[Show abstract][Hide abstract] ABSTRACT: Mucopolysaccharidosis type IIIA (Sanfilippo A syndrome), a fatal childhood-onset neurodegenerative disease with mild facial, visceral and skeletal abnormalities, is caused by an inherited deficiency of the enzyme N-sulfoglucosamine sulfohydrolase (SGSH; sulfamidase). More than 100 mutations in the SGSH gene have been found to reduce or eliminate its enzymatic activity. However, the molecular understanding of the effect of these mutations has been confined by a lack of structural data for this enzyme. Here, the crystal structure of glycosylated SGSH is presented at 2 Å resolution. Despite the low sequence identity between this unique N-sulfatase and the group of O-sulfatases, they share a similar overall fold and active-site architecture, including a catalytic formylglycine, a divalent metal-binding site and a sulfate-binding site. However, a highly conserved lysine in O-sulfatases is replaced in SGSH by an arginine (Arg282) that is positioned to bind the N-linked sulfate substrate. The structure also provides insight into the diverse effects of pathogenic mutations on SGSH function in mucopolysaccharidosis type IIIA and convincing evidence for the molecular consequences of many missense mutations. Further, the molecular characterization of SGSH mutations will lay the groundwork for the development of structure-based drug design for this devastating neurodegenerative disorder.
[Show abstract][Hide abstract] ABSTRACT: Peroxisomes are ubiquitous and dynamic organelles that house many important pathways of cellular metabolism. In recent years it has been demonstrated that mitochondria are tightly connected with peroxisomes and are defective in several peroxisomal diseases. Indeed, these two organelles share metabolic routes as well as resident proteins and, at least in mammals, are connected via a vesicular transport pathway. However the exact extent of cross-talk between peroxisomes and mitochondria remains unclear. Here we used a combination of high throughput genetic manipulations of yeast libraries alongside high content screens to systematically unravel proteins that affect the transport of peroxisomal proteins and peroxisome biogenesis. Follow up work on the effector proteins that were identified revealed that peroxisomes are not randomly distributed in cells but are rather localized to specific mitochondrial subdomains such as mitochondria-ER junctions and sites of acetyl-CoA synthesis. Our approach highlights the intricate geography of the cell and suggests an additional layer of organization as a possible way to enable efficient metabolism. Our findings pave the way for further studying the machinery aligning mitochondria and peroxisomes, the role of the juxtaposition, as well as its regulation during various metabolic conditions. More broadly, the approaches used here can be easily applied to study any organelle of choice, facilitating the discovery of new aspects in cell biology.
[Show abstract][Hide abstract] ABSTRACT: We aimed to delineate the clinical and genetic spectrum of ATP1A3-related disorders and recognition of a potential genotype-phenotype correlation.
We identified 16 new patients with alternating hemiplegia of childhood (AHC) and 3 new patients with rapid-onset dystonia-parkinsonism (RDP) and included these as well as the clinical and molecular findings of all previously reported 164 patients with mutation-positive AHC and RDP in our analyses.
Major clinical characteristics shared in common by AHC and RDP comprise a strikingly asymmetric, predominantly dystonic movement disorder with rostrocaudal gradient of involvement and physical, emotional, or chemical stressors as triggers. The clinical courses include an early-onset polyphasic for AHC, a later-onset mono- or biphasic for RDP, as well as intermediate forms. Meta-analysis of the 8 novel and 38 published ATP1A3 mutations shows that the ones affecting transmembrane and functional domains tend to be associated with AHC as the more severe phenotype. The majority of mutations are located in exons 8, 14, 17, and 18.
AHC and RDP constitute clinical prototypes in a continuous phenotypic spectrum of ATP1A3-related disorders. Intermediate phenotypes combining criteria of both conditions are increasingly recognized. Efficient stepwise mutation analysis of the ATP1A3 gene may prioritize those exons where current state of knowledge indicates mutational clusters.
