Charakterisierung einer neuen SLC35A1-Mutation bei einer Patientin mit Glykosylierungs- und Stoffwechseldefiziten

Die Glykosylierung ist eine wichtige co- und posttranslationale Modifikation von Proteinen, die für deren korrekte Faltung, Funktionalität und Interaktionen benötigt wird. Wird dieser Prozess durch Mutationen im Gen eines der beteiligten Proteine beeinträchtigt, führt dies zu einer seltenen Stoffwechselkrankheit, die als „Congenital Disorders of Glycosylation“ (CDG) bezeichnet wird. Der sehr seltene CDG-Typ SLC35A1-CDG wird durch einen Defekt des SLC35A1-Proteins hervorgerufen, das als Sialinsäuretransporter dafür verantwortlich ist, CMP-Sialinsäure vom Cytosol ins Golgi-Lumen zu transportieren. Bisher waren nur fünf SLC35A1-CDG Patienten bekannt, die Symptome wie neurologische Defizite und Gerinnungsstörungen aufwiesen. Im Rahmen dieser Arbeit wurde die c.133A>G (p.Thr45Ala) Mutation im SLC35A1 Gen einer weiteren Patientin charakterisiert, die unter anderem an einer allgemeinen Gedeihstörung, Mikrozephalie, Thrombozytopenie sowie Neutropenie leidet. Anhand einer in silico Analyse wurde zunächst ermittelt, dass die Mutation pathogene Eigenschaften, aber möglicherweise eher milde Auswirkungen auf die Funktionalität des Proteins haben könnte. Um die Mutation unabhängig vom genetischen Hintergrund der Patientin zu untersuchen, wurde eine HEK293 SLC35A1 Knock-out-Zelllinie mittels CRISPR/Cas9 generiert, durch die festgestellt werden konnte, dass das mutierte SLC35A1-Protein generell noch funktionsfähig war, aber eine verkürzte Halbwertszeit aufwies. In Fibroblasten lokalisierte es ordnungsgemäß im Golgi-Apparat, aber zeigte eine leicht reduzierte Aktivität, die möglicherweise auf die verringerte Stabilität zurückzuführen war. In den Fibroblasten der Patientin wurde neben einer leichten Störung der O-Glykosylierung eine stark beeinträchtigte N-Glykosylierung sowie eine reduzierte α-2,3 Sialylierung festgestellt. Im Serum der Patientin waren dagegen kaum Glykosylierungsdefizite vorhanden, was auf organspezifische Unterschiede in der Bereitstellung von Sialinsäure für die Glykosylierungsprozesse hindeuten könnte. Durch transkriptomische und proteomische Analysen wurden Beeinträchtigungen weiterer Glykosylierungsprozesse, der O-GlcNAcylierung und C-Mannosylierung, in den Patientenfibroblasten entdeckt, sowie die Deregulation verschiedener Bereiche der N-Glykosylierung, die teilweise in direktem Zusammenhang mit einem SLC35A1-Defekt zu stehen scheinen. Auch die Lipidhomöostase war in den Zellen der Patientin verändert und es gab Hinweise auf eine Beeinträchtigung von grundlegenden zellulären Funktionen sowie dem Energiemetabolismus. Die beobachtete, verminderte Proliferation der Patientenfibroblasten konnte durch Supplementation mit GlcNAc verbessert werden, nicht jedoch die Glykosylierungsdefizienz, weshalb dieser Phänotyp vermutlich auf Probleme im Metabolismus zurückzuführen war. Ein Komplementierungsversuch der Patientenzellen mit dem wildtypischen SLC35A1-Gen konnte den Glykosylierungsdefekt nur teilweise beheben, weshalb auch der individuelle genetische Hintergrund der Patientin zu den beobachteten Defiziten beitragen könnte. Letztendlich scheint die SLC35A1 c.133A>G Mutation zu einer eher milden Form von SLC35A1-CDG zu führen, die vermutlich hauptsächlich auf die reduzierte Stabilität des mutierten Proteins zurückzuführen ist

International consensus guidelines for phosphoglucomutase 1 deficiency (PGM1-CDG): Diagnosis, follow-up, and management

