Dicarboxylic acylcarnitine biomarkers in peroxisome biogenesis disorders.

The peroxisome is an essential eukaryotic organelle with diverse metabolic functions. Inherited peroxisomal disorders are associated with a wide spectrum of clinical outcomes and are broadly divided into two classes, those impacting peroxisome biogenesis (PBD) and those impacting specific peroxisomal factors. Prior studies have indicated a role for acylcarnitine testing in the diagnosis of some peroxisomal diseases through the detection of long chain dicarboxylic acylcarnitine abnormalities (C16-DC and C18-DC). However, there remains limited independent corroboration of these initial findings and acylcarnitine testing for peroxisomal diseases has not been widely adopted in clinical laboratories. To explore the utility of acylcarnitine testing in the diagnosis of peroxisomal disorders we applied a LC-MS/MS acylcarnitine method to study a heterogenous clinical sample set (n = 598) that included residual plasma specimens from nineteen patients with PBD caused by PEX1 or PEX6 deficiency, ranging in severity from lethal neonatal onset to mild late onset forms. Multiple dicarboxylic acylcarnitines were significantly elevated in PBD patients including medium to long chain (C8-DC to C18-DC) species as well as previously undescribed elevations of malonylcarnitine (C3-DC) and very long chain dicarboxylic acylcarnitines (C20-DC and C22-DC). The best performing plasma acylcarnitine biomarkers, C20-DC and C22-DC, were detected at elevated levels in 100% and 68% of PBD patients but were rarely elevated in patients that did not have a PBD. We extended our analysis to residual newborn screening blood spot cards and were able to detect dicarboxylic acylcarnitine abnormalities in a newborn with a PBD caused by PEX6 deficiency. Similar to prior studies, we failed to detect substantial dicarboxylic acylcarnitine abnormalities in blood spot cards from patients with x-linked adrenoleukodystrophy (x-ald) indicating that these biomarkers may have utility in quickly narrowing the differential diagnosis in patients with a positive newborn screen for x-ald. Overall, our study identifies widespread dicarboxylic acylcarnitine abnormalities in patients with PBD and highlights key acylcarnitine biomarkers for the detection of this class of inherited metabolic disease.

Very long chain acylcarnitines and lysophosphatidylcholines in screening of peroxisomal disease in children by tandem mass spectrometry.

To investigate the value of very long chain acylcarnitine (VLCAC) and lysophosphatidylcholine (LPC) in screening of peroxisomal disease in children. Eighteen children with peroxisomal disease, including 14 cases of X-linked adrenoleukodystrophy (X-ALD group) and 4 cases of Zellweger syndrome (ZS group) diagnosed based on clinical symptoms, MRI and genetic tests were enrolled in the study; and 200 healthy children were selected as control group. Samples of dried blood spots were collected from all subjects, VLCAC and LPC in dried blood spots were extracted by solvent containing internal isotopic standards hexacosanoylcarnitine (H-C26) and C26:0 lysophosphatidylcholine (H-C26:0-LPC). The eicosanoylcarnitine (C20), docosanoylcarnitine (C22), tetracosanoylcarnitine (C24), hexacosanoylcarnitine (C26), C20:0 lysophosphatidylcholine (C20:0-LPC), C22:0 lysophosphatidylcholine (C22:0-LPC), C24:0 lysophosphatidylcholine (C24:0-LPC) and C26:0 lysophosphatidylcholine (C26:0-LPC) were detected by tandem mass spectrometry (MS/MS). The above 8 indicators and the ratios were compared among the groups using Kruskal-Wallis test and Mann-Whitney test; the contribution of each index to the disease were analyzed by partial least square method. Except C24:0-LPC/C20:0-LPC, there were significant differences in all indicators and ratios among all groups (<0.05 or <0.01). There were differences in most indicators and ratios between X-ALD group and the control group, as well as between ZS group and the control group, but there was no difference between the X-ALD group and the ZS group. PLS-DA analysis showed that the peroxisome disease group (including X-ALD group and ZS group) and the control group were able to be completely separated, and C26 had the highest variable importance for the projection (VIP) value. MS/MS detection of VLCAC and LPC can be used as a screening method for peroxisomal disease, and C26 may be a sensitive indicator for diagnosis.