[Show abstract][Hide abstract] ABSTRACT: Pediatric multiple sclerosis (MS) clinical and incidence data have been reported for several countries but valid age dependent incidence data are not yet available. The true incidence of pediatric MS in Germany was estimated and the clinical characteristics at diagnosis according to the 2005 McDonald criteria are described.
Between 2009 and 2011 active prospective nationwide surveillance for MS in children and adolescents ≤15 years included all pediatric hospitals, MS centers and private practices specialized in MS. Data were adjusted for under-reporting by capture-recapture from an independent second source.
The estimated incidence of pediatric MS was 0.64 per 100 000 person-years with clear increase from age group ≤10 (0.09/100 000) to 2.64 per 100 000 in age group 14-15 years. All had relapsing-remitting disease with polysymptomatic onset in half of the cases. Spinal MRI with positive findings in two-thirds of patients contributed to diagnosis.
Using an active prospective surveillance system and the McDonald criteria for first MS diagnosis the age-related incidence of pediatric MS in Germany was uncovered and is more common than in previous estimates. Thorough application of McDonald criteria and inclusion of spinal MRI data allowed for early diagnosis in almost 90% of cases.
European Journal of Neurology 01/2014; · 4.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mutations in the ATP1A3 gene are associated with rapid-onset dystonia-parkinsonism (RDP) and alternating hemiplegia of childhood (AHC) as well as RDP/AHC intermediate presentations. Phenotypic diversity is being recognized. In order to identify ATP1A3-related phenotypes not meeting the classical criteria for RDP or AHC we lowered the threshold for mutation analysis in clinical presentations resembling AHC or RDP. A novel heterozygous ATP1A3 missense mutation c.2600G > A (p.Gly867Asp, G867D) was detected in a 15-year-old girl. Her clinical phenotype is partially consistent with an intermediate presentation between alternating hemiplegia of childhood and rapid-onset dystonia-parkinsonism and comprises additional yet unreported features. With onset at 4½ years of age recurrent paroxysmal flaccid hemiplegia alternating in laterality was triggered by watching television or playing computer games. Occlusion of both eyes reliably stopped the plegic attacks with the patient remaining awake. Our observation further widens the phenotypic spectrum associated with ATP1A3 mutations.
Journal of the neurological sciences 01/2014; · 2.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Multiple sclerosis (MS) onset before puberty is extremely rare and establishment of diagnosis is often difficult due to atypical presentation. The study aims to identify the typical presentation of MS in this age group.
Pediatric MS patients were identified from the database of the Center for Multiple Sclerosis in Childhood and Adolescence at the University Medical Center Göttingen, Germany. Inclusion criteria were a relapsing-remitting initial disease course and minimum disease duration of 4 years.
Forty-seven pre-pubertal (<11 years) and 41 post-pubertal (14-16 years) MS patients were compared. Before puberty an even gender ratio was found. The pre-pubertal patients were more likely to have a polysymptomatic severe first attack with motor and brainstem involvement, sphincter dysfunction, cognitive disturbances and milder residual neurological sequelae after the first episode whilst the post-pubertal patients predominantly presented with optic neuritis and sensory symptoms. The initial symptom pattern prevailed over the first 2 years of disease. Presentation of pre-pubertal boys and girls did not differ significantly.
To facilitate early diagnosis it is important to recognize that pre-pubertal MS presents with a specific pattern of symptoms that is maintained over the first two disease years.