P. W. is supported by the Clinical Research Fund, University Hospitals Leuven, Leuven, Belgium. This work is partially funded by the grant titled Frontiers in Congenital Disorders of Glycosylation (1U54NS115198-01) from the National Institute of Neurological Diseases and Stroke (NINDS), the National Center for Advancing Translational Sciences (NCATS), and the Rare Disorders Consortium Research Network (RDCRN) (E. M., K. R., C. F., H. F., C. L., and A. E.)Phosphoglucomutase 1 (PGM1) deficiency is a rare genetic disorder that affects glycogen metabolism, glycolysis, and protein glycosylation. Previously known as GSD XIV, it was recently reclassified as a congenital disorder of glycosylation, PGM1-CDG. PGM1-CDG usually manifests as a multisystem disease. Most patients present as infants with cleft palate, liver function abnormalities and hypoglycemia, but some patients present in adulthood with isolated muscle involvement. Some patients develop life-threatening cardiomyopathy. Unlike most other CDG, PGM1-CDG has an effective treatment option, d-galactose, which has been shown to improve many of the patients' symptoms. Therefore, early diagnosis and initiation of treatment for PGM1-CDG patients are crucial decisions. In this article, our group of international experts suggests diagnostic, follow-up, and management guidelines for PGM1-CDG. These guidelines are based on the best available evidence-based data and experts' opinions aiming to provide a practical resource for health care providers to facilitate successful diagnosis and optimal management of PGM1-CDG patients.preprintpublishe

A Randomized Controlled ERP Study on the Effects of Multi-Domain Cognitive Training and Task Difficulty on Task Switching Performance in Older Adults

Executive functions are subject to a marked age-related decline, but have been shown to benefit from cognitive training interventions. As of yet, it is, however, still relatively unclear which neural mechanism can mediate training-related performance gains. In the present electrophysiological study, we examined the effects of multi-domain cognitive training on performance in an untrained cue-based task switch paradigm featuring Stroop color words: participants either had to indicate the word meaning of Stroop stimuli (word task) or perform the more difficult task of color naming (color task). One-hundred and three older adults (>65 years old) were randomly assigned to a training group receiving a 4-month multi-domain cognitive training, a passive no-contact control group or an active (social) control group receiving a 4-month relaxation training. For all groups, we recorded performance and EEG measures before and after the intervention. For the cognitive training group, but not for the two control groups, we observed an increase in response accuracy at posttest, irrespective of task and trial type. No training-related effects on reaction times were found. Cognitive training was also associated with an overall increase in N2 amplitude and a decrease of P2 latency on single trials. Training-related performance gains were thus likely mediated by an enhancement of response selection and improved access to relevant stimulus-response mappings. Additionally, cognitive training was associated with an amplitude decrease in the time window of the target-locked P3 at fronto-central electrodes. An increase in the switch positivity during advance task preparation emerged after both cognitive and relaxation training. Training-related behavioral and event-related potential (ERP) effects were not modulated by task difficulty. The data suggest that cognitive training increased slow negative potentials during target processing which enhanced the N2 and reduced a subsequent P3-like component on both switch and non-switch trials and irrespective of task difficulty. Our findings further corroborate the effectiveness of multi-domain cognitive training in older adults and indicate that ERPs can be instrumental in uncovering the neural processes underlying training-related performance gains

A Comparison of the Effects of Short-Term Physical and Combined Multi-Modal Training on Cognitive Functions

Physical training has beneficial effects not only on physical fitness, but also on cognitive functions. The most effective way to improve cognitive functions via physical training as well as the degree to which training effects transfer to untrained cognitive functions is still unclear, however. Here, we investigated the effects of adaptive and multi-modal short-term training interventions on cognitive training gains and transfer effects. Over a period of 12 weeks, 102 employees of a car manufacturing company (age range 20 to 61 years) received trainer-guided exercises, consisting of either two adaptive training interventions, physical (strength) training and multi-modal (motor–cognitive) training, or non-adaptive strength training (active control group). For the multi-modal intervention, the “Agility Board” was employed, a novel, multi-modal training device. Pre- and post-training, psychometric tests were conducted to measure cognitive abilities, such as perceptual speed, attention, short-term memory, working memory, inhibition, and mental rotation. In addition, motor–cognitive performance was assessed. Compared with the active control group, both training groups showed enhanced performance at posttest. While multi-modal training yielded performance improvements only in trained tasks, physical training was associated with improvements in untrained working memory updating and immediate recall tasks, suggesting transfer effects to short-term and working memory functioning. In summary, the results demonstrate the importance of adaptive difficulty settings for short-term physical training interventions, at least for the enhancement of working memory

Congenital disorders of glycosylation with defective fucosylation

Fucosylation is essential for intercellular and intracellular recognition, cell-cell interaction, fertilization, and inflammatory processes. Only five types of congenital disorders of glycosylation (CDG) related to an impaired fucosylation have been described to date: FUT8-CDG, FCSK-CDG, POFUT1-CDG SLC35C1-CDG, and the only recently described GFUS-CDG. This review summarizes the clinical findings of all hitherto known 25 patients affected with those defects with regard to their pathophysiology and genotype. In addition, we describe five new patients with novel variants in the SLC35C1 gene. Furthermore, we discuss the efficacy of fucose therapy approaches within the different defects