Measurement of very long-chain fatty acids, phytanic and pristanic acid in plasma and cultured fibroblasts by gas chromatography

Autosomal dominant Zellweger spectrum disorder caused by de novo variants in PEX14 gene

PURPOSE

Zellweger spectrum disorders (ZSDs) are known as autosomal recessive disorders caused by defective peroxisome biogenesis due to bi-allelic pathogenic variants in any of at least 13 different PEX genes. Here, we report 2 unrelated patients who present with an autosomal dominant ZSD.

METHODS

We performed biochemical and genetic studies in blood and skin fibroblasts of the patients and demonstrated the pathogenicity of the identified PEX14 variants by functional cell studies.

RESULTS

We identified 2 different single heterozygous de novo variants in the PEX14 genes of 2 patients diagnosed with ZSD. Both variants cause messenger RNA mis-splicing, leading to stable expression of similar C-terminally truncated PEX14 proteins. Functional studies indicated that the truncated PEX14 proteins lost their function in peroxisomal matrix protein import and cause increased degradation of peroxisomes, ie, pexophagy, thus exerting a dominant-negative effect on peroxisome functioning. Inhibition of pexophagy by different autophagy inhibitors or genetic knockdown of the peroxisomal autophagy receptor NBR1 resulted in restoration of peroxisomal functions in the patients' fibroblasts.

CONCLUSION

Our finding of an autosomal dominant ZSD expands the genetic repertoire of ZSDs. Our study underscores that single heterozygous variants should not be ignored as possible genetic cause of diseases with an established autosomal recessive mode of inheritance.

Differential roles for ACBD4 and ACBD5 in peroxisome-ER interactions and lipid metabolism

Peroxisomes and the endoplasmic reticulum (ER) are intimately linked subcellular organelles, physically connected at membrane contact sites. While collaborating in lipid metabolism, for example, of very long-chain fatty acids (VLCFAs) and plasmalogens, the ER also plays a role in peroxisome biogenesis. Recent work identified tethering complexes on the ER and peroxisome membranes that connect the organelles. These include membrane contacts formed via interactions between the ER protein VAPB (vesicle-associated membrane protein-associated protein B) and the peroxisomal proteins ACBD4 and ACBD5 (acyl-coenzyme A-binding domain protein). Loss of ACBD5 has been shown to cause a significant reduction in peroxisome-ER contacts and accumulation of VLCFAs. However, the role of ACBD4 and the relative contribution these two proteins make to contact site formation and recruitment of VLCFAs to peroxisomes remain unclear. Here, we address these questions using a combination of molecular cell biology, biochemical, and lipidomics analyses following loss of ACBD4 or ACBD5 in HEK293 cells. We show that the tethering function of ACBD5 is not absolutely required for efficient peroxisomal β-oxidation of VLCFAs. We demonstrate that loss of ACBD4 does not reduce peroxisome-ER connections or result in the accumulation of VLCFAs. Instead, the loss of ACBD4 resulted in an increase in the rate of β-oxidation of VLCFAs. Finally, we observe an interaction between ACBD5 and ACBD4, independent of VAPB binding. Overall, our findings suggest that ACBD5 may act as a primary tether and VLCFA recruitment factor, whereas ACBD4 may have regulatory functions in peroxisomal lipid metabolism at the peroxisome-ER interface.

Biochemical Studies in Fibroblasts to Interpret Variants of Unknown Significance in the ABCD1 Gene

Due to newborn screening for X-linked adrenoleukodystrophy (ALD), and the use of exome sequencing in clinical practice, the detection of variants of unknown significance (VUS) in the ABCD1 gene is increasing. In these cases, functional tests in fibroblasts may help to classify a variant as (likely) benign or pathogenic. We sought to establish reference ranges for these tests in ALD patients and control subjects with the aim of helping to determine the pathogenicity of VUS in ABCD1. Fibroblasts from 36 male patients with confirmed ALD, 26 healthy control subjects and 17 individuals without a family history of ALD, all with an uncertain clinical diagnosis and a VUS identified in ABCD1, were included. We performed a combination of tests: (i) a test for very-long-chain fatty acids (VLCFA) levels, (ii) a D₃-C22:0 loading test to study the VLCFA metabolism and (iii) immunoblotting for ALD protein. All ALD patient fibroblasts had elevated VLCFA levels and a reduced peroxisomal ß-oxidation capacity (as measured by the D₃-C16:0/D₃-C22:0 ratio in the D₃-C22:0 loading test) compared to the control subjects. Of the VUS cases, the VLCFA metabolism was not significantly impaired (most test results were within the reference range) in 6/17, the VLCFA metabolism was significantly impaired (most test results were within/near the ALD range) in 9/17 and a definite conclusion could not be drawn in 2/17 of the cases. Biochemical studies in fibroblasts provided clearly defined reference and disease ranges for the VLCFA metabolism. In 15/17 (88%) VUS we were able to classify the variant as being likely benign or pathogenic. This is of great clinical importance as new variants will be detected.

Mitochondrial fission factor (MFF) is a critical regulator of peroxisome maturation

Peroxisomes are highly dynamic subcellular compartments with important functions in lipid and ROS metabolism. Impaired peroxisomal function can lead to severe metabolic disorders with developmental defects and neurological abnormalities. Recently, a new group of disorders has been identified, characterised by defects in the membrane dynamics and division of peroxisomes rather than by loss of metabolic functions. However, the contribution of impaired peroxisome plasticity to the pathophysiology of those disorders is not well understood. Mitochondrial fission factor (MFF) is a key component of both the peroxisomal and mitochondrial division machinery. Patients with MFF deficiency present with developmental and neurological abnormalities. Peroxisomes (and mitochondria) in patient fibroblasts are highly elongated as a result of impaired organelle division. The majority of studies into MFF-deficiency have focused on mitochondrial dysfunction, but the contribution of peroxisomal alterations to the pathophysiology is largely unknown. Here, we show that MFF deficiency does not cause alterations to overall peroxisomal biochemical function. However, loss of MFF results in reduced import-competency of the peroxisomal compartment and leads to the accumulation of pre-peroxisomal membrane structures. We show that peroxisomes in MFF-deficient cells display alterations in peroxisomal redox state and intra-peroxisomal pH. Removal of elongated peroxisomes through induction of autophagic processes is not impaired. A mathematical model describing key processes involved in peroxisome dynamics sheds further light into the physical processes disturbed in MFF-deficient cells. The consequences of our findings for the pathophysiology of MFF-deficiency and related disorders with impaired peroxisome plasticity are discussed.

