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Single-Enzyme Deficiencies

There are at least 10 different disorders in which there is a deficiency of a single peroxisomal enzyme but the structure of the peroxisome is intact.  They fall under these catagories: peroxisomal beta-oxidation disorders, disorders of ether-phospholipid biosynthesis, and disorders of fatty-acid alpha-oxidation.

Peroxisomal Beta-oxidation Disorders

X-ALD (X-linked Adrenoleukodystrophy): In the cerebral form, signs show up at 4-8 years of age and only in males.  This disorder involves the build-up of VLCFA due to the lack of peroxisomal oxidation. 

Acyl-CoA oxidase deficiency, or pseudo-NALD: Clinically, this disorder appears like NALD, but without dysmorphic features.  However, all peroxisomal metabolites are normal with the exception of VLCFA (very-long-chain fatty acids).

D-Bifunctional protein deficiency: This disorder results in a phenotype similar to that of Zellweger Syndrome, with dysmorphic facies and cerebral migrational defects. Levels of both VLCFA and bile-acid intermediates are abnormally elevated. However, peroxisomes appear normal on liver biopsy.

Peroxisomal thiolase deficiency, or pseudo-Zellweger Syndrome: This disorder is believed to be a subgroup of D-bifunctional protein deficiency, with a similar clinical appearance to Zellweger syndrome.

Peroxisomal 2-methylacyl-CoA racemase deficiency (AMACR):  This disorder is characterized by a defect in beta-oxidation of branched-chain fatty acids. Symtoms consist of adult-onset sensory-motor neuropathy, a symptom also reported in Refsum disease and in the ALD variant. However, phytanic acid and VLCFA levels are normal, though levels of 2-methyl branched-chain fatty acid, pristanic acid, and DHCA and/or THCA are abnormally elevated. Symptoms may vary, and patients may have isolated liver disease without neurologic involvement.

Disorders of Ether-phospholipid Biosynthesis

Rhizomelic chondrodysplasia punctata (RCDP) types II and III:  This disorder is similar to that of RCDP type I, however, bone stippling is not present.  In RCDP types II and III plasmalogen is deficient but, unlike RCDP type I, phytanic acid and other peroxisomal metabolites are normal.

Other disorders of Ether-phospholipid biosynthesis include: glutaric aciduria type III, Mevalonate kinase,

Acatalasemia, Mulibrey nanism, hyperoxaluria type I.

Disorders of Fatty-acid Alpha-oxidation

Refsum disease is the only known type in this group. It is characterized by sight problems, sensory-motor polyneuropathy, cerebellar ataxia, and elevated CSF protein levels without pleocytosis. Inconsistant features include sensory-neural hearing loss, anosmia, ichthyosis, skeletal malformation and cardiac abnormalities. No cognitive decline or dysmorphism is associated with this condition. Symptoms begin in adolescence. Accumulation of phytanic acid is the only known abnormality. The causative gene has been identified.

Information taken from the National Institute of Health's GeneReview site and an article by Aziza K Chedrawi, MD, Texas Children's Hospital.

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Last updated: June 1, 2007