European Journal of Neurology 12/2013; · 4.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: X-linked creatine transport (CRTR) deficiency, caused by mutations in the SLC6A8 gene, leads to intellectual disability, speech delay, epilepsy, and autistic behavior in hemizygous males. Additional diagnostic features are depleted brain creatine levels and increased creatine/creatinine ratio (cr/crn) in urine. In heterozygous females the phenotype is highly variable and diagnostic hallmarks might be inconclusive. This survey aims to explore the intrafamilial variability of clinical and brain proton Magnetic Resonance Spectroscopy (MRS) findings in males and females with CRTR deficiency. X-chromosome exome sequencing identified a novel missense mutation in the SLC6A8 gene (p.G351R) in a large family with X-linked intellectual disability. Detailed clinical investigations including neuropsychological assessment, measurement of in vivo brain creatine concentrations using quantitative MRS, and analyses of creatine metabolites in urine were performed in five clinically affected family members including three heterozygous females and one hemizygous male confirming the diagnosis of CRTR deficiency. The severe phenotype of the hemizygous male was accompanied by most distinct aberrations of brain creatine concentrations (-83% in gray and -79% in white matter of age-matched normal controls) and urinary creatine/creatinine ratio. In contrast, the heterozygous females showed varying albeit generally milder phenotypes with less severe brain creatine (-50% to -33% in gray and -45% to none in white matter) and biochemical urine abnormalities. An intrafamilial correlation between female phenotype, brain creatine depletion, and urinary creatine abnormalities was observed. The combination of powerful new technologies like exome-next-generation sequencing with thorough systematic evaluation of patients will further expand the clinical spectrum of neurometabolic diseases.
[Show abstract][Hide abstract] ABSTRACT: Fragile X syndrome is caused by the loss of FMRP expression due to methylation of the FMR1 promoter. Treatment of fragile X syndrome patients' lymphoblastoid cells with 5-azadeoxycytidine results in demethylation of the promoter and reactivation of the gene. The aim of the study was to analyze if methotrexate, an agent which also reduces DNA methylation but with less toxicity than 5-azadeoxycytidine, has therapeutic potential in fragile X syndrome.
Fibroblasts of fragile X syndrome patients were treated with methotrexate in concentrations ranging from 1 to 4 mug/ml for up to 14 days. FMR1 and FMRP expression were analyzed by quantitative PCR and western blotting.
FMR1 mRNA was detected and levels correlated positively with methotrexate concentrations and time of treatment, but western blotting did not show detectable FMRP levels.
We show that it is possible to reactivate FMR1 transcription in fibroblasts of fragile X syndrome patients by treatment with methotrexate. However, we were not able to show FMRP expression, possibly due to the reduced translation efficacy caused by the triplet repeat extension. Unless FMR1 reactivation is more effective in vivo our results indicate that methotrexate has no role in the treatment of fragile X syndrome.
Journal of Neurodevelopmental Disorders 09/2013; 5(1):23. · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background/Aims: In adults, plasma exchange (PE) has been shown to be an efficient treatment for severe relapses of acute inflammatory CNS demyelinating diseases. The aim of this study was to evaluate the safety and efficacy of this treatment in pediatric patients. Methods: We retrospectively analyzed a single-center cohort of pediatric patients with inflammatory CNS demyelinating disorders who underwent apheresis between 2007 and 2011. Results: Ten patients (mean age: 11.6 ± 3.4 years) with an acute relapse of multiple sclerosis (n = 5), neuromyelitis optica (n = 2) or acute disseminated encephalomyelitis were included. All received methylprednisolone prior to treatment with either PE (n = 5) or immunoadsorption (n = 5). Apheresis-related side effects were either self-limiting or easily managed. EDSS (Expanded Disability Status Scale) improved in 7 of 8 patients during apheresis and in all patients within 30 days from a median of 7.5 to 1 (p < 0.01). The visual acuity initially worsened during the procedure in 3 of 7 affected eyes (mean 0.09), but improved in all at follow-up (mean: 0.5; p = 0.008). Conclusions: Apheresis was well tolerated and associated with a favorable outcome in all pediatric patients similar to reports in adults.
[Show abstract][Hide abstract] ABSTRACT: To assess pediatric patients with multiple sclerosis (MS) for early signs of homeostatic and functional abnormalities in conventional (Tcon) and regulatory T cells (Treg).
We studied the composition of the peripheral T-cell compartment and Treg function in a cross-sectional study with 30 pediatric MS (pMS) patients by multicolor flow cytometry and proliferation assays. Data were compared to those obtained from adult patients (n = 26) and age-matched control donors (n = 67).