Newly defined peroxisomal disease with novel ACBD5 mutation.

Peroxisomal disorders are a heterogeneous group of diseases caused by mutations in a large number of genes. One of the genetic disorders known to cause this situation is ACBD5 (Acyl-CoA binding-domain-containing-5) gene mutations that have been described in recent years. Here, we report two siblings with a novel homozygous nonsense variation (c.1297C>T, p.Arg433*) in ACBD5 (NM_145698.4) gene using Clinical Exome Sequencing (Sophia Genetics).

A Novel Mutation in PEX11ß Gene.

PEX11ß ([OMIM] 614920) mutation causes an extremely rare subgroup of peroxisomal biogenesis disorders, with only six cases reported to date. In this article, we reported a patient with episodic migraine-like attacks, delirium, mood and behavior change, polyneuropathy, and history of congenital cataract. Whole exome sequencing showed novel c.743_744delTCinsA mutation in the exon 4 of the PEX11ß gene. In contrast to previously reported patients, our case presented milder features and extended the spectrum of the clinical phenotype of this mutation. This study helps to extend the phenotype of this syndrome; besides, recognizing novel mutation variants will provide a better genotype-phenotype correlation and improve clinical clues.

Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review.

Background: D-Bifunctional protein deficiency (D-BPD) is an autosomal recessive disorder caused by peroxisomal ß-oxidation defects. According to the different activities of 2-enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase protein units, D-bifunctional protein defects can be divided into four types. The typical symptoms include hypotonia and seizures. The gene that encodes D-BP was HSD17B4, which is located in chromosome 5q23.1. Case Presentation: We report the first case of D-BPD in a Chinese patient with neonatal onset. Cosmetic malformations, severe hypotonia and seizures are prominent. The blood bile acid profile showed increased taurocholic acid, glycocholic acid, and taurochenodeoxycholic acid. Very-long-chain fatty acids (VLCFAs) revealed significant increases in hexacosanoic acid (C26:0), tetracosanoic acid/docosanoic acid (C24:0/C22:0), and hexacosanoic acid/docosanoic acid (C26:0/C22:0). Cranial MRI revealed bilateral hemispheric and callosal dysplasia, with schizencephaly in the right hemisphere. EEG showed loss of sleep-wake cycle and epileptiform discharge. Other examinations include abnormal brainstem auditory evoked potentials (BAEPs) and temporal pigmented spots on the optic disc in the right eye. After analysis by whole-exome sequencing, heterozygous c.972+1G>T in the paternal allele and c.727T>A (p.W243R) in the maternal allele were discovered. He was treated with respiratory support, formula nasogastric feeding, and antiepileptic therapy during hospitalization and died at home due to food refusal and respiratory failure at the age of 5 months. Conclusions: Whole-exome sequencing should be performed in time to confirm the diagnosis when the newborn presents hypotonia, seizures, and associated cosmetic malformations. There is still a lack of effective radical treatment. Supportive care is the main treatment, aiming at controlling symptoms of central nervous system like seizures and improving nutrition and growth. The disease has a poor outcome, and infants often die of respiratory failure within 2 years of age. In addition, heterozygous deletion variant c.972+1G>T and missense mutations c.727T>A (p.W243R) are newly discovered pathogenic variants that deserve further study.

Novel HSD17B4 Variants Cause Progressive Leukodystrophy in Childhood: Case Report and Literature Review.

D-bifunctional protein (DBP) deficiency is a peroxisomal disorder with a high degree of phenotypic heterogeneity. Some patients with DBP deficiency develop progressive leukodystrophy in childhood. We report a 6-year-old boy with moderate hearing loss who presented with developmental regression. Brain magnetic resonance imaging demonstrated progressive leukodystrophy. However, very long chain fatty acids (VLCFAs) in the plasma were at normal levels. Whole-exome sequencing revealed compound heterozygous variants in HSD17B4 (NM_000414.3:c.[350A > T];[394C > T], p.[[Asp117Val]];[[Arg132Trp]]). The c.394C > T variant has been identified in patients with DBP deficiency and is classified as likely pathogenic, while the c.350A > T variant was novel and classified as uncertain significance. Although one of the two variants was classified as uncertain significance, an accumulation of phytanic and pristanic acids was identified in the patient, confirming type III DBP deficiency. DBP deficiency should be considered as a diagnosis in children with progressive leukodystrophy and hearing loss even if VLCFAs are within normal levels.

