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Introduction: Autosomal recessive polycystic kidney disease (ARPKD) is a rare inherited disease, affecting both the kidneys and the liver. It may cause congenital hepatic fibrosis (CHF), leading to portal hypertension and its complications with a need of liver transplantation. A transjugular intrahepatic portosystemic shunt (TIPSS) could serve as a treatment for portal hypertension in these children. This is a minimally invasive endovascular technique of portosystemic shunting, however data about its use in children are scarce. Materials and methods: We report on 5 children with CHF that underwent a TIPSS placement in our center and compare them to other similar patients described in the literature. We studied the effect of TIPSS placement on portal hypertension, liver and kidney function and we monitored for long term complications. Results: At the end of follow-up we noticed a significant reduction of spleen size (18.1cm to 14.9cm) and a trend for reduction of hypersplenism with a rise in platelet count (100 x10^9/L to 145.5 x10^9/L). Esophageal varices and ascites disappeared in all patients. Liver and kidney function remained stable. One patient had an infection and stenosis of the stent. There were no other long term complications. Conclusion: Overall we can conclude that TIPSS is a feasible and safe alternative for surgical shunting in children with CHF, also on the long term. It is an effective treatment for portal hypertension and can postpone the need for a liver transplantation.

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Introductie Hypophosphatasie (HPP) is een autosomaal dominante of recessieve skeletale aandoening veroorzaakt door een loss-of-function mutatie in het gen dat codeert voor niet-weefselspecifieke alkalische fosfatase (TNSALP). Er zijn op heden 355 mutaties gekend met verschillende penetrantie. De residuele enzymactiviteit van alkalische fosfatase (ALP) bepaalt de ernst van de aandoening waardoor HPP het breedste klinisch spectrum van alle skeletale aandoeningen kent. Verlaagde activiteit van ALP is de biochemische hallmark, maar dit wordt niet als afwijkend weergegeven door het laboratorium. Naast HPP kent laag ALP een niet exhaustieve lijst van differentieel diagnostiek. Materiaal en methoden In een periode van vijf jaar op de afdeling Kindergeneeskunde van een tertiair centrum werden 701 patiënten met uitsluitend verlaagde ALP waarden geïdentificeerd. We beschrijven de klinische presentatie in een subgroep van 191 patiënten met consistent laag serum ALP. Resultaten 27,7% heeft slechts 1 verlaagde waarde. Binnen de subgroep met minstens 2 verlaagde waarden (27,2%) vinden we 2 patiënten (1%) met HPP en 117 patiënten (61%) met secundaire HPP. Patiënten met onduidelijke diagnose zowel met als zonder verdachte symptomen zullen verder worden nagekeken. Conclusie Er is een interessant tijdsperk aangebroken sinds behandeling voor HPP beschikbaar is. Doch blijft diagnostiek moeilijk omwille van geen automatische melding van laag ALP en breed klinisch spectrum. Implementatie van geslachts- en leeftijdsspecifieke ondergrenswaarden van ALP in de dagelijkse kliniek is essentieel voor diagnose van HPP na uitsluiten van secundaire HPP.