Proportions of naive T cells were 10%-20% higher in children than in adults, reflecting the age-related decline. pMS patients, however, had clearly lower numbers of naive T cells, among them recent thymic emigrants (RTE), whereas percentages of memory T cells were increased. In the Treg compartment, reduced RTE numbers coincided with markedly dampened suppressive capacities of total Treg. These homeostatic changes in circulating T cells precisely paralleled the pattern seen in adult MS. As in adults, treatment with immunomodulatory drugs attenuated these alterations.
The homeostatic changes detected in the T-cell compartment in pMS are similar to those in adult-onset disease. With ratios between naive and memory T-cell subsets matching those of 20- to 30-years-older controls, signs of early thymic involution are already found in pMS, suggesting that an intrinsic compromise in thymic-dependent T-cell neogenesis might contribute to MS pathogenesis.
[Show abstract][Hide abstract] ABSTRACT: Loss of folate receptor-α function is associated with cerebral folate transport deficiency and childhood-onset neurodegeneration. To clarify the mechanism of cerebral folate transport at the blood-cerebrospinal fluid barrier, we investigate the transport of 5-methyltetrahydrofolate in polarized cells. Here we identify folate receptor-α-positive intralumenal vesicles within multivesicular bodies and demonstrate the directional cotransport of human folate receptor-α, and labelled folate from the basolateral to the apical membrane in rat choroid plexus cells. Both the apical medium of folate receptor-α-transfected rat choroid plexus cells and human cerebrospinal fluid contain folate receptor-α-positive exosomes. Loss of folate receptor-α-expressing cerebrospinal fluid exosomes correlates with severely reduced 5-methyltetrahydrofolate concentration, corroborating the importance of the folate receptor-α-mediated folate transport in the cerebrospinal fluid. Intraventricular injections of folate receptor-α-positive and -negative exosomes into mouse brains demonstrate folate receptor-α-dependent delivery of exosomes into the brain parenchyma. Our results unravel a new pathway of folate receptor-α-dependent exosome-mediated folate delivery into the brain parenchyma and opens new avenues for cerebral drug targeting.
[Show abstract][Hide abstract] ABSTRACT: Diagnostic magnetic resonance imaging (MRI) criteria have not been sufficiently validated in pediatric multiple sclerosis (MS) despite differences in epidemiologic data and clinical disease courses between pediatric and adult MS.
The objective of this paper is to evaluate the diagnostic applicability and validity of the revised McDonald diagnostic criteria 2010 in a large cohort of pediatric-onset MS patients (POMS) and compare them to previously recommended MRI-based classifications. Furthermore, we aimed to investigate the contribution of spinal cord lesions to the revised McDonald criteria 2010.
A cohort of 85 patients with definite MS, age at onset 2.8-18 years, was analyzed in a retrospective multicenter study. Number and regional distribution of T2w and contrast-enhancing T1w lesions at initial and follow-up MRIs were main outcome measures.
In 62% of POMS the initial MRI within four weeks after symptom onset was sufficient to diagnose MS according to the revised McDonald criteria 2010. In a subcohort of patients with spinal MRI at first presentation, 10% reached the dissemination in space (DIS) and dissemination in time (DIT) criteria only by the inclusion of contrast-enhancing spinal lesions.
The revised McDonald criteria 2010 facilitate the diagnosis of POMS already at first presentation. The addition of a spinal cord MRI was helpful only in selected cases.
[Show abstract][Hide abstract] ABSTRACT: West syndrome (WS) is an epileptic encephalopathy of childhood, defined by the presence of clustered spasms usually occurring before the age of 1 year, hypsarrhythmia on EEG that is notoriously difficult to define, and developmental arrest or regression. The incidence of WS is 1:3200 live births with an aetiology-dependent prognosis. Up to 80% of children with symptomatic WS suffer from mental retardation, and approximately 50% develop Lennox-Gastaut syndrome. Using homozygosity mapping followed by exome sequencing, we identified a ADP-ribosylation factor (ARF) guanine nucleotide-exchange factor two (brefeldin A-inhibited) (ARFGEF2) mutation in five related infants with WS. ARFGEF2 is involved in the activation of ARFs by accelerating replacement of bound guanosine diphosphate (GDP) with Guanosine triphosphate (GTP), and is involved in Golgi transport. A mutation in ARFGEF2 has been previously described only once, causing microcephaly and periventricular heterotopia. Here, we describe a novel ARFGEF2 mutation in five related patients presenting with WS, microcephaly, periventricular heterotopia and thin corpus callosum.
