Major hyperpipecolataemia in a normal adult

Laboratory diagnosis of disorders of peroxisomal biogenesis and function: a technical standard of the American College of Medical Genetics and Genomics (ACMG)

Peroxisomal disorders are a clinically and genetically heterogeneous group of diseases caused by defects in peroxisomal biogenesis or function, usually impairing several metabolic pathways. Peroxisomal disorders are rare; however, the incidence may be underestimated due to the broad spectrum of clinical presentations. The inclusion of X-linked adrenoleukodystrophy to the Recommended Uniform Screening Panel for newborn screening programs in the United States may increase detection of this and other peroxisomal disorders. The current diagnostic approach relies heavily on biochemical genetic tests measuring peroxisomal metabolites, including very long-chain and branched-chain fatty acids in plasma and plasmalogens in red blood cells. Molecular testing can confirm biochemical findings and identify the specific genetic defect, usually utilizing a multiple-gene panel or exome/genome approach. When next-generation sequencing is used as a first-tier test, evaluation of peroxisome metabolism is often necessary to assess the significance of unknown variants and establish the extent of peroxisome dysfunction. This document provides a resource for laboratories developing and implementing clinical biochemical genetic testing for peroxisomal disorders, emphasizing technical considerations for sample collection, test performance, and result interpretation. Additionally, considerations on confirmatory molecular testing are discussed.

Zellweger spectrum disorders: clinical overview and management approach

Zellweger spectrum disorders (ZSDs) represent the major subgroup within the peroxisomal biogenesis disorders caused by defects in PEX genes. The Zellweger spectrum is a clinical and biochemical continuum which can roughly be divided into three clinical phenotypes. Patients can present in the neonatal period with severe symptoms or later in life during adolescence or adulthood with only minor features. A defect of functional peroxisomes results in several metabolic abnormalities, which in most cases can be detected in blood and urine. There is currently no curative therapy, but supportive care is available. This review focuses on the management of patients with a ZSD and provides recommendations for supportive therapeutic options for all those involved in the care for ZSD patients.

Peroxisome biogenesis disorders

Defects in PEX genes impair peroxisome assembly and multiple metabolic pathways confined to this organelle, thus providing the biochemical and molecular bases of the peroxisome biogenesis disorders (PBD). PBD are divided into two types--Zellweger syndrome spectrum (ZSS) and rhizomelic chondrodysplasia punctata (RCDP). Biochemical studies performed in blood and urine are used to screen for the PBD. DNA testing is possible for all of the disorders, but is more challenging for the ZSS since 12 PEX genes are known to be associated with this spectrum of PBD. In contrast, PBD-RCDP is associated with defects in the PEX7 gene alone. Studies of the cellular and molecular defects in PBD patients have contributed significantly to our understanding of the role of each PEX gene in peroxisome assembly.

Metabolic and molecular basis of peroxisomal disorders: a review

The group of peroxisomal disorders now includes 17 different disorders with Zellweger syndrome as prototype. Thanks to the explosion of new information about the functions and biogenesis of peroxisomes, the metabolic and molecular basis of most of the peroxisomal disorders has been resolved. A review of peroxisomal disorders is provided in this paper.

Hyperpipecolic acidaemia: a diagnostic tool for peroxisomal disorders

Peroxisomal disorders include a complex spectrum of diseases, characterized by a high heterogeneity from both the clinical and the biochemical points of view. Specific assays are required for the study of peroxisome metabolism. Among these, pipecolic acid evaluation is considered as a supplementary test. We have established the diagnostic role of pipecolic acid in 30 patients affected by a peroxisomal defect (5 Zellweger syndromes, 10 Infantile Refsum diseases, 1 neonatal adrenoleukodystrophy, 6 patients affected by a peroxisomal biogenesis disorder with unclassified phenotype, 1 case of rhizomelic chondrodysplasia punctata (RCDP), 2 acyl-CoA oxidase deficiencies, 2 bifunctional enzyme deficiencies, 2 Refsum diseases, and 1 beta-oxidation deficiency). Pipecolic acid was increased in all generalized peroxisomal disorders, while normal pipecolic acid with abnormal very long chain fatty acid concentrations was strong evidence for a single peroxisomal enzyme deficiency. Unexpectedly, hyperpipecolic acidaemia was found also in a child affected by RCDP and in two patients with Refsum disease. In six patients the suggestion of a peroxisomal disorder was raised by the fortuitous finding of a pipecolic acid peak in amino acid chromatography, routinely performed as a general metabolic screening. For all patients, pipecolic acid proved to be a useful parameter in the biochemical classification of peroxisomal disorders.