Enzyme Defect Research Articles

Converging Roles of the Metal Transporter SMF11 and the Ferric Reductase FRE1 in Iron Homeostasis of Candida albicans.

Pathogenic fungi must appropriately sense the host availability of essential metals such as Fe. In Candida albicans and other yeasts, sensing of Fe involves mitochondrial Fe-S clusters. Yeast mutants for Fe-S cluster assembly sense Fe limitation even when Fe is abundant and hyperaccumulate Fe. We observe this same disrupted Fe sensing with C. albicans mutants of SMF11, a NRAMP transporter of divalent metals. Mutants of smf11 hyperaccumulate both Mn and Fe and the elevated Mn is secondary to Fe overload. As with Fe-S biogenesis mutants, smf11∆/∆ mutants show upregulation of ferric reductases that are normally repressed under high Fe, and Fe import is activated. However, unlike Fe-S biogenesis mutants, smf11∆/∆ mutants show no defects in mitochondrial Fe-S enzymes. Intriguingly, this exact condition of disrupted Fe sensing without inhibiting Fe-S clusters occurs with C. albicans fre1∆/∆ mutants encoding a ferric reductase. Mutants of fre1 and smf11 display similar perturbations in the cell wall, in filamentation and in the ROS burst of morphogenesis, a Fe-dependent process. As with FRE1, SMF11 is important for virulence in a mouse model for disseminated candidiasis. We propose a model in which FRE1 and SMF11 operate outside the mitochondrial Fe-S pathway to donate ferrous Fe for Fe sensing.

Whole Blood Transcriptome Analysis in Congenital Anemia Patients.

Congenital anemias include a broad range of disorders marked by inherent abnormalities in red blood cells. These abnormalities include enzymatic, membrane, and congenital defects in erythropoiesis, as well as hemoglobinopathies such as sickle cell disease and thalassemia. These conditions range in presentation from asymptomatic cases to those requiring frequent blood transfusions, exhibiting phenotypic heterogeneity and different degrees of severity. Despite understanding their different etiologies, all of them have a common pathophysiological origin with congenital defects of erythropoiesis. We can find different types, from congenital sideroblastic anemia (CSA), which is a bone marrow failure anemia, to hemoglobinopathies as sickle cell disease and thalassemia, with a higher prevalence and clinical impact. Recent efforts have focused on understanding erythropoiesis dysfunction in these anemias but, so far, deep gene sequencing analysis comparing all of them has not been performed. Our study used Quant 3' mRNA-Sequencing to compare transcriptomic profiles of four sickle cell disease patients, ten thalassemia patients, and one rare case of SLC25A38 CSA. Our results showed clear differentiated gene map expressions in all of them with respect to healthy controls. Our study reveals that genes related to metabolic processes, membrane genes, and erythropoiesis are upregulated with respect to healthy controls in all pathologies studied except in the SLC25A38 CSA patient, who shows a unique gene expression pattern compared to the rest of the congenital anemias studied. Our analysis is the first that compares gene expression patterns across different congenital anemias to provide a broad spectrum of genes that could have clinical relevance in these pathologies.

Nitisinone attenuates progression of aortic stenosis in patients with alkaptonuria: an analysis of the SONIA 2 study

