Novel subtype of mucopolysaccharidosis caused by arylsulfatase K (ARSK) deficiency

BackgroundMucopolysaccharidoses (MPS) are monogenic metabolic disorders that significantly affect the skeleton. Eleven enzyme defects in the lysosomal degradation of glycosaminoglycans (GAGs) have been assigned to the known MPS subtypes (I–IX). Arylsulfatase K (ARSK) is a recently characterised lysosomal hydrolase involved in GAG degradation that removes the 2-O-sulfate group from 2-sulfoglucuronate. Knockout of Arsk in mice was consistent with mild storage pathology, but no human phenotype has yet been described.MethodsIn this study, we report four affected individuals of two unrelated consanguineous families with homozygous variants c.250C>T, p.(Arg84Cys) and c.560T>A, p.(Leu187Ter) in ARSK, respectively. Functional consequences of the two ARSK variants were assessed by mutation-specific ARSK constructs derived by site-directed mutagenesis, which were ectopically expressed in HT1080 cells. Urinary GAG excretion was analysed by dimethylene blue and electrophoresis, as well as liquid chromatography/mass spectrometry (LC-MS)/MS analysis.ResultsThe phenotypes of the affected individuals include MPS features, such as short stature, coarse facial features and dysostosis multiplex. Reverse phenotyping in two of the four individuals revealed additional cardiac and ophthalmological abnormalities. Mild elevation of dermatan sulfate was detected in the two subjects investigated by LC-MS/MS. Human HT1080 cells expressing the ARSK-Leu187Ter construct exhibited absent protein levels by western blot, and cells with the ARSK-Arg84Cys construct showed markedly reduced enzyme activity in an ARSK-specific enzymatic assay against 2-O-sulfoglucuronate-containing disaccharides as analysed by C18-reversed-phase chromatography followed by MS.ConclusionOur work provides a detailed clinical and molecular characterisation of a novel subtype of mucopolysaccharidosis, which we suggest to designate subtype X.

MO113CALCULATED URINARY CALCIUM-OXALATE SATURATION (ßCAOX) IS NOT SPECIFICALLY ELEVATED IN PATIENTS WITH PRIMARY HYPEROXALURIA

Background and Aims In the primary hyperoxalurias (PH; types 1-3) recurrent urolithiasis (UL) and/or progressive nephrocalcinosis (NC) are the clinical hallmarks. Three different enzyme defects lead to endogenous oxalate overproduction and to extremely elevated urinary oxalate excretion (UOx). Thus, it seems logical that urine is supersaturated for calcium-oxalate (CaOx). It was, hence, speculated that urinary CaOx saturation (ßCaOx), calculated by computed programs, is significantly higher as compared to that of patients with idiopathic CaOx stones. We now aimed to evaluate and calculate urinary ßCaOx in PH patients according to type, as well as in non-PH patients with UL or NC. Method The computed equilibrium program EQUIL2 was used for the calculation of ßCaOx. For this, 24 h urine specimen of 70 patients with non-PH NC (46 male, 24 female, median age 6.06 (range 0.3-31.4 years)), of 149 idiopathic CaOx UL (90/59 m/f, age 8.5 (0.1-68.6)), of 51 PH 1 patients (31/21, age 12.33 (0.8-63.8)), of 5 PH 2 patients (3/2, age 5.41 (4.3-12.9)) and of 14 PH 3 patients (8/6, age 8.5 (2.9-29.3)) were analyzed for all necessary components. All patients were in stable kidney function (eGFR > 45 ml/min). Results Uox was higher in the PH patients as compared to the non-PH UL or NC patients (p < 0.05). However, there was no statistical difference between the Uox in PH 1 vs PH 2 or PH 3 patients, although, a clear effect of B6 medication was visible in PH1 patients. Urinary calcium excretion was lower (not significant) in PH patients as compared to NC/UL. There was no difference in ßCaOx when PH were compared to non-PH patients and it mostly remained in the normal range. Conclusion Urine ßCaOx is similar in PH and non-PH stone formers. Therefore, calculation of ßCaOx using computed programs is not a reliable parameter to define the definitively extreme CaOx supersaturation of urine from PH patients. This miscalculation is related to a rather lowish urinary calcium excretion in PH as compared to other UL/NC patients. Therefore, we recommend not to use such programs to express the risk of recurrent stone disease or nephrocalcinosis in PH.

Clinical and genetic profile of patients with primary hyperoxaluria: observation from a single centre from West India

Background: Primary hyperoxaluria (PH) is characterized by oxalate overproduction due to glyoxylate pathway enzyme defects in the liver. Apart from heterogeneous clinical manifestations of PH, diagnosis by urinary and plasma oxalate levels or stone analysis is not always confirmatory. Mutational analysis is required for definite diagnosis. There is heterogeneity between genotype of PH patients between Western and Indian population. The aim of this study is to describe clinical and genetic profile of Indian patients, diagnosed with PH in Western India.Methods: All clinical PH suspects in Nephrology and Paediatric Nephrology units from October 2016-September 2020, were counselled for genetic analysis for diagnostic confirmation. Cases, genetically confirmed to have PH, were included and retrospectively analysed for their clinical profile, modality of renal replacement therapy, survival/death. The mutations identified in our patients were compared with commonly prevalent mutations in world PH databases.Results: 13 of 15 patients were identified to have genetically confirmed PH. Median age at diagnosis was 1 year (range, 4 months to 46 years) and six (46.15%) were male. Six (46.15%) infants, two (15.38%) adolescents and five (38.46%) presented in adulthood. Nine presented as ESKD, while three patients progressed to ESKD during study. Eight (61.54%) with AGXT mutation were diagnosed as PH type1, four (30.76%) GRHPR mutation while one (7.69%) female infant had PH type 3 with HOGA mutation. Out of thirteen, five (38.46%) patients expired, five (38.46%) are ESKD requiring dialysis. Two (15.38%) post-transplant patients, graft loss for one and another requiring supportive medical management for deteriorating eGFR.Conclusions: ESKD being commonest presentation, high index of suspicion in all cases with renal stone and complete work up should be done for early diagnosis and timely intervention. National registry is required for detection of novel PH mutations in Indian population.

