Allelic Expression Imbalance Promoting a Mutant PEX6 Allele Causes Zellweger Spectrum Disorder

Zellweger spectrum disorders (ZSDs) are autosomal-recessive disorders that are caused by defects in peroxisome biogenesis due to bi-allelic mutations in any of 13 different PEX genes. Here, we identified seven unrelated individuals affected with an apparent dominant ZSD in whom a heterozygous mutant PEX6 allele (c.2578C&gt;T [p.Arg860Trp]) was overrepresented due to allelic expression imbalance (AEI). We demonstrated that AEI of PEX6 is a common phenomenon and is correlated with heterozygosity for a frequent variant in the 3' untranslated region (UTR) of the mutant allele, which disrupts the most distal of two polyadenylation sites. Asymptomatic parents, who were heterozygous for PEX c.2578C&gt;T, did not show AEI and were homozygous for the 3' UTR variant. Overexpression models confirmed that the overrepresentation of the pathogenic PEX6 c.2578T variant compared to wild-type PEX6 c.2578C results in a peroxisome biogenesis defect and thus constitutes the cause of disease in the affected individuals. AEI promoting the overrepresentation of a mutant allele might also play a role in other autosomal-recessive disorders, in which only one heterozygous pathogenic variant is identified.</p

Long-Term Cholic Acid Treatment in a Patient with Zellweger Spectrum Disorder

Zellweger spectrum disorders (ZSDs) are a subgroup of peroxisomal biogenesis disorders with a generalized defect in peroxisome function. Liver disease in ZSDs has been associated with the lack of peroxisomal β-oxidation of C27-bile acid intermediates to form primary C24-bile acids, which prevents normal physiologic feedback and leads to accumulation of hepatotoxic bile acid intermediates. Primary bile acid therapy, oral cholic acid (CA), as adjunctive treatment for ZSDs, restores physiologic feedback inhibition on bile acid synthesis and inhibits formation of hepatotoxic bile acid intermediates. Our patient is a Caucasian male diagnosed with moderately severe ZSD at age 5 months, and he received long-term CA therapy from age 16 months through 19 years old. CA treatment was well tolerated, with no reports of adverse events. His liver biopsy prior to CA therapy showed cholestasis, periportal inflammation, and bridging fibrosis. Following 5 months of CA therapy, his liver biopsy showed improvement in inflammation and no change in fibrosis. Serum liver enzymes during CA therapy improved compared to pre-therapy levels but frequently were above the upper limit of normal. At age 19 years, following several years with clinical cirrhosis with severe portal hypertension, he presented with worsening jaundice, and he was diagnosed with hepatocellular cancer (HCC). Early-onset advanced liver disease associated with ZSD and natural disease progression that is not completely suppressed with CA treatment likely caused HCC in our patient. Greater awareness is needed of the possibility of development of HCC in patients with moderately severe ZSD who survive past childhood

Clin Biochem

ObjectivesThe goal of this study was to include the quantitation of hexacosanoyl lysophosphatidylcholine, a biomarker for X-linked adrenoleukodystrophy and other peroxisomal disorders, in the routine extraction and analysis procedure used to quantitate amino acids, acylcarnitines, and succinylacetone during newborn screening. Criteria for the method included use of a single punch from a dried blood spot, one simple extraction of the punch, no high-performance liquid chromatography, and utilizing tandem mass spectrometry to quantitate the analytes.Design and methodsDried blood spot punches were extracted with a methanolic solution of stable-isotope labeled internal standards, formic acid, and hydrazine, followed by flow injection analysis\ue2\u20ac\u201celectrospray ionization\ue2\u20ac\u201ctandem mass spectrometry.ResultsQuantitation of amino acids, acylcarnitines, and hexacosanoyl lysophosphatidylcholine using this combined method was similar to results obtained using two separate methods.ConclusionsA single dried blood spot punch extracted by a rapid (45 min), simple procedure can be analyzed with high throughput (2 min per sample) to quantitate amino acids, acylcarnitines, succinylacetone, and hexacosanoyl lysophosphatidylcholine.CC999999/Intramural CDC HHS/United States2016-04-19T00:00:00Z26432925PMC483661

Genotype-phenotype correlations and disease mechanisms in PEX13-related Zellweger spectrum disorders.