Abstract Background/introduction Alkaptonuria (AKU) is a rare metabolic disorder caused by a defective enzyme, resulting in deposition of unmetabolised homogentisic acid in various connective tissues throughout the body (also termed "ochronosis"). Ochronosis of the aortic valve leading to progressive aortic stenosis is a rare but serious complication. Nitisinone decreases urinary and serum homogentisic acid levels and has been shown to improve morbidity and slow disease progression in AKU but the effects of this treatment on the progression of aortic stenosis have not yet been described. This review extrapolated from the data set of the SONIA 2 study, a 4-year multi-centre, randomised controlled trial investigating the effect of nitisinone on a composite clinical measure of AKU disease activity, but looked more specifically at measures of aortic stenosis disease progression. Methods Data was obtained from echocardiograms performed on 138 patients at baseline, 12, 24, 36 and 48 months of follow-up. In measuring the degree of aortic stenosis, the peak trans-aortic velocity (Vmax) was examined. A linear mixed effects regression model was used to assess the association between treatment and Vmax and to ascertain the difference in this measure at baseline and 48 months between the treatment and control groups. The mixed effects model incorporated both fixed effects for population parameters (age, sex, baseline Vmax, follow-up time) and treatment; and random effects, to account for intra-subject correlation of longitudinal observations of Vmax, inter-subject variability of baseline measurements of Vmax, and centre. Results At baseline, 19/138 patients (13.8%) had aortic stenosis, as classified by echocardiogram findings in accordance with the European Society of Cardiology (ESC) guidance on valvular heart disease, with 9/19 having mild aortic stenosis, 6/19 having moderate aortic stenosis and 4/19 having severe aortic stenosis. 25/138 had aortic sclerosis (see figure 1). The prevalence of aortic valve disease increased with age. From the 4-year follow-up period, 613 longitudinal observations of 138 subjects across all sites were obtained. At baseline, the difference in Vmax between the control and treatment groups was 0.063 m/s [95% CI: -0.054 m/s to 0.18 m/s] and did not reach statistical significance (p=0.23). At the end of the 4-year treatment period, the difference in Vmax was 0.10 m/s [95% CI: -0.0007 m/s to 0.20 m/s] and was statistically significant (p=0.05) (see figure 2). Conclusion Nitisinone slowed progression of aortic stenosis in patients with AKU. This may be grounds for timely initiation of nitisinone in those deemed to be at high risk, as identified by echocardiography. Of note, this is the first time that any medical therapy has ever been shown to affect the natural history of aortic stenosis.

6664 A Case of Undistinguished Congenital Adrenal Hyperplasiain a Patient with Hypertensive Emergency and Hypokalemia

Abstract Disclosure: V.L. Del Signore: None. S.T. Kaufman: None. CAH is a group of autosomal recessive disorders resulting in alterations of adrenal steroid biosynthesis. With 95% of CAH cases due to 21-hydroxylase deficiency; other causes are rare. The metabolic, phenotypic, and physiologic derangements are specific to the altered enzymatic pathways, most of which are life threatening. Identifying the enzymatic defect is crucial to treat the patient. We present a case of undifferentiated CAH in an adult resulting in significant systemic illness. A 26-year-old well virilized male presented with chief complaint of shortness of breath, lower extremity swelling, and abdominal distension for 3 weeks. He was found to have acute decompensated heart failure with LVEF 20-25%, NSTEMI, atrial fibrillation, hypertensive emergency with BP of 224/102, and potassium (K+) of 2.7 (3.5-5mmol/L). PMH included hypertension and CAH diagnosed at birth. Patient was unsure of his CAH defect. Pediatric endocrinology prescribed glucocorticoids until age 17 at which point he was told steroids were no longer required. He had been lost to follow up for 9 years. Pediatric records were unattainable. Patient remained hypokalemic and hypertensive despite aggressive K+ repletion and multiple IV antihypertensives. Endocrine work up revealed renin 0.19 (0.25- 5.82ng/mL/hr), aldosterone 4 (< or = 21ng/dL), DHEAs 97 (74-617ug/dL), FSH <0.3 (1.4 - 18.1 m[IU]/mL), LH <0.3 (1.5 - 9.3 m[IU]/mL), total testosterone 306 (250-1,100 ng/dL), SHBG 32 (10-50nmol/L), progesterone 7 (0.2-1.4 ng/mL), ACTH 345 (6-50 pg/mL), AM cortisol 4.4 (5-23 ug/dL), 17 hydroxyprogesterone 311 (32-307 ng/dL), androstenedione 1,926 (50-220 ng/dL), 11-deoxycortisol >10,000 (< or = 119 ng/dL). Cosyntropin stimulation test: 30-minute cortisol 11.1 (>18 ug/dL) and 60-minute cortisol 10.4 (>18 ug/dL). Based on clinical and lab findings a diagnosis of 11-beta hydroxylase deficiency was made. Spironolactone was started to counteract the excessive mineralocorticoid effects of deoxycorticosterone and hydrocortisone to decrease ACTH production. With this treatment, patient’s potassium and blood pressure gradually improved. IV antihypertensives were weaned as he transitioned to oral agents. This case demonstrates the importance of understanding and identifying the underlying pathophysiology of CAH to treat patients appropriately. This patient had a mineralocorticoid excess state, but adequate cortisol precursors to prevent adrenal crisis. He requires glucocorticoid therapy to prevent excessive ACTH from driving their BP and metabolic derangements. With appropriate diagnosis of 11-beta hydroxylase deficiency, patient’s excess risk of morbidity and mortality due to the downstream effects of uncontrolled CAH can be minimized. Presentation: 6/3/2024