7. Enzymes and disease

‘Enzymes and disease’ assesses how, in relation to medical science, enzymes may be the problem or they might offer the solution. What happens if enzymes are faulty in some way? Enzyme defects lead to diseases such as alkaptonuria, phenylketonuria, Sudden Infant Death Syndrome (SIDS), and Jamaican Vomiting Sickness. On the other hand, there are often situations in which humans deliberately seek to damp down the activity of normally functioning enzymes in human bodies, and this is how many drugs work. Enzymes, human or otherwise, are also nowadays widely used as agents for diagnosis or therapy.

Inherited Disorders of Lysine Metabolism: A Review

ABSTRACT Lysine is an essential amino acid, and inherited diseases of its metabolism therefore represent defects of lysine catabolism. Although some of these enzyme defects are not well described yet, glutaric aciduria type I (GA1) and antiquitin (2-aminoadipic-6-semialdehyde dehydrogenase) deficiency represent the most well-characterized diseases. GA1 is an autosomal recessive disorder due to a deficiency of glutaryl-CoA dehydrogenase. Untreated patients exhibit early onset macrocephaly and may present a neurological deterioration with regression and movement disorder at the time of a presumably “benign” infection most often during the first year of life. This is associated with a characteristic neuroimaging pattern with frontotemporal atrophy and striatal injuries. Diagnosis relies on the identification of glutaric and 3-hydroxyglutaric acid in urine along with plasma glutarylcarnitine. Treatment consists of a low-lysine diet aiming at reducing the putatively neurotoxic glutaric and 3-hydroxyglutaric acids. Additional therapeutic measures include administration of l-carnitine associated with emergency measures at the time of intercurrent illnesses aiming at preventing brain injury. Early treated (ideally through newborn screening) patients exhibit a favorable long-term neurocognitive outcome, whereas late-treated or untreated patients may present severe neurocognitive irreversible disabilities. Antiquitin deficiency is the most common form of pyridoxine-dependent epilepsy. α-Aminoadipic acid semialdehyde (AASA) and Δ-1-piperideine-6-carboxylate (P6C) accumulate proximal to the enzymatic block. P6C forms a complex with pyridoxal phosphate (PLP), a key vitamer of pyridoxine, thereby reducing PLP bioavailability and subsequently causing epilepsy. Urinary AASA is a biomarker of antiquitin deficiency. Despite seizure control, only 25% of the pyridoxine-treated patients show normal neurodevelopment. Low-lysine diet and arginine supplementation are proposed in some patients with decrease of AASA, but the impact on neurodevelopment is unclear. In summary, GA1 and antiquitin deficiency are the 2 main human defects of lysine catabolism. Both include neurological impairment. Lysine dietary restriction is a key therapy for GA1, whereas its benefits in antiquitin deficiency appear less clear.

Management of Children with Glycogen Storage Disease (Liver Involvement Forms). Best Practice Guidelines

Glycogen storage disease is the hereditary carbohydrate metabolism pathology which is caused by mutations in various genes encoding enzymes responsible for glycogenesis and glycogenolysis. Excessive glycogen deposition in various tissues cells (mostly in liver and muscles) occurs due to enzyme defects. The authors present recent epidemiological data and features of glycogen storage disease etiology and pathogenesis. Clinical characteristics of different types of this disease are also presented. The data on laboratory-instrumental and morphological signs of glycogen storage disease in children, as well as data on its treatment methods is provided in accordance with the developed clinical guidelines. The article provides relevant information on disease types with predominant liver involvement, besides the variety of clinical forms of glycogenosis.

The Significance of Mitochondrial Dysfunction in Cancer

As an essential organelle in nucleated eukaryotic cells, mitochondria play a central role in energy metabolism, maintenance of redox balance, and regulation of apoptosis. Mitochondrial dysfunction, either due to the TCA cycle enzyme defects, mitochondrial DNA genetic mutations, defective mitochondrial electron transport chain, oxidative stress, or aberrant oncogene and tumor suppressor signaling, has been observed in a wide spectrum of human cancers. In this review, we summarize mitochondrial dysfunction induced by these alterations that promote human cancers.

The Role of Hematopoietic Cell Transplant in the Glycoprotein Diseases

The glycoprotein disorders are a group of lysosomal storage diseases (α-mannosidosis, aspartylglucosaminuria, β-mannosidosis, fucosidosis, galactosialidosis, sialidosis, mucolipidosis II, mucolipidosis III, and Schindler Disease) characterized by specific lysosomal enzyme defects and resultant buildup of undegraded glycoprotein substrates. This buildup causes a multitude of abnormalities in patients including skeletal dysplasia, inflammation, ocular abnormalities, liver and spleen enlargement, myoclonus, ataxia, psychomotor delay, and mild to severe neurodegeneration. Pharmacological treatment options exist through enzyme replacement therapy (ERT) for a few, but therapies for this group of disorders is largely lacking. Hematopoietic cell transplant (HCT) has been explored as a potential therapeutic option for many of these disorders, as HCT introduces functional enzyme-producing cells into the bone marrow and blood along with the engraftment of healthy donor cells in the central nervous system (presumably as brain macrophages or a type of microglial cell). The outcome of HCT varies widely by disease type. We report our institutional experience with HCT as well as a review of the literature to better understand HCT and outcomes for the glycoprotein disorders.