•

Peroxisomes are highly elongated in cells from patients lacking fission factor MFF.

•

Peroxisomal proteins are not uniformly distributed in highly elongated peroxisomes.

•

Peroxisomal metabolism is unaltered in MFF-deficient patients.

•

Peroxisomal elongations are stabilised through interaction with microtubules.

•

Highly elongated peroxisomes are not spared from degradation.

Selective receptor-mediated impairment of growth factor activity in neonatal- and X-linked adrenoleukodystrophy patients

Background Neonatal adrenoleukodystrophy (n-ALD) and X-linked ALD (X-ALD) patients present with demyelination, poor growth and progressive mental retardation. Growth factors are known to play a vital role in the development of children. Objective To examine the mitogenic activity of various growth factors in skin fibroblasts from n-ALD and X-ALD patients. Methods Skin fibroblast cultures from n-ALD and X-ALD patients, and controls were treated with 50 ng/mL of platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF) or insulin-like growth factor-1 (IGF-1) to examine DNA synthesis by 5-bromo-2'-deoxyuridine (BrdU) incorporation. Expression of receptors for PDGF, bFGF and IGF-1 was measured by western blotting. Serum levels of IGF-1 were assayed by enzyme-linked immunosorbent assay (ELISA). Results Fibroblasts from n-ALD and X-ALD patients had significantly (p < 0.01) less BrdU incorporation in response to fetal bovine serum (FBS). The mitogenic effect of PDGF, bFGF and IGF-1 was significantly lower in n-ALD as compared to control and X-ALD cells. X-ALD cells showed significant impairment in IGF-1-induced DNA synthesis. Expression of the FGF receptor (FGF-R) was significantly reduced in n-ALD cells. PDGF receptor remained unaffected, and IGF-1 receptor (IGF-1R) expression and serum IGF-1 levels were significantly (p < 0.01) reduced in n-ALD and X-ALD patients as compared to controls. Conclusions Growth factor activity differs in n-ALD and X-ALD patients, with marked impairment of IGF-1 function through receptor down-regulation.

Case report of dysregulation of primary bile acid synthesis in a family with X-linked adrenoleukodystrophy

RATIONALE

X-linked adrenoleukodystrophy (X-ALD) is a rare disorder caused by mutations in the ABCD1 gene, coding for peroxisomal membrane transporter adrenoleukodystrophy (ALD) protein. The disease is characterized by accumulation of very long chain fatty acids (VLCFAs) in tissues. Adult adrenomyeloneuropathy (AMN) and the cerebral inflammatory form of ALD are the main phenotypes presenting various symptoms.

PATIENT CONCERNS

We report a case of 37-year-old patient with diagnosis of X-ALD, confirmed based on elevated VLCFA concentrations and genetic testing of ABCD1 gene. The complete clinical picture in the patient indicates AMN phenotype with cerebral involvement.

DIAGNOSES

The reduced synthesis of unconjugated cholic and chenodeoxycholic acids, and the reduction to 28% to 29% of peroxisomal beta-oxidation of behenic acid and normal peroxisomal metabolism of pristanic and palmitic acid were observed in the X-ALD patient. Sanger sequencing of major genes involved in primary bile acid (BA) synthesis failed to identify pathogenic mutations of the investigated set of genes.

INTERVENTIONS

Plasma concentrations of BAs, VLCFAs, and beta-oxidation of C22:0, C16:0, and pristanic acid were studied in primary skin fibroblasts of the patient. In addition, we performed sequencing of the ABCD1, ABCD3, CYP7A1, CYP7B1, CYP27A1, HSD3B7, AKR1D1, and SLC27A5 genes in the X-ALD family.

OUTCOMES

In the Polish family affected with AMN a dysregulation of the primary BA synthesis pathway was found.

LESSONS

We have demonstrated the coincidence of the adult form of X-ALD with abnormalities in BA synthesis. We suggest that decreased synthesis of BAs may be an additional dysfunction as a consequence of the ABCD1 c.659T>C, p.(Leu220Pro) mutation and may be further evidence that disturbed cholesterol metabolism is important in the pathology of ALD.

Biochemical and clinical profiles of 52 Tunisian patients affected by Zellweger syndrome

BACKGROUND

Zellweger syndrome (ZS) is a peroxisome biogenesis disorder attributed to a mutation of the PEX genes family. The incidence of this disease in Africa and the Arab world remains unknown. This contribution is aimed at describing the clinical phenotype and biochemical features in Tunisian patients with ZS in order to improve the detection and management of this severe disorder.

METHODS

A total of 52 patients diagnosed with ZS and 60 age- and sex-matched healthy controls were included in this study. Patients were recruited during the past 21 years, and the diagnosis of ZS was based on clinical and biochemical characteristics. Plasma very long chain fatty acids (VLCFA) were analyzed using capillary gas chromatography. The estimated incidence of ZS was calculated using the Hardy-Weinberg formula.