7534 Characterizing The Presentation Of Non-Classical Congenital Adrenal Hyperplasia

Abstract Disclosure: S. Patel: None. M. Skamagas: None. A.C. Levine: None. M. Yau: None. Introduction: 21-hydroxylase deficiency, due to CYP21A2 gene mutations, is the most common steroidogenic enzymatic defect causing congenital adrenal hyperplasia (CAH). Disease severity is categorized into the classical and milder, non-classical (NCAH) form. Many patients go undiagnosed due to variable presentation and delayed onset. We aim to investigate the specific presenting concerns, age of onset, and genotypes associated with NCAH. Methods: A retrospective chart review of 285 patients with CAH seen over the past 2 years at our academic pediatric and adult endocrine clinics was performed. Records were reviewed for presenting concerns and age of symptom onset. CYP21A2 gene analysis was performed commercially via multiplex ligation-dependent probe amplification or next generation sequencing. Results: Of the 165 patients classified with NCAH, genotypes were available for 124 patients. Of the patients with a V281L allele, 43 were homozygous and 49 were heterozygous. 7 patients had the P30L allele and 7 had other allele combinations. The overall most common presenting concerns were early pubarche (29%), hirsutism (28%), and irregular menses (26%). In V281L homozygotes, family history most commonly led to diagnosis (30%). In patients with V281L heterozygosity or the P30L allele, the predominant concern was early pubarche (37% and 43% respectively). 15% of patients were screened prenatally or only due to family history and were asymptomatic at diagnosis. Patients’ age at diagnosis ranged from 0-40 years, with the mean age at diagnosis for the total group being 13.3 ± 8.9 years. Mean age of onset in symptomatic V281L homozygotes (15.4 ± 7.9 years) trended toward an older age compared to symptomatic V281L heterozygotes (15.1 ± 10.5 years) (P value = 0.90). Those who were heterozygous for V281L/P30L or undetermined whether homozygous for V281L or heterozygous with a deletion were excluded from age of onset comparisons. Discussion: The mean age of symptom onset was in adolescence and did not differ significantly between V281L homozygotes and heterozygotes. Early pubarche is a frequent presenting symptom in children with NCAH, and our data support this finding. P30L has been associated with a more severe phenotype than V281L, and in our cohort, the only patient presenting in adrenal crisis had a genotype with a P30L mutation. As NCAH is one of the most common autosomal recessive disorders in humans and there is an allelic predominance of V281L in NCAH patients, it is not surprising that a large percentage of V281L homozygotes were diagnosed due to family history prior to developing symptoms. Such patients need to be followed clinically and our data describing symptom onset could be useful in counseling these families and those with prenatal diagnoses. Presentation: 6/1/2024