BACKGROUND: Pathogenic variants in PEX-genes can affect peroxisome assembly and function and cause Zellweger spectrum disorders (ZSDs), characterized by variable phenotypes in terms of disease severity, age of onset and clinical presentations. So far, defects in at least 15 PEX-genes have been implicated in Mendelian diseases, but in some of the ultra-rare ZSD subtypes genotype-phenotype correlations and disease mechanisms remain elusive. METHODS: We report five families carrying biallelic variants in PEX13. The identified variants were initially evaluated by using a combination of computational approaches. Immunofluorescence and complementation studies on patient-derived fibroblasts were performed in two patients to investigate the cellular impact of the identified mutations. RESULTS: Three out of five families carried a recurrent p.Arg294Trp non-synonymous variant. Individuals affected with PEX13-related ZSD presented heterogeneous clinical features, including hypotonia, developmental regression, hearing/vision impairment, progressive spasticity and brain leukodystrophy. Computational predictions highlighted the involvement of the Arg294 residue in PEX13 homodimerization, and the analysis of blind docking predicted that the p.Arg294Trp variant alters the formation of dimers, impairing the stability of the PEX13/PEX14 translocation module. Studies on muscle tissues and patient-derived fibroblasts revealed biochemical alterations of mitochondrial function and identified mislocalized mitochondria and a reduced number of peroxisomes with abnormal PEX13 concentration. CONCLUSIONS: This study expands the phenotypic and mutational spectrum of PEX13-related ZSDs and also highlight a variety of disease mechanisms contributing to PEX13-related clinical phenotypes, including the emerging contribution of secondary mitochondrial dysfunction to the pathophysiology of ZSDs

PEX12 Novel Mutation: A Case Report on Iranian Girl with Childhood Onset Peroxisomal Disorder: Pseudo ALD

Objective: To report a 7 years old girl with genetic and biochemical characteristics of zellweger spectrum disorder who presented with phenotype and neuro imaging findings of adrenoleukodystrophy. Methods: Target gene sequencing was performed by using a custom designed panel for this patient with focused mutation analysis on 16 peroxisomal genes included in the panel. Sanger sequencing was used to confirm the identified mutation. Results: This patient was homozygote for a missense mutation in exon 2 of the PEX 12 gene; c.541T>G (p.Tyr181Asp) which is a conserved residue in the N-terminal region crucial for localization to peroxisomes. Her parents and healthy sister were also found to have the same heterozygote mutation. Conclusion: We suggest that PEX 12 gene mutations with a milder phenotype may be a potential candidate for posterior dominant leukodystrophy of childhood resembling X-linked ALD. This is entitled to pseudo- ALD and may be a diagnostic possibility in patients who develop ALD phenotype and neuroimaging particularly, in girls

Rare and Disabling Movement Disorders: An Indian Experience

Recent decades have seen exciting developments in the field of movement disorders. These include identification of rare clinical syndromes and use of technological advances to understand their pathogenesis. Three such disorders are discussed here. The description of the Uner Tan syndrome from Turkey and surrounding regions provoked research into the controversial field of genetically induced devolution. Such cases with few additional findings have now been described from India. Sepiapterin reductase deficiency is a rare treatable autosomal recessive form of dopa responsive dystonia. Indian literature has recently added five confirmed cases to the international database. Such cases are eminently treatable. Successful application of modern technology in understanding the pathogenesis of progressive neurodegenerative disorder has been highlighted in the section on hereditary spastic paraplegias. Hitherto undescribed subcellular organelle transport defects and their potential rectification with known drugs have been demonstrated raising hopes for their cure

Profile and outcome of children with inborn errors of metabolism in a tertiary pediatric intensive care unit in South India

Introduction: Inborn errors of metabolism (IEM) can present as acute metabolic emergencies resulting in significant morbidity or death. Good intensive care supportive management and specific metabolic crisis treatment by tertiary pediatric intensive care unit (PICU) play a crucial role in optimizing the outcomes. Objectives: We aimed to study the clinical profile and outcome of children with IEM presenting as an acute metabolic crisis in a tertiary PICU. Methods: This retrospective descriptive study was conducted in a tertiary care center in south India between June 2016 and December 2018. We included children admitted in PICU as medical emergency and diagnosed to have IEM either earlier or at the time of PICU presentation by biochemical testing (basic testing and tandem mass spectrometry [TMS], gas chromatography-mass spectrometry [GCMS] and high-performance liquid chromatography [HPLC], and/or specialized testing) and/or molecular analysis. Clinical profile, details of diagnostic workup, and outcome were collected and analyzed. Results: Out of 2815 children admitted in PICU, 15 had IEM (0.9%). Median (interquartile range) age of presentation was 15 months (10–30 months). Consanguinity was found in 80%. The most common disorder was protein metabolic disorder. Seven patients were diagnosed in the newborn period, five during evaluation for developmental delay before PICU admission, and three were newly diagnosed during PICU admission. Supportive therapy of invasive/non-invasive ventilation and peritoneal dialysis was initiated in 10 and 4, respectively. Special formula was started in nine patients. Five (33%) died in spite of intensive care management. TMS, GCMS, and HPLC yielded definitive diagnosis in 12 (80%) patients. Molecular analysis was done in 12 patients. Conclusion: The most common cause for metabolic crisis in PICU is due to protein metabolic disorder. Aggressive intensive care and IEM directed therapy can be lifesaving, but still, the mortality is high

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 with HS, and - 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 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 overlap is minimal and the diagnosis was not suggested by routine blood and skin fibroblast analyses used to detect PBDs. In conclusion, our findings define Heimler syndrome as a mild PBD, expanding the pleiotropy of mutations in PEX1 and PEX6