RESULTS

The estimated incidence of ZS is 1/15,898 in Tunisia. Age at diagnosis varied between 3 days and 18 months. Severe neurological syndrome, polymalformative features, and hepatodigestive signs were observed in 100%, 67.9%, and 32% of patients, respectively. Values for plasma C26:0 and C26:0/C22:0 and C24:0/C22:0 ratios were noticeably higher in ZS patients than in controls. Distributions of values were completely different for C26:0 (0.10-0.37 vs. 0.001-0.009), C26:0/C22:0 ratio (0.11-1.29 vs. 0.003-0.090), and C24:0/C22:0 ratio (1.03-3.18 vs. 0.4-0.90) in ZS patients versus controls, respectively.

CONCLUSIONS

This study highlights the high incidence of ZS in Tunisia and the possibility of simple and reliable biochemical diagnosis, thus permitting early genetic counseling for families at risk.

ACBD5 deficiency causes a defect in peroxisomal very long-chain fatty acid metabolism

BACKGROUND

Acyl-CoA binding domain containing protein 5 (ACBD5) is a peroxisomal membrane protein with a cytosolic acyl-CoA binding domain. Because of its acyl-CoA binding domain, ACBD5 has been assumed to function as an intracellular carrier of acyl-CoA esters. In addition, a role for ACBD5 in pexophagy has been suggested. However, the precise role of ACBD5 in peroxisomal metabolism and/or functioning has not yet been established. Previously, a genetic ACBD5 deficiency was identified in three siblings with retinal dystrophy and white matter disease. We identified a pathogenic mutation in ACBD5 in another patient and studied the consequences of the ACBD5 defect in patient material and in ACBD5-deficient HeLa cells to uncover this role.

METHODS

We studied a girl who presented with progressive leukodystrophy, syndromic cleft palate, ataxia and retinal dystrophy. We performed biochemical, cell biological and molecular studies in patient material and in ACBD5-deficient HeLa cells generated by CRISPR-Cas9 genome editing.

RESULTS

We identified a homozygous deleterious indel mutation in ACBD5, leading to complete loss of ACBD5 protein in the patient. Our studies showed that ACBD5 deficiency leads to accumulation of very long-chain fatty acids (VLCFAs) due to impaired peroxisomal β-oxidation. No effect on pexophagy was found.

CONCLUSIONS

Our investigations strongly suggest that ACBD5 plays an important role in sequestering C26-CoA in the cytosol and thereby facilitates transport into the peroxisome and subsequent β-oxidation. Accordingly, ACBD5 deficiency is a novel single peroxisomal enzyme deficiency caused by impaired VLCFA metabolism, leading to retinal dystrophy and white matter disease.

The important role of biochemical and functional studies in the diagnostics of peroxisomal disorders

Peroxisomes are dynamic organelles that play an essential role in a variety of metabolic pathways. Peroxisomal dysfunction can lead to various biochemical abnormalities and result in abnormal metabolite levels, such as increased very long-chain fatty acid or reduced plasmalogen levels. The metabolite abnormalities in peroxisomal disorders are used in the diagnostics of these disorders. In this paper we discuss in detail the different diagnostic tests available for peroxisomal disorders and focus specifically on the important role of biochemical and functional studies in cultured skin fibroblasts in reaching the right diagnosis. Several examples are shown to underline the power of such studies.

Zellweger spectrum disorders: clinical manifestations in patients surviving into adulthood

INTRODUCTION

We describe the natural history of patients with a Zellweger spectrum disorder (ZSD) surviving into adulthood.

METHODS

Retrospective cohort study in patients with a genetically confirmed ZSD.

RESULTS

All patients (n = 19; aged 16-35 years) had a follow-up period of 1-24.4 years (mean 16 years). Seven patients had a progressive disease course, while 12 remained clinically stable during follow-up. Disease progression usually manifests in adolescence as a gait disorder, caused by central and/or peripheral nervous system involvement. Nine were capable of living a partly independent life with supported employment. Systematic MRI review revealed T2 hyperintense white matter abnormalities in the hilus of the dentate nucleus and/or peridentate region in nine out of 16 patients. Biochemical analyses in blood showed abnormal peroxisomal biomarkers in all patients in infancy and childhood, whereas in adolescence/adulthood we observed normalization of some metabolites.

CONCLUSIONS

The patients described here represent a distinct subgroup within the ZSDs who survive into adulthood. Most remain stable over many years. Disease progression may occur and is mainly due to cerebral and cerebellar white matter abnormalities, and peripheral neuropathy.

Heimler Syndrome Is Caused by Hypomorphic Mutations in the Peroxisome-Biogenesis Genes PEX1 and PEX6

Heimler syndrome (HS) is a rare recessive disorder characterized by sensorineural hearing loss (SNHL), amelogenesis imperfecta, nail abnormalities, and occasional or late-onset retinal pigmentation. We ascertained eight families affected by HS and, by using a whole-exome sequencing approach, identified biallelic mutations in PEX1 or PEX6 in six of them. Loss-of-function mutations in both genes are known causes of a spectrum of autosomal-recessive peroxisome-biogenesis disorders (PBDs), including Zellweger syndrome. PBDs are characterized by leukodystrophy, hypotonia, SNHL, retinopathy, and skeletal, craniofacial, and liver abnormalities. We demonstrate that each HS-affected family has at least one hypomorphic allele that results in extremely mild peroxisomal dysfunction. Although individuals with HS share some subtle clinical features found in PBDs, the diagnosis was not suggested by routine blood and skin fibroblast analyses used to detect PBDs. In conclusion, our findings define HS as a mild PBD, expanding the pleiotropy of mutations in PEX1 and PEX6.