7336 Decades In The Dark: The Long Road To Diagnosing And Treating Hypophosphatasia

Abstract Disclosure: V.A. Mendpara: None. G. Madrigal Loria: None. L.Z. Khan: None. Background: Hypophosphatasia (HPP) is a rare bone disorder that results from deficient activity of the tissue non-specific isoenzyme alkaline phosphatase (ALP).[1] This case highlights a patient whose diagnosis of this treatable genetic condition was significantly delayed for almost two decades, despite receiving care at a prominent academic institution. The patient's persistently low ALP levels in routine lab tests were overlooked by multiple clinicians, leading to a delay in her care and eventual treatment. Case presentation: A 61-year-old Caucasian woman presented at the endocrinology clinic with complaints of severe fatigue, generalized pain, multiple childhood fractures, and ongoing dental issues. The rheumatology clinic to which she was referred for polyarthralgia diagnosed her with Hypophosphatasia (HPP) after noting chronically low alkaline phosphatase (ALP) levels from her previous charts ranging from 15 to 24 U/L (normal range: 34 to 123 U/L) over two decades. Her serum calcium, parathyroid hormone (PTH), and 25-hydroxy vitamin D levels were within normal ranges. A DEXA scan revealed normal bone density, effectively ruling out osteoporosis. Further investigation showed elevated Vitamin B6 levels at 219.6 nmol/L (normal range: 20.0 to 125.0 nmol/L), raising suspicion for HPP. The patient's family history provided additional insight, with her mother having a history of short stature and fractures and her son experiencing premature tooth loss at the age of 2. A genetic evaluation identified a heterozygous pathogenic variant in the ALPL gene (c.881A>C, p.Asp294Ala), confirming the diagnosis of autosomal dominant HPP. Initiating treatment with Asfotase alfa, a medication targeting HPP, resulted in a marked improvement in the patient's symptoms. Discussion: This case shows the diagnostic complexities of HPP, stressing the significance of actively screening for this condition via ALP levels in routine laboratory testing or during osteoporosis evaluations. The diagnostic process is critical to distinguish HPP from primary osteoporosis, as treatment and potential risks differ significantly. Inadvertent use of bisphosphonates can worsen hypomineralization and lead to atypical femoral fractures in HPP patients. Asfotase alfa enzyme replacement therapy, available since 2015, offers a targeted approach by replacing the enzyme defect, thereby mitigating symptoms. Heightened awareness among healthcare providers of HPP in adults holds the potential to enhance diagnosis rates and facilitate improved treatment outcomes for this highly treatable condition.[1] Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, Eighth Edition. ASBMR. Presentation: 6/2/2024

Liver gene transfer for metabolite detoxification in inherited metabolic diseases.

Inherited metabolic disorders (IMDs) are a growing group of genetic diseases caused by defects in enzymes that mediate cellular metabolism, often resulting in the accumulation of toxic substrates. The liver is a highly metabolically active organ that hosts several thousands of chemical reactions. As such, it is an organ frequently affected in IMDs. In this article, we review current approaches for liver-directed gene-based therapy aimed at metabolite detoxification in a variety of IMDs. Moreover, we discuss current unresolved challenges in gene-based therapies for IMDs.

Engineering memory T cells as a platform for long-term enzyme replacement therapy in lysosomal storage disorders

Enzymopathy disorders are the result of missing or defective enzymes. Amongst these enzymopathies, mucopolysaccharidosis type I, is a rare genetic lysosomal storage disorder caused by mutations in the gene encoding alpha-L-iduronidase (IDUA), ultimately causes toxic build-up of glycosaminoglycans (GAGs). There is currently no cure and standard treatments provide insufficient relief to the skeletal structure and central nervous system (CNS). Human memory T cells (Tm) migrate throughout the body’s tissues and can persist for years, making them an attractive approach for cellular-based, systemic enzyme replacement therapy. Here, we tested genetically engineered, IDUA-expressing Tm as a cellular therapy in an immunodeficient mouse model of MPS I. Our results demonstrate that a single dose of engineered Tm leads to detectable IDUA enzyme levels in the blood for up to 22 weeks and reduced urinary GAG excretion. Furthermore, engineered Tm take up residence in nearly all tested tissues, producing IDUA and leading to metabolic correction of GAG levels in the heart, lung, liver, spleen, kidney, bone marrow, and the CNS, though only minimal improved cognition was observed. Our study indicates that genetically engineered Tm holds great promise as a platform for cellular-based enzyme replacement therapy for the treatment of mucopolysaccharidosis type I and potentially many other enzymopathies and protein deficiencies.