Journal of Medical Genetics 06/2013; · 5.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In humans the concerted action of at least 13 different peroxisomal PEX proteins is needed for proper peroxisome biogenesis. Mutations in any of these PEX genes can lead to lethal neurometabolic disorders of the Zellweger syndrome spectrum (ZSS). Previously, we identified the W313G mutation located within the SH3 domain of the peroxisomal protein, PEX13. As this tryptophan residue is highly conserved in almost all known SH3 proteins, we investigated the pathogenic mechanism of the W313G mutation and its role in PEX13 interactions and functions in peroxisome biogenesis. Here, we report for the first time that human PEX13 interacts with itself in peroxisomes in living cells. We demonstrate that the import of PTS1 (peroxisomal targeting signal 1) proteins is specifically disrupted when homooligomerization of PEX13 is interrupted. Live cell FRET microscopy in living cells as well as co-immunoprecipitation experiments reveal that the highly conserved W313 residue is important for self-association of PEX13 but is not required for interaction with PEX14, a well established interaction partner at the peroxisomal membrane. Experiments with truncated constructs indicate that although the W313G mutation resides in the C-terminal SH3 domain, the N-terminal half is necessary for peroxisomal localization, which in turn appears to be crucial for homooligomerization. Furthermore, rescue of homooligomerization in the W313G mutant cells through complementation with truncation constructs restores import of peroxisomal matrix proteins. Taken together, the thorough analyses of a ZSS patient mutation unraveled the general cell biological function of PEX13 and its mechanism in the import of peroxisomal matrix PTS1 proteins.
Human Molecular Genetics 05/2013; · 7.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Terminal deletions of chromosome 3p26.3 confined to the CHL1 gene have previously been described in children with intellectual disability and epilepsy. Here, we report for the first time, a 3p26.3 duplication including only the CHL1 gene in an intellectually disabled girl with epilepsy. The penetrance of both deletions and duplications in 3p26.3 is reduced because all chromosomal imbalances were inherited from healthy parents. Further studies are needed to specify the pathogenic mechanism of 3p26.3 imbalances and to estimate recurrence risks in genetic counseling. However, the description of both deletions and duplications of chromosome 3p26.3 in nonsyndromic intellectual disability suggests that CHL1 is a dosage-sensitive gene with an important role for normal cognitive development.
[Show abstract][Hide abstract] ABSTRACT: Multiple sulfatase deficiency (MSD) is a rare inborn error of metabolism affecting posttranslational activation of sulfatases by the formylglycine generating enzyme (FGE). Due to mutations in the encoding SUMF1 gene, FGE's catalytic capacity is impaired resulting in reduced cellular sulfatase activities. Both, FGE protein stability and residual activity determine disease severity and have previously been correlated with the clinical MSD phenotype. Here, we report a patient with a late infantile severe course of disease. The patient is compound heterozygous for two so far undescribed SUMF1 mutations, c.156delC (p.C52fsX57) and c.390A>T (p.E130D). In patient fibroblasts, mRNA of the frameshift allele is undetectable. In contrast, the allele encoding FGE-E130D is expressed. FGE-E130D correctly localizes to the endoplasmic reticulum and has a very high residual molecular activity in vitro (55% of wildtype FGE); however, it is rapidly degraded. Thus, despite substantial residual enzyme activity, protein instability determines disease severity, which highlights that potential MSD treatment approaches should target protein folding and stabilization mechanisms.European Journal of Human Genetics advance online publication, 16 January 2013; doi:10.1038/ejhg.2012.291.
European journal of human genetics: EJHG 01/2013; · 3.56 Impact Factor