Spastic paraplegia as the predominant phenotype in a cohort of Chinese patients with adrenoleukodystrophy.

BACKGROUND: X-linked adrenoleukodystrophy (ALD) is one of the most common peroxisomal disorders characterized by abnormal accumulation of very long-chain fatty acids (VLCFA) in plasma and tissues and caused by mutations within ABCD1. Clinically, ALD present with various phenotypes, ranging from asymptomatic type to rapidly progressive childhood cerebral form. However, no remarkable abnormality in cerebral white matter usually makes it difficult to distinguish adult ALD from hereditary spastic paraplegia (HSP). METHODS: We analyzed the features of seven Chinese ALD patients who had a primary phenotype of spastic paraplegia. Sequencing was performed in the probands and their familial members. Detailed clinical, VLCFAs test, hormone test, magnetic resonance imaging, and electromyogram are presented. RESULTS: We reported seven ALD patients from a Chinese cohort of 142 HSP patients. Genetic investigations revealed five known ABCD1 mutations (c.346G>C, c.521A>G, c.829G>T, c.1415_1416delAG, and c.1849C>T) and two novel mutations (c.454C>G, c.1452_1482del). Further auxiliary testing revealed that they had higher VLCFA and/or adrenal insufficiency. CONCLUSIONS: Our findings expand the mutation spectrum of ABCD1 and indicate that ALD represent a significant portion (4.9%, 7/142) of the spastic paraplegia entities. ALD should be considered in male patients with spastic paraplegia, even if there was no positive family history.

Chinese patients with adrenoleukodystrophy and Zellweger spectrum disorder presenting with hereditary spastic paraplegia.

INTRODUCTION: X-linked adrenoleukodystrophy (ALD) and Zellweger spectrum disorder (ZSD) are peroxisomal diseases characterized by accumulation of very long chain fatty acids (VLCFA) in plasma and tissues. Considering the wide variability of manifestation, patients of ALD and atypical ZSD are easily misdiagnosed as hereditary spastic paraplegia (HSP) on their clinical grounds. Here, we aimed to determine the frequency of peroxisome diseases and compare their phenotypic spectra with HSP. METHODS: We first applied targeted sequencing in 120 pedigrees with spastic paraplegia, and subsequently confirmed 74 HSP families. We then performed whole exome sequencing for the probands of the 46 remaining pedigrees lacking known HSP-causal genes. Detailed clinical, radiological features, and VLCFA analyses are presented. RESULTS: Seven ALD pedigrees with ABCD1 mutations and one ZSD family harboring bi-allelic mutations of PEX16 were identified. Clinically, in addition to spastic paraplegia, four ALD probands presented adrenocortical insufficiency, and the ZSD proband and her affected sister both developed thyroid problems. VLCFA analysis showed that ratios of C24/C22 and C26/C22 were specifically increased in ALD probands. Moreover, three ALD probands and the ZSD proband had abnormalities in brain or spinal imaging. CONCLUSIONS: Our study reports the first ZSD case in China that manifested spastic paraplegia, and emphasized the finding that peroxisomal diseases comprise a significant proportion (8/120) of spastic paraplegia entities. These findings extend our current understanding of the ALD and ZSD diseases.

Hematopoietic Stem Cell Transplantation in Inborn Errors of Metabolism.

Hematopoietic stem cell transplantation (HSCT) has been established as an effective therapy for selected inborn errors of metabolism. The success of HSCT in metabolic disease is best exemplified through the treatment of Hurler's syndrome, a lysosomal storage disease. Through the collaborative effort of several international centers, factors that predict successful patient and transplant outcomes have been identified. In this review, we discuss the principles that underlie the use of HSCT in metabolic diseases. We consider the clinical indications, conditioning regimens, and disease-specific follow-up for HSCT in different metabolic diseases. We highlight persisting challenges in HSCT to delay progression of certain organ systems that remain refractory to HSCT and the relatively high rates of aplastic graft failure. Finally, we evaluate the variable applicability of these principles to other inherited metabolic disorders including peroxisomal, mitochondrial, and other lysosomal storage diseases.