A Neonate Presenting with Severe Dehydration - A Case of Congenital Adrenal Hyperplasia with Salt Losing Crisis

Congenital adrenal hyperplasia (CAH) is a rare autosomal recessive disorder caused by mutations in genes involved in cortisol biosynthesis in the adrenal gland. Depending on the enzymatic defect, the symptoms, signs, and laboratory findings differ. The most common form, accounting for more than 95% of cases, is caused by 21-hydroxylase deficiency. Delay in the diagnosis and treatment can lead to life-threatening adrenal crisis with hemodynamic collapse. We report a case of a five-day-old male neonate with congenital adrenal hyperplasia and salt-wasting crisis. The diagnosis was made after comprehensive assessment of clinical features and laboratory investigations. He was treated with hydrocortisone and fludrocortisone and was discharged after one week.

Congenital Adrenal Hyperplasia: A Review of Current Knowledge and Future Directions

Introduction: Congenital adrenal hyperplasia (CAH) is a group of diseases in which genetic defects occur that disturb the synthesis of cortisol. The most common variant of CAH (95%-99%) is caused by 21-hydroxylase deficiency as a result of mutations in the CYP21A2 gene and is one of the most common monogenic diseases. CAH is characterized by androgen overproduction along with variable degrees of cortisol and aldosterone deficiency. Age at diagnosis can provide some information about the underlying mutations, with those diagnosed at birth/early infancy being at greater risk of developing serious enzyme defects. Classic and non-classical forms of this disorder have been described in the literature. CAH diagnosis is based on the clinical presentation, hormonal panel, Adrenocorticotropic Hormone (ACTH) stimulation test, and genetic testing. The main goals of treatment for congenital adrenal hyperplasia are glucocorticoid/mineralcorticoid supplementation, control of high adrenal androgen levels, fertility control, genetic counseling, and optimization of patients’ quality of life. Purpose of the work: This study aims to review and characterize the clinical and pathophysiological aspects of congenital adrenal hyperplasia. Materials and methods: A comprehensive analysis of research papers available on PubMed, Google Scholar, Web of Science, Embase and Scopus was undertaken using the searchterms encompassing the following keywords: congenital adrenal hyperplasia, 21-hydroxylase deficiency, CYP21A2 Results: Congenital adrenal hyperplasia is a heterogeneous group of genetic disorders that can lead to serious and even fatal complications in the form of adrenal crisis. Therefore, screening tests and early diagnosis are crucial and can save the lives of newborns. Treatment should be individualized and allow patients to achieve normal growth, sexual development, fertility and a better quality of life.

A Modular Biosensor Design for Quantitative Measurement of Free Nedd8.

The objective of our study was to develop a genetically encoded biosensor for quantification of Nedd8, a post-translational modifier that regulates cellular signals through conjugation to other proteins. Perturbations in the balance of free (i.e., unconjugated) and conjugated Nedd8 caused by defects in Nedd8 enzymes or cellular stress are implicated in various diseases. Despite the biological and biomedical importance of Nedd8 dynamics, no method exists for direct quantification of free Nedd8, hindering the study of Nedd8 and activities of its associated enzymes. Genetically encoded biosensors are established as tools to study other dynamic systems, but limitations of current biosensor design methods make them poorly suited for free Nedd8 quantification. We have developed a modular method to design genetically encoded biosensors that employs a target binding domain and two reporter domains positioned on opposite sides of the target binding site. Target quantification is based on competition between target binding and the interaction of the reporter domains. We applied our design strategy to free Nedd8 quantification by developing a selective binder for free Nedd8 and combining it with fluorescent or split nanoluciferase reporters. Our sensors produced quantifiable and specific signals for free Nedd8 and enabled real-time monitoring of deneddylation by DEN1 with a physiological substrate. Our sensor design will be useful for high-throughput screening for deneddylation inhibitors, which have potential in treatment of cancers such as acute lymphoblastic leukemia. The modular design strategy can be extended to develop genetically encoded quantitative biosensors for other proteins of interest.