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he mitochondrial oxidative phosphorylation system (OXPHOS) generates most of the cellular energy in the form of ATP. Pathogenic variants in genes crucial for mitochondrial function cause primary mitochondrial diseases (PMD). PMD form a large, heterogeneous group of disorders that affect at least 1 in 5000 individuals. Patients may present at any age, with symptoms in any organ, at any severity. Due to the diversity in clinical presentation and the lack of a single clear biochemical profile, diagnosis of PMD remains a challenge. Most PMD have a poor prognosis and lack effective therapies. There is thus a need for the development of specific, sensitive and rapid diagnostic markers, and for the discovery of effective therapeutic interventions.We hypothesised that PMD causes important metabolic changes due to the key role of mitochondria in numerous biochemical pathways. This project aimed to understand the cellular metabolic re-wiring occurring in PMD by characterising the metabolic consequences of OXPHOS dysfunction in skin fibroblasts derived from patients with PMD and healthy controls. The objectives were 3-fold: first to develop a new diagnostic technique, second to unravel the cellular profile in OXPHOS dysfunction, and third, to identify and test novel treatment strategies. First, the potential of oxygraphy as a diagnostic tool for PMD was investigated and compared to the gold standard of enzymology. The results showed that oxygraphy is a powerful new tool for the biochemical detection of PMD. However, oxygraphy and enzymology are complementary techniques, and should ideally be combined. The biochemical results must also be interpreted in regard to the clinical presentation, the other investigations already performed, and genetic testing results. Second, the metabolic profile of OXPHOS dysfunction was described in skin-derived fibroblasts obtained from patients with diverse PMD and validated in pharmacological models of OXPHOS dysfunction. Growth rate was determined using the Incucyte technology and steady-state glucose and glutamine tracing studies were performed with LC-MS quantification of cellular metabolites. Our results revealed that OXPHOS deficiency causes a proliferation defect and is associated with a distinct metabolic profile. The main features of this signature are a depletion of aspartic acid, of TCA intermediates and increased levels of glycerol-3-phosphate. This profile seems to be related to an NAD+/NADH imbalance. Finally, the therapeutic potential of numerous nutritional supplements was tested by assessing their effect on proliferation and on the metabolomics profile. In fibroblasts, therapy with pyruvate and uridine rescued the metabolic signature of OXPHOS dysfunction and the subsequent proliferation defect. Additionally, in zebrafish, pyruvate and uridine treatment increased the survival after rotenone exposure. This project highlights the importance of the NAD+/NADH imbalance following OXPHOS dysfunction and opens the door to novel diagnostic techniques and therapeutic interventions for PMD.

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Methylmalonic acidemia (MA) and propionic acidemia (PA) are inherited disorders in the propionate catabolism of the mitochondria, which result in the accumulation of organic acids in body fluids. The build-up of these organic acids may cause severe organ damage and complications such as neurodevelopmental delay, renal failure and cardiomyopathy. Therapy consists of a protein-restricted diet with L-carnitine supplements and a liver transplantation in case of severe phenotype or recurrent metabolic decompensations. Both non-transplanted and transplanted patients are monitored lifelong by a metabolic team to avoid organ damage and long-term complications. To improve the diagnosis and follow-up of these patients in the university hospital of Leuven, we have developed a rapid, state-of-the-art liquid chromatography tandem mass spectrometry (LC-MSMS) assay to quantify organic acids methylmalonic acid (MMA) and methylcitric acid (MCA) in plasma of patients. Plasma samples were prepared using protein precipitation and phospholipid removal plates to improve extraction and the method’s sensitivity. The assay was fully validated and met most of the predetermined criteria of the U.S. Food and Drug Administration (FDA). The concentration range of the linear calibration curve for MMA was 0.20-1,000 µmol/l and for MCA 2-1,000 µmol/l, respectively. The coefficient of variation (CV) of the between-run precision ranged from 5 % to 8 % and the CV of the within-run precision was ≤ 5 %. However, the method did not meet the criteria of carry-over (< 0.1 %) and process-efficiency (CV < 15 %). The assay showed 0.2 % carry-over for MMA at the highest calibration standard and the CV of the process-efficiency for MCA was 16 % at the highest spiking concentration. Therefore, the method should be further validated before it is used in the clinic. The assay was proven to be suitable for the diagnosis and monitoring of both non-transplanted and transplanted patients with MA and PA. The MMA and MCA concentration could be successfully determined in plasma samples of 20 patients. In two transplanted patients, plasma samples before and after transplantation were analyzed. Within one year, their MMA and MCA concentration decreased on average by 90 % and 75 % but still remained above the normal physiological concentration, which confirms the results of previous research of Maines et al. (1). In summary, we have developed a LC-MSMS assay for the diagnosis and follow-up of patients with MA and PA, which can be implemented in the lab routine of the department of Laboratory Medicine at the university hospital of Leuven. Because the method did not meet all validation criteria, the assay should be revalidated with more suitable calibration curves and more organized lab work before it is utilized in the lab.