Infantile Refsum Disease: Influence of Dietary Treatment on Plasma Phytanic Acid Levels

Infantile Refsum disease (IRD) is one of the less severe of Zellweger spectrum disorders (ZSDs), a group of peroxisomal biogenesis disorders resulting from a generalized peroxisomal function impairment. Increased plasma levels of very long chain fatty acids (VLCFA) and phytanic acid are biomarkers used in IRD diagnosis. Furthermore, an increased plasma level of phytanic acid is known to be associated with neurologic damage. Treatment of IRD is symptomatic and multidisciplinary.The authors report a 3-year-old child, born from consanguineous parents, who presented with developmental delay, retinitis pigmentosa, sensorineural deafness and craniofacial dysmorphisms. While the relative level of plasma C26:0 was slightly increased, other VLCFA were normal. Thus, a detailed characterization of the phenotype was essential to point to a ZSD. Repeatedly increased levels of plasma VLCFA, along with phytanic acid and pristanic acid, deficient dihydroxyacetone phosphate acyltransferase activity in fibroblasts and identification of the homozygous pathogenic mutation c.2528G>A (p.Gly843Asp) in the PEX1 gene, confirmed this diagnosis. Nutritional advice and follow-up was proposed aiming phytanic acid dietary intake reduction. During dietary treatment, plasma levels of phytanic acid decreased to normal, and the patient's development evaluation showed slow progressive acquisition of new competences.This case report highlights the relevance of considering a ZSD in any child with developmental delay who manifests hearing and visual impairment and of performing a systematic biochemical investigation, when plasma VLCFA are mildly increased. During dietary intervention, a biochemical improvement was observed, and the long-term clinical effect of this approach needs to be evaluated.

The neurology of rhizomelic chondrodysplasia punctata

Background

To describe the neurologic profiles of Rhizomelic chondrodysplasia punctata (RCDP); a peroxisomal disorder clinically characterized by skeletal abnormalities, congenital cataracts, severe growth and developmental impairments and immobility of joints. Defective plasmalogen biosynthesis is the main biochemical feature.

Methods

Observational study including review of clinical and biochemical abnormalities, genotype, presence of seizures and neurophysiological studies of a cohort of 16 patients with RCDP.

Results

Patients with the severe phenotype nearly failed to achieve any motor or cognitive skills, whereas patients with the milder phenotype had profound intellectual disability but were able to walk and had verbal communication skills. Eighty-eight percent of patients developed epileptic seizures. The age of onset paralleled the severity of the clinical and biochemical phenotype. Myoclonic jerks, followed by atypical absences were most frequently observed. All patients with clinical seizures had interictal encephalographic evidence of epilepsy. Visual evoked (VEP) and brain auditory potential (BAEP) studies showed initial normal latency times in 93% of patients. Deterioration of VEP occurred in a minority in both the severe and the milder phenotype. BAEP and somatosensory evoked potentials (SSEP) were more likely to become abnormal in the severe phenotype. Plasmalogens were deficient in all patients. In the milder phenotype levels of plasmalogens were significantly higher in erythrocytes than in the severe phenotype. Phytanic acid levels ranged from normal to severely increased, but had no relation with the neurological phenotype.

Conclusion

Neurodevelopmental deficits and age-related occurrence of seizures are characteristic of RCDP and are related to the rest-activity in plasmalogen biosynthesis. Evoked potential studies are more likely to become abnormal in the severe phenotype, but are of no predictive value in single cases of RCDP.

Statistical methodological issues in handling of fatty acid data: percentage or concentration, imputation and indices

Basic aspects in the handling of fatty acid-data have remained largely underexposed. Of these, we aimed to address three statistical methodological issues, by quantitatively exemplifying their imminent confounding impact on analytical outcomes: (1) presenting results as relative percentages or absolute concentrations, (2) handling of missing/non-detectable values, and (3) using structural indices for data-reduction. Therefore, we reanalyzed an example dataset containing erythrocyte fatty acid-concentrations of 137 recurrently depressed patients and 73 controls. First, correlations between data presented as percentages and concentrations varied for different fatty acids, depending on their correlation with the total fatty acid-concentration. Second, multiple imputation of non-detects resulted in differences in significance compared to zero-substitution or omission of non-detects. Third, patients’ chain length-, unsaturation-, and peroxidation-indices were significantly lower compared to controls, which corresponded with patterns interpreted from individual fatty acid tests. In conclusion, results from our example dataset show that statistical methodological choices can have a significant influence on outcomes of fatty acid analysis, which emphasizes the relevance of: (1) hypothesis-based fatty acid-presentation (percentages or concentrations), (2) multiple imputation, preventing bias introduced by non-detects; and (3) the possibility of using (structural) indices, to delineate fatty acid-patterns thereby preventing multiple testing.

Lymphoblastoid cell lines for diagnosis of peroxisome biogenesis disorders

Peroxisome biogenesis disorders (PBDs) are a group of autosomal-recessive developmental and progressive metabolic diseases leading to the Zellweger spectrum (ZS) phenotype in most instances. Diagnosis of clinically suspected cases can be difficult because of extensive genetic heterogeneity and large spectrum of disease severity. Furthermore, a second group of peroxisomal diseases caused by deficiencies of single peroxisomal enzymes can show an indistinguishable clinical phenotype. The diagnosis of these peroxisomal disorders relies on the clinical presentation, the biochemical parameters in plasma and erythrocyte membranes, and genetic testing as the final step. Analysis of patients' cells is frequently required during the diagnostic process, e.g., for complementation analysis to identify the affected gene before sequencing. In the cases with unclear clinical or biochemical presentation, patients' cells are analyzed to prove PBD or to demonstrate biochemical abnormalities that might be elusive in plasma. Cell lines from skin fibroblast that are usually generated for diagnostic workup are not available in all instances, mainly because the required skin biopsy is invasive and sometimes denied by parents. An alternative cellular system has not been analyzed sufficiently. In this study, we evaluated the alternative use of lymphoblastoid cell lines (LCLs), derived from a peripheral blood sample, in the diagnostic process for PBD. LCLs were suitable for immunofluorescence visualization of peroxisomal enzymes, complementation analysis, and the biochemical analysis to differentiate between control and PBD LCL. LCLs are therefore an easily obtainable alternative cellular system for a detailed PBD diagnostic workup with a reliability of diagnostic results equal to those of skin fibroblasts.