Synthesis of a deuterated disaccharide internal standard for LC-MS/MS quantitation of heparan sulfate in biological samples

High levels of heparan sulfate (HS) are a marker for several mucopolysaccharidosis (MPS) disorders which are lysosomal storage diseases caused by genetic defects in HS-degrading enzymes. Quantitation of HS in biological samples is therefore critical for diagnosis and evaluating the efficacy of new therapies. Herein we present the efficient synthesis of a butylated GlcN-GlcA disaccharide and its deuterated derivative for use as an internal standard in a quantitative mass spectrometry-based assay for analysis of HS following butanolysis. The synthesis features the stereoselective 1,2-cis glycosylation of a GlcA acceptor with a 6-O-benzoyl-2-deoxy-2-azido thioglucoside donor.

Mitochondrial Dysfunction in Glycogen Storage Disorders (GSDs).

Glycogen storage disorders (GSDs) are a group of inherited metabolic disorders characterized by defects in enzymes involved in glycogen metabolism. Deficiencies in enzymes responsible for glycogen breakdown and synthesis can impair mitochondrial function. For instance, in GSD type II (Pompe disease), acid alpha-glucosidase deficiency leads to lysosomal glycogen accumulation, which secondarily impacts mitochondrial function through dysfunctional mitophagy, which disrupts mitochondrial quality control, generating oxidative stress. In GSD type III (Cori disease), the lack of the debranching enzyme causes glycogen accumulation and affects mitochondrial dynamics and biogenesis by disrupting the integrity of muscle fibers. Malfunctional glycogen metabolism can disrupt various cascades, thus causing mitochondrial and cell metabolic dysfunction through various mechanisms. These dysfunctions include altered mitochondrial morphology, impaired oxidative phosphorylation, increased production of reactive oxygen species (ROS), and defective mitophagy. The oxidative burden typical of GSDs compromises mitochondrial integrity and exacerbates the metabolic derangements observed in GSDs. The intertwining of mitochondrial dysfunction and GSDs underscores the complexity of these disorders and has significant clinical implications. GSD patients often present with multisystem manifestations, including hepatomegaly, hypoglycemia, and muscle weakness, which can be exacerbated by mitochondrial impairment. Moreover, mitochondrial dysfunction may contribute to the progression of GSD-related complications, such as cardiomyopathy and neurocognitive deficits. Targeting mitochondrial dysfunction thus represents a promising therapeutic avenue in GSDs. Potential strategies include antioxidants to mitigate oxidative stress, compounds that enhance mitochondrial biogenesis, and gene therapy to correct the underlying mitochondrial enzyme deficiencies. Mitochondrial dysfunction plays a critical role in the pathophysiology of GSDs. Recognizing and addressing this aspect can lead to more comprehensive and effective treatments, improving the quality of life of GSD patients. This review aims to elaborate on the intricate relationship between mitochondrial dysfunction and various types of GSDs. The review presents challenges and treatment options for several GSDs.

Pharmacogenomic Assessment of Genes Implicated in Thiopurine Metabolism and Toxicity in a UK Cohort of Pediatric Patients With Inflammatory Bowel Disease.

