: Symptomatic, no specific treatment |
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* For complete gene, molecular, and chromosomal location information, see the Online Mendelian Inheritance in Man® (OMIM®) database. |
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Zellweger syndrome (ZS), neonatal adrenoleukodystrophy, and infantile Refsum disease (IRD)
These disorders are 3 expressions of a disease continuum, from most (ZS) to least (IRD) severe. The responsible genetic defect occurs in 1 of at least 11 genes involved in peroxisomal formation or protein import (the PEX gene family).
Manifestations include facial dysmorphism, central nervous system malformations, demyelination, neonatal seizures, hypotonia, hepatomegaly, cystic kidneys, short limbs with stippled epiphyses (chondrodysplasia punctata), cataracts, retinopathy, hearing deficit, psychomotor delay, and peripheral neuropathy.
Diagnosis is by detecting elevated blood levels of VLCFA, phytanic acid, bile acid intermediates, and pipecolic acid.
There is currently no specific treatment for these disorders. Management is mainly symptomatic.
Rhizomelic chondrodysplasia punctata
This defect of peroxisomal biogenesis is caused by PEX7 gene mutations and characterized by skeletal changes that include midface hypoplasia, strikingly short proximal limbs, frontal bossing, small nares, cataracts, ichthyosis, and profound psychomotor retardation. Vertebral clefts are also common.
Diagnosis of rhizomelic chondrodysplasia punctata is suspected by x-ray findings, elevation of serum phytanic acid, and low red blood cell plasmalogen levels; VLCFA levels are normal. Confirmation is by genetic testing.
There is no specific treatment for rhizomelic chondrodysplasia punctata.
X-linked adrenoleukodystrophy
This disorder is caused by deficiency of the peroxisomal membrane transporter ALDP, which is coded for by the gene ABCD1. This is an X-linked gene and thus the disorder manifests primarily in males. Currently, > 800 mutations have been identified (see ALD Info).
The cerebral form affects 40% of patients. Onset occurs between age 4 years and 8 years, and symptoms of attention deficit progress over time to severe behavioral problems, dementia, and vision, hearing, and motor deficits, causing total disability and death 2 to 3 years after diagnosis. Milder adolescent and adult forms have also been described.
About 45% of patients have a milder form called adrenomyeloneuropathy (AMN); onset occurs in the 20s or 30s, with progressive paraparesis, and sphincter and sexual disturbance. About one third of these patients also develop cerebral symptoms.
Patients with any form may also develop adrenal insufficiency; about 15% have isolated Addison disease without neurologic involvement.
Diagnosis of X-linked adrenoleukodystrophy is suspected by isolated elevation of VLCFA and confirmed by gene sequencing.
Bone marrow or stem cell transplantation may help stabilize symptoms in some cases. Adrenal steroid replacement is needed for patients with adrenal insufficiency. Dietary supplement with a 4:1 mixture of glyceryl trioleate and glyceryl trierucate (Lorenzo’s oil) can normalize plasma VLCFA levels but does not appear to stop neurologic degeneration in symptomatic patients. However, if given to boys before symptom onset, it may slow disease progression; the exact benefit has not been determined. Gene therapy trials are currently underway and have shown some preliminary success.
Classic Refsum disease
Genetic deficiency of a single peroxisomal enzyme, phytanoyl-CoA hydroxylase, which catalyzes metabolism of phytanic acid (a common dietary plant component), causes phytanic acid accumulation.
Clinical manifestations include progressive peripheral neuropathy, impaired vision caused by retinitis pigmentosa, hearing deficit, anosmia, cardiomyopathy and conduction defects, and ichthyosis. Onset is usually in the 20s.
Diagnosis of Refsum disease is confirmed by elevation of serum phytanic acid and decreased levels of pristanic acid (phytanic acid elevation is accompanied by pristanic acid elevation in several other peroxisomal disorders).
Treatment of Refsum disease is dietary restriction of phytanic acid (< 10 mg/day), which can be effective in preventing or delaying symptoms when started before symptom onset.
More Information
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ALD Info (adrenoleukodystrophy)