A mutation in PEX19 causes a severe clinical phenotype in a patient with peroxisomal biogenesis disorder

Peroxisomal biogenesis disorders (PBD) are groups of inherited neurometabolic disorders caused by defects in PEX genes. We report on a female infant, born to a consanguineous parents (first degree cousins), who presented with inactivity, poor sucking, and hypotonia early in the neonatal period. She had subtle dysmorphic features. Liver function tests were impaired with raised liver enzymes, conjugated and unconjugated hyperbilirubinemia. CT of the brain showed diffuse bilateral changes. She developed seizures with an abnormal EEG. Plasma very long chain fatty acid analysis showed high C26:0 levels and increasedC26:0/C22:0 and C24:0/C22:0 ratios, which is consistent with a PBD. Studies in fibroblasts including plasmalogen biosynthesis, peroxisomal fatty acid alfa and beta oxidation confirmed the diagnosis of PBD. Immunofluoresence microscopy revealed the absence of peroxisomes in fibroblasts. The patient was assigned to the PEX19 complementation group. Subsequent mutation analysis of the PEX19 gene revealed homozygosity for a c.320delA frameshift mutation. The patient had a stormy course with multiple admissions to the pediatric intensive care unit with pneumonia, liver impairment, sepsis, and epilepsy. At 1 year of age she developed metabolic acidosis with normal anion gap, proteinuria, aminoaciduria, and glucosuria consistent with a renal tubular defect. Abdominal ultrasound showed multiple gallstones. Other causes of gallstones like haemoglobinopathy were excluded. So far, only two siblings had been reported with mutations in the PEX19 gene. Our patient showed a previously unrecognized association of gallstones and a renal tubular defect with a PBD.

Rhizomelic chrondrodysplasia punctata type 2 resulting from paternal isodisomy of chromosome 1

Rhizomelic chondrodysplasia punctata (RCDP) is an autosomal-recessive disorder resulting from mutations in one of three peroxisomal genes essential for ether lipid biosynthesis, PEX7 (RCDP1), GNPAT (RCDP2), and AGPS (RCDP3). Affected patients have characteristic features including shortening of the proximal long bones, epiphyseal stippling, bilateral cataracts, growth and developmental delays. Whereas the majority of patients have RCDP type 1, around 5% have RCDP type 2 or 3. We identified a patient with RCDP type 2 and an apparent homozygous deletion, c.1428delC, after full sequencing of his GNPAT genes. The father was heterozygous for this mutation, while sequencing of the maternal GNPAT genes revealed only wild-type sequence. Southern analyses performed on parental gDNA did not show evidence of a maternal gene deletion. Amplification and fragment analysis of dinucleotide repeat markers spanning chromosome 1 in the patient and both parents revealed paternal uniparental inheritance. We discuss the potential mechanisms causing uniparental disomy (UPD) in this patient and review the literature on chromosome 1 UPD. The absence of non-RCDP clinical features in this patient was consistent with previous literature supporting the absence of imprinted genes on chromosome 1. This first description of RCDP caused by UPD dramatically changes the parental recurrence risk, highlighting the value of obtaining parental genotypes when the proband has a putative homozygous mutation by sequence analysis.

Plasma and erythrocyte fatty acid patterns in patients with recurrent depression: a matched case-control study

Background

The polyunsaturated fatty acid (PUFA) composition of (nerve) cell membranes may be involved in the pathophysiology of depression. Studies so far, focussed mainly on omega-3 and omega-6 PUFAs. In the present study, saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and PUFAs of the omega-3, -6 and -9 series in plasma and erythrocytes of patients with recurrent major depressive disorder (MDD-R) were compared with controls.

Methodology and Principal Findings

We carried out a case-control study. The sample consisted of 137 patients with MDD-R and 65 matched non-depressed controls. In plasma and erythrocytes of patients with MDD-R the concentrations of most of the SFAs and MUFAs, and additionally erythrocyte PUFAs, all with a chain length >20 carbon (C) atoms, were significantly lower than in the controls. In contrast, the concentrations of most of the shorter chain members (≤18C) of the SFAs and MUFAs were significantly higher in the patients. Estimated activities of several elongases in plasma of patients were significantly altered, whereas delta-9 desaturase activity for C14∶0 and C18∶0 was significantly higher.

Conclusions/Significance

The fatty acid status of patients with MDD-R not only differs with regard to omega-3 and omega-6 PUFAs, but also concerns other fatty acids. These alterations may be due to: differences in diet, changes in synthesizing enzyme activities, higher levels of chronic (oxidative) stress but may also result from adaptive strategies by providing protection against enhanced oxidative stress and production of free radicals.

A Pex7 hypomorphic mouse model for plasmalogen deficiency affecting the lens and skeleton

Rhizomelic chondrodysplasia punctata type 1 is a peroxisome biogenesis disorder with the clinical features of rhizomelia, abnormal epiphyseal calcifications, congenital cataracts, and profound growth and developmental delays. It is a rare autosomal recessive disorder, caused by defects in the peroxisome receptor, PEX7. The pathology results from a deficiency of plasmalogens, a critical class of ether phospholipids whose functions are largely unknown. To study plasmalogens in an animal model, avoid early mortality and facilitate therapeutic investigations in this disease, we engineered a hypomorphic mouse model in which Pex7 transcript levels are reduced to less than 5% of wild type. These mice are born in expected ratios, are fertile and have a normal life span. However, they are petite and develop early cataracts. Further investigations showed delayed endochondral ossification and abnormalities in lens fibers. The biochemical features of reduced Pex7 function were reproduced in this model, including tissue plasmalogen deficiency, phytanic acid accumulation, reduced import of Pex7 ligands and consequent defects in plasmalogen biosynthesis and phytanic acid oxidation. Dietary supplementation with batyl alcohol, a plasmalogen precursor, recovered ether phospholipids in blood, but did not alter the clinical phenotype. The relatively mild phenotype of these mice mimics patients with milder PEX7 defects, and highlights the skeleton and lens as sensitive markers of plasmalogen deficiency. The role of plasmalogens in the normal function of these tissues at various ages can now be studied and additional therapeutic interventions tested in this model.

