Laboratory Diagnosis of Peroxisomal Disorders in the -Omics Era and the Continued Importance of Biomarkers and Biochemical Studies

Abstract The clinical as well as biochemical and genetic spectrum of peroxisomal diseases has markedly increased over the last few years, thanks to the revolutionary advances in the field of genome analysis and several -omics technologies. This has led to the recognition of novel disease phenotypes linked to mutations in previously identified peroxisomal genes as well as several hitherto unidentified peroxisomal disorders. Correct interpretation of the wealth of data especially coming from genome analysis requires functional studies at the level of metabolites (peroxisomal metabolite biomarkers), enzymes, and the metabolic pathway(s) involved. This strategy is not only required to identify the true defect in each individual patient but also to determine the extent of the deficiency as described in detail in this article.

Rosuvastatin lowers coenzyme Q10 levels, but not mitochondrial adenosine triphosphate synthesis, in children with familial hypercholesterolemia.

OBJECTIVE: To investigate whether statin therapy affects coenzyme Q10 (CoQ10) status in children with heterozygous familial hypercholesterolemia (FH). STUDY DESIGN: Samples were obtained at baseline (treatment naïve) and after dose titration with rosuvastatin, aiming for a low-density lipoprotein cholesterol level of 110 mg/dL. Twenty-nine patients were treated with 5, 10, or 20 mg of rosuvastatin for a mean period of 29 weeks. RESULTS: We found a significant (32%) decrease in peripheral blood mononuclear cell (PBMC) CoQ10 level (P = .02), but no change in PBMC adenosine triphosphate synthesis (P = .60). Uncorrected plasma CoQ10 values were decreased significantly, by 45% (P < .01). In contrast, ratios of plasma CoQ10/total cholesterol and CoQ10/low-density lipoprotein cholesterol remained equal during treatment. CONCLUSIONS: In children with FH, rosuvastatin causes a significant decrease in cellular PBMC CoQ10 status but does not affect mitochondrial adenosine triphosphate synthesis in children with FH. Further studies should address whether (rare) side effects of statin therapy could be explained by a deterioration in CoQ10 status.

Fasting and fat-loading tests provide pathophysiological insight into short-chain acyl-coenzyme a dehydrogenase deficiency.

OBJECTIVE: To gain insight into the pathophysiological and clinical consequences of short-chain acyl-coenzyme A dehydrogenase deficiency (SCADD). STUDY DESIGN: A retrospective study of 15 fasting and 6 fat-loading tests in 15 Dutch patients with SCADD, divided into 3 genotype groups. Metabolic and endocrinologic measurements and the biochemical characteristics of SCADD, ethylmalonic acid (EMA), and C4-carnitine were studied. RESULTS: Three patients had development of hypoglycemia during fasting; all of these had originally presented with hypoglycemia. Metabolic and endocrinologic measurements remained normal during all tests. The EMA excretion increased in response to fasting and fat loading, and plasma C4-carnitine remained stable. Test results did not differ between the 3 genotype groups. CONCLUSIONS: The metabolic profiles of the 3 patients with development of hypoglycemia resemble idiopathic ketotic hypoglycemia. Because hypoglycemia generally requires a metabolic work-up and because SCADD is relatively prevalent, SCADD may well be diagnosed coincidently, thus being causally unrelated to the hypoglycemia. If SCADD has any other pathologic consequences, the accumulation of potentially toxic metabolites such as EMA is most likely involved. However, the results of our study indicate that there is no clear pathophysiological significance, irrespective of genotype, supporting the claim that SCADD is not suited for inclusion in newborn screening programs.

Pitfalls of neonatal screening for very-long-chain acyl-CoA dehydrogenase deficiency using tandem mass spectrometry.

Neonatal screening programs for very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD) have recently been implemented. We report 2 newborns with elevated C14:1-carnitine levels on day 3 of life and normal levels on days 5 to 7. Enzyme and molecular analyses confirmed VLCADD in the first patient and heterozygosity in the second patient. We conclude that the diagnosis of VLCADD can be missed by acylcarnitine analysis during anabolic conditions. An increased C14:1-carnitine level can also occur in heterozygous individuals. Elevated C14:1-carnitine level on neonatal screening warrants further diagnostic workup even if a repeat sample demonstrates normal acylcarnitine levels.

Mitochondrial trifunctional protein deficiency: a severe fatty acid oxidation disorder with cardiac and neurologic involvement.

OBJECTIVE: To determine the spectrum of presentation, including both clinical and biochemical abnormalities, and the clinical course in a cohort of patients with complete mitochondrial trifunctional protein (MTP) deficiency, a rare inborn error of mitochondrial fatty acid oxidation. STUDY DESIGN: A questionnaire was sent to the referring physicians from 25 unselected MTP-deficient patients. RESULTS: Twenty-one patients could be included. Questionnaires about four patients were not returned. Nine (43%) patients presented with rapidly progressive clinical deterioration; six (67%) of them had hypoketotic hypoglycemia. The remaining 12 patients presented with a much more insidious disease with nonspecific chronic symptoms, including hypotonia (100%), cardiomyopathy (73%), failure to thrive, or peripheral neuropathy. Ten patients (48%) presented in the neonatal period. Mortality was high (76%), mostly attributable to cardiac involvement. Two patients who were diagnosed prenatally died despite treatment. CONCLUSION: Complete MTP deficiency often presents with nonspecific symptomatology, which makes clinical recognition difficult. Hypotonia and cardiomyopathy are common presenting features, and the differential diagnosis of an infant with these signs should include MTP deficiency. In spite of early diagnosis and treatment, only a few patients with this condition have survived.

Cardiolipin deficiency in X-linked cardioskeletal myopathy and neutropenia (Barth syndrome, MIM 302060): a study in cultured skin fibroblasts.

We determined cardiolipin concentrations in cultured skin fibroblasts of 5 patients with X-linked cardioskeletal myopathy and neutropenia (Barth syndrome, MIM 302060) and in two groups of control patients. High-performance liquid chromatography-electrospray mass spectrometry was used to quantify total cardiolipin and subclasses of cardiolipin molecular species in cultured skin fibroblasts. Total cardiolipin and cardiolipin subclasses were decreased in patients with Barth syndrome as compared with normal control patients and disease control patients. Patients with Barth syndrome have a specific decrease of various cardiolipin molecular species, foremost tetralineoyl-cardiolipin. Therefore the analysis of cardiolipin in fibroblasts offers a specific biochemical approach to detect this disorder.