Ataxia with loss of Purkinje cells in a mouse model for Refsum disease

Refsum disease is caused by a deficiency of phytanoyl-CoA hydroxylase (PHYH), the first enzyme of the peroxisomal alpha-oxidation system, resulting in the accumulation of the branched-chain fatty acid phytanic acid. The main clinical symptoms are polyneuropathy, cerebellar ataxia, and retinitis pigmentosa. To study the pathogenesis of Refsum disease, we generated and characterized a Phyh knockout mouse. We studied the pathological effects of phytanic acid accumulation in Phyh(-/-) mice fed a diet supplemented with phytol, the precursor of phytanic acid. Phytanic acid accumulation caused a reduction in body weight, hepatic steatosis, and testicular atrophy with loss of spermatogonia. Phenotype assessment using the SHIRPA protocol and subsequent automated gait analysis using the CatWalk system revealed unsteady gait with strongly reduced paw print area for both fore- and hindpaws and reduced base of support for the hindpaws. Histochemical analyses in the CNS showed astrocytosis and up-regulation of calcium-binding proteins. In addition, a loss of Purkinje cells in the cerebellum was observed. No demyelination was present in the CNS. Motor nerve conduction velocity measurements revealed a peripheral neuropathy. Our results show that, in the mouse, high phytanic acid levels cause a peripheral neuropathy and ataxia with loss of Purkinje cells. These findings provide important insights in the pathophysiology of Refsum disease.

Clinical and biochemical spectrum of D-bifunctional protein deficiency

OBJECTIVE

D-bifunctional protein deficiency is an autosomal recessive inborn error of peroxisomal fatty acid oxidation. Although case reports and small series of patients have been published, these do not give a complete and balanced picture of the clinical and biochemical spectrum associated with this disorder.

METHODS

To improve early recognition, diagnosis, prognosis, and management of this disorder and to provide markers for life expectancy, we performed extensive biochemical studies in a large cohort of D-bifunctional protein-deficient patients and sent out questionnaires about clinical signs and symptoms to the responsible physicians.

RESULTS

Virtually all children presented with neonatal hypotonia and seizures and died within the first 2 years of life without achieving any developmental milestones. However, within our cohort, 12 patients survived beyond the age of 2 years, and detailed information on 5 patients with prolonged survival (> or =7.5 years) is provided.

INTERPRETATION

Biochemical analyses showed that there is a clear correlation between several biochemical parameters and survival of the patient, with C26:0 beta-oxidation activity in cultured skin fibroblasts being the best predictive marker for life expectancy. Remarkably, three patients were identified without biochemical abnormalities in plasma, stressing that D-bifunctional protein deficiency cannot be excluded when all peroxisomal parameters in plasma are normal.

Rotenone-like action of the branched-chain phytanic acid induces oxidative stress in mitochondria

Phytanic acid (Phyt) increase is associated with the hereditary neurodegenerative Refsum disease. To elucidate the still unclear toxicity of Phyt, mitochondria from brain and heart of adult rats were exposed to free Phyt. Phyt at low micromolar concentrations (maximally: 100 nmol/mg of protein) enhances superoxide (O(2)(.))(2) generation. Phyt induces O(2)(.) in state 3 (phosphorylating), as well as in state 4 (resting). Phyt stimulates O(2)(.) generation when the respiratory chain is fed with electrons derived from oxidation of glutamate/malate, pyruvate/malate, or succinate in the presence of rotenone. With succinate alone, Phyt suppresses O(2)(.) generation caused by reverse electron transport from succinate to complex I. The enhanced O(2)(.) generation by Phyt in state 4 is in contrast to the mild uncoupling concept. In this concept uncoupling by nonesterified fatty acids should abolish O(2)(.) generation. Stimulation of O(2)(.) generation by Phyt is paralleled by inhibition of the electron transport within the respiratory chain or electron leakage from the respiratory chain. The interference of Phyt with the electron transport was demonstrated by inhibition of state 3- and p-trifluoromethoxyphenylhydrazone (FCCP)-dependent respiration, inactivation of the NADH-ubiquinone oxidoreductase complex in permeabilized mitochondria, decrease in reduction of the synthetic electron acceptor 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide in state 4, and increase of the mitochondrial NAD(P)H level in FCCP-uncoupled mitochondria. Thus, we suggest that complex I is the main site of Phyt-stimulated O(2)(.) generation. Furthermore, inactivation of aconitase and oxidation of the mitochondrial glutathione pool show that enhanced O(2)(.) generation with chronic exposure to Phyt causes oxidative damage.

Effect of dehydroepiandrosterone supplementation on fatty acid and hormone levels in patients with X-linked adrenoleucodystrophy

OBJECTIVE

In X-linked adrenoleucodystrophy (X-ALD) the peroxisomal beta-oxidation of saturated very long-chain fatty acids (VLCFAs; carbon length > 22 atoms) is impaired. These fatty acids accumulate in blood and tissues, in particular in the nervous system, adrenal cortex and testis. Most patients have a primary adrenocortical insufficiency with low levels of cortisol and dehydroepiandrosterone (DHEA) and its sulphate ester (DHEA-S), collectively called DHEA(S). Surprisingly, very low plasma levels of DHEA(S) may be found when plasma cortisol and ACTH levels are normal. In animal studies DHEA administration had a peroxisome proliferating effect and induced the expression of peroxisomal enzymes involved in the beta-oxidation of fatty acids.

PATIENTS AND DESIGN

To study the effect of DHEA on fatty acids in X-ALD patients, we conducted a randomized double-blind study in which 14 men (age range 21-63 years) and one boy (12 years) received 50 mg of DHEA or placebo for 3 months, followed by a 1-month wash-out period, then 3 months of placebo or vice versa.

RESULTS

A significant rise was seen in the plasma levels of DHEA-S, Delta4-androstenedione and IGF-I. The elevated saturated VLCFAs in plasma and erythrocytes did not change. However, in erythrocytes significant decreases were found in the total amount of fatty acids, in C16:0, C18:0 and in C20:4omega-6, C22:5omega-6, C18:1omega-9, C20:1omega-9 and C20:3omega-9. In plasma, decreases were found for C18:1omega-9 and increases for C20:1omega-9.

CONCLUSIONS

Dehydroepiandrosterone supplementation for 3 months did not lower the elevated plasma levels of saturated very long-chain fatty acids in patients with X-linked adrenoleucodystrophy. Instead, a decrease in saturated and mono- and polyunsaturated fatty acids in erythrocytes and plasma was found. An increase of C20:1omega-9 was found in plasma only.

Mutation analysis of PEX7 in 60 probands with rhizomelic chondrodysplasia punctata and functional correlations of genotype with phenotype

PEX7 encodes the cytosolic receptor for the set of peroxisomal matrix enzymes targeted to the organelle by the peroxisome targeting signal 2 (PTS2). Mutations in PEX7 cause rhizomelic chondrodysplasia punctata (RCDP), a distinct peroxisome biogenesis disorder. In previous work we described three novel PEX7 mutant alleles, including one, L292X, with a high frequency due to a founder effect. We have now extended our analysis to 60 RCDP probands and identified a total of 24 PEX7 alleles, accounting for 95% of the mutant PEX7 genes in our sample. Of these, 50% are L292X, 13% are IVS9+1G>C, and the remainder are mostly private. IVS9+1G>C occurs on at least three different haplotypes and thus appears to result from recurrent mutation. The phenotypic spectrum of RCDP is broader than commonly recognized and includes minimally affected individuals at the mild end of the spectrum. To relate PEX7 genotype and phenotype, we evaluated the consequence of the disease mutation on PEX7 RNA by Northern analysis and RT/PCR. We evaluated the function of the encoded Pex7 protein (Pex7p) by expressing selected alleles in fibroblasts from RCDP patients and assaying their ability to restore import of a PTS2 marker protein. We find that residual activity of mutant Pex7p and reduced amounts of normal Pex7p are associated with milder and variant phenotypes.

Dissection of transient oxidative stress response in Saccharomyces cerevisiae by using DNA microarrays

Yeast cells were grown in glucose-limited chemostat cultures and forced to switch to a new carbon source, the fatty acid oleate. Alterations in gene expression were monitored using DNA microarrays combined with bioinformatics tools, among which was included the recently developed algorithm REDUCE. Immediately after the switch to oleate, a transient and very specific stress response was observed, followed by the up-regulation of genes encoding peroxisomal enzymes required for fatty acid metabolism. The stress response included up-regulation of genes coding for enzymes to keep thioredoxin and glutathione reduced, as well as enzymes required for the detoxification of reactive oxygen species. Among the genes coding for various isoenzymes involved in these processes, only a specific subset was expressed. Not the general stress transcription factors Msn2 and Msn4, but rather the specific factor Yap1p seemed to be the main regulator of the stress response. We ascribe the initiation of the oxidative stress response to a combination of poor redox flux and fatty acid-induced uncoupling of the respiratory chain during the metabolic reprogramming phase.

Significantly reduced docosahexaenoic and docosapentaenoic acid concentrations in erythrocyte membranes from schizophrenic patients compared with a carefully matched control group

BACKGROUND

Fatty acid research in schizophrenia has demonstrated an altered cell membrane phospholipid metabolism. Erythrocyte membrane phospholipid composition closest reflects that of neuronal membranes.

METHODS

(Poly)(un)saturated fatty acid concentrations were measured in the erythrocyte membranes of 19, consecutively admitted, medicated young schizophrenic patients and then compared with matched control subjects. Psychiatric symptomatology was rated with the Positive and Negative Symptom Scale and Montgomery-Asberg Depression Rating Scale. Because diet, hormones, and cannabis influence fatty acid metabolism, we included these factors in our study.

RESULTS

The most distinctive findings concerned the omega-3 series: C22:5 omega-3, C22:6 omega-3 (docosahexaenoic acid), and the sum of omega-3 fatty acids were significantly decreased. Interestingly, C20:4 omega-6 (arachidonic acid) was not lowered. In the omega-9 series, higher levels of C22:1 omega-9 and lower levels its elongation product, C24:1 omega-9 (nervonic acid), were found. Interestingly, the other arm of the desaturation-elongation sequence of C18:1 omega-9, C20:3 omega-9, was lower in patients. The total omega-9 fatty acid levels were also lower in patients.

CONCLUSIONS

Significant differences in erythrocyte fatty acid composition were found. The differences were not due to diet or hormonal status and could not be explained by the medication or cannabis use. No consistent pattern emerged from the different fatty acid abnormalities and the clinical symptom scores.

Lovastatin therapy for X-linked adrenoleukodystrophy: clinical and biochemical observations on 12 patients

X-linked adrenoleukodystrophy (X-ALD) is a progressive demyelinating disorder whose neurological signs and symptoms can manifest in childhood as cerebral ALD or in adulthood in the form of a progressive myelopathy (AMN). The consistent metabolic abnormality in all forms of X-ALD is an inherited defect in the peroxisomal beta-oxidation of very long chain (VLC) fatty acids (>C(22:0)) which may in turn lead to a neuroinflammatory process associated with demyelination of the cerebral white matter. The current treatment for X-ALD with Lorenzo's oil aims to lower the excessive quantities of VLC fatty acids that accumulate in the patients' plasma and tissues, but does not directly address the inflammatory process in X-ALD. We have previously demonstrated that lovastatin and other 3-HMG-CoA reductase inhibitors are capable of normalizing VLC fatty acid levels in primary skin fibroblasts derived from X-ALD patients. Lovastatin can block the induction of inducible nitric oxide synthase and proinflammatory cytokines in astrocytes, microglia, and macrophages in vitro. In a preliminary report, we demonstrated that lovastatin therapy can normalize VLC fatty acids in the plasma of patients with X-ALD. Here we report our clinical and biochemical observations on 12 patients with X-ALD who were treated with lovastatin for up to 12 months. Our results show that the high plasma levels of hexacosanoic acid (C(26:0)) showed a decline from pretreatment values within 1 to 3 months of starting therapy with 40 mg of lovastatin per day and stabilized at various levels during a period of observation up to 12 months. The percentage decline from pretreatment values varied and did not correlate with the type of ALD gene mutation (point mutation versus gene deletion). In 6 patients, in whom red cell membrane fatty acid composition was studied, a mean correction of 50% of the excess C(26:0) was observed after 6 months of therapy suggesting sustained benefit. In a few patients who discontinued lovastatin therapy plasma C(26:0) levels reverted to pretreatment values suggesting a cause and effect relationship between these events. Two patients dropped out of the study claiming no clinical benefit, 1 was withdrawn due to adverse effects, and an adult patient with cerebral involvement died during the study. A 10-year-old boy with severe cerebral involvement showed worsening of his neurological status. All patients with AMN remained neurologically stable or showed modest subjective improvement. All patients who did not have Addison's disease at the time of enrollment maintained normal adrenal function throughout the study. The implications of our findings for developing an effective therapy for X-ALD are discussed.

Plasma very long chain fatty acids in 3,000 peroxisome disease patients and 29,000 controls

The assay of plasma very long chain fatty acids (VLCFAs), developed in our laboratory in 1981, has become the most widely used procedure for the diagnosis of X-linked adrenoleukodystrophy (X-ALD) and other peroxisomal disorders. We present here our 17 years' experience with this assay. Three VLCFA parameters, the level of hexacosanoic acid (C26:0), the ratio of C26:0 to tetracosanoic acid (C24:0), and of C26:0 to docosanoic acid (C22:0), were measured in 1,097 males (hemizygotes) with X-ALD, 1,282 women heterozygous for this disorder, including 379 obligate heterozygotes, 797 patients with other peroxisomal disorders, and 29,600 control subjects. All X-ALD hemizygotes who had not previously received Lorenzo's oil or a diet with a high erucic acid content had increased VLCFA levels, but the application of a discriminant function based on all three measurements is required to avoid the serious consequences of a false-negative result. VLCFA levels are increased at day of birth, thus providing the potential for neonatal mass screening, are identical in the childhood and adult forms, and do not change with age. Eighty-five percent of obligate heterozygotes had abnormally high VLCFA levels, but a normal result does not exclude carrier status. VLCFA levels were increased in all patients homozygous for Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum's disease, and in patients with deficiencies of peroxisomal acyl-coenzyme A oxidase, bifunctional enzyme, and 3-oxoacyl-coenzyme A thiolase. In these patients the degree of VLCFA excess correlated with clinical severity.

Lovastatin and sodium phenylacetate normalize the levels of very long chain fatty acids in skin fibroblasts of X- adrenoleukodystrophy

The present study underlines the importance of lovastatin, an inhibitor of 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase, and the sodium salt of phenylacetic acid (NaPA), an inhibitor of mevalonate pyrophosphate decarboxylase, in normalizing the pathognomonic accumulation of saturated very long chain fatty acids (VLCFA) in cultured skin fibroblasts of X-adrenoleukodystrophy (X-ALD) in which the ALD gene is either mutated or deleted. Lovastatin or NaPA alone or in combination stimulated the beta-oxidation of lignoceric acid (C24:0) and normalized the elevated levels of VLCFA in skin fibroblasts of X-ALD. Ability of lovastatin and NaPA to normalize the pathognomonic accumulation of VLCFA in skin fibroblasts of X-ALD may identify these drugs as possible therapeutics for X-ALD.

Abnormality in catalase import into peroxisomes leads to severe neurological disorder

Peroxisomal disorders are lethal inherited diseases caused by either defects in peroxisome assembly or dysfunction of single or multiple enzymatic function(s). The peroxisomal matrix proteins are targeted to peroxisomes via the interaction of peroxisomal targeting signal sequences 1 and 2 (PTS1 or PTS2) with their respective cytosolic receptors. We have studied human skin fibroblast cell lines that have multiple peroxisomal dysfunctions with normal packaging of PTS1 and PTS2 signal-containing proteins but lack catalase in peroxisomes. To understand the defect in targeting of catalase to peroxisomes and the loss of multiple enzyme activities, we transfected the mutant cells with normal catalase modified to contain either PTS1 or PTS2 signal sequence. We demonstrate the integrity of these pathways by targeting catalase into peroxisomes via PTS1 or PTS2 pathways. Furthermore, restoration of peroxisomal functions by targeting catalase-SKL protein (a catalase fused to the PTS1 sequence) to peroxisomes indicates that loss of multiple functions may be due to their inactivation by H2O2 or other oxygen species in these catalase-negative peroxisomes. In addition to enzyme activities, targeting of catalase-SKL chimera to peroxisomes also corrected the in situ levels of fatty acids and plasmalogens in these mutant cell lines. In normal fibroblasts treated with aminotriazole to inhibit catalase, we found that peroxisomal functions were inhibited to the level found in mutant cells, an observation that supports the conclusion that multiple peroxisomal enzyme defects in these patients are caused by H2O2 toxicity in catalase-negative peroxisomes. Moreover, targeting of catalase to peroxisomes via PTS1 and PTS2 pathways in these mutant cell lines suggests that there is another pathway for catalase import into peroxisomes and that an abnormality in this pathway manifests as a peroxisomal disease.