Thiopurine drugs are effective treatment options in inflammatory bowel disease and other conditions but discontinued in some patients due to toxicity. We investigated thiopurine-induced toxicity in a pediatric inflammatory bowel disease cohort by utilizing exome sequencing data across a panel of 46 genes, including TPMT and NUDT15. The cohort included 487 patients with a median age of 13.1 years. Of the 396 patients exposed to thiopurines, myelosuppression was observed in 11%, gastroenterological intolerance in 11%, hepatotoxicity in 4.5%, pancreatitis in 1.8%, and "other" adverse effects in 2.8%. TPMT (thiopurine S-methyltransferase) enzyme activity was normal in 87.4%, intermediate 12.3%, and deficient in 0.2%; 26% of patients with intermediate activity developed toxicity to thiopurines. Routinely genotyped TPMT alleles associated with defective enzyme activity were identified in 28 (7%) patients: TPMT*3A in 4.5%, *3B in 1%, and *3C in 1.5%. Of these, only 6 (21%) patients developed toxic responses. Three rare TPMT alleles (*3D, *39, and *40) not assessed on routine genotyping were identified in 3 patients, who all developed toxic responses. The missense variant p.R139C (NUDT15*3 allele) was identified in 4 patients (azathioprine 1.6mg/kg/d), but only 1 developed toxicity. One patient with an in-frame deletion variant p.G13del in NUDT15 developed myelosuppression at low doses. Per-gene deleteriousness score GenePy identified a significant association for toxicity in the AOX1 and DHFR genes. A significant association for toxicity was observed in the AOX1 and DHFR genes in individuals negative for the TPMT and NUDT15 variants. Patients harboring the NUDT15*3 allele, which is associated with myelosuppression, did not show an increased risk of toxicity.

Perioperative management in pediatric domino liver transplantation for metabolic disorders: A narrative review.

Domino liver transplantation and domino-auxiliary partial orthotopic liver transplantation are emerging techniques that can expand the liver donor pool and provide hope for children with liver disease. The innovative technique of domino liver transplantation has emerged as a pioneering strategy, capitalizing on structurally preserved livers from donors exhibiting single enzymatic defects within a morphologically normal context, effectively broadening the donor pool. Concurrently, the increasingly prevalent domino-auxiliary partial orthotopic liver transplantation method assumes a critical role in bolstering available donor resources. These advanced transplantation methods present a unique opportunity for pediatric patients who, despite having structurally and functionally intact livers and lacking early signs of portal hypertension or extrahepatic involvement, do not attain priority on conventional transplant lists. Utilizing optimal clinical conditions enhances posttransplant outcomes, benefiting patients who would otherwise endure extended waiting periods for traditional transplantation. The perioperative management of children undergoing these procedures is complex and requires careful consideration of some factors, including clinical and metabolic conditions of the specific metabolic disorder, and the need for tailored perioperative management planning. Furthermore, the prudent consideration of de novo disease development in the recipient assumes paramount significance when selecting suitable donors for domino liver transplantation, as it profoundly influences prognosis, mortality, and morbidity. This narrative review of domino liver transplantation will discuss the pathophysiology, clinical evaluation, perioperative management, and prognostic expectations, focusing on perioperative anesthetic considerations for children undergoing domino liver transplantation.

Current Clinical Guidelines for the Management of Patients with Glycogen Storage Disease

Glycogen storage disease refers to hereditary pathologies of carbohydrate metabolism, its cause is mutations of various genes encoding enzymes responsible for the synthesis and breakdown of glycogen. Due to enzyme defects, excessive glycogen deposition occurs in cells of various tissues, mainly in the liver and muscles. The authors present modern epidemiological data and features of the etiopathogenesis of glycogen storage disease, and give clinical characteristics of various types of this nosology. In accordance with the developed clinical guidelines, information is provided on laboratory, instrumental and morphological signs of glycogen storage disease in children, as well as on methods of treatment of glycogen storage disease. Due to the variety of clinical forms of glycogenosis, the article provides up-to-date information on three types of pathology that occur with predominant liver damage.

HOMOCYSTEINE AS A CARDIOVASCULAR RISK FACTOR

This article aims to review the evidence on the relationship between homocysteine and cardiovascular disease (CVD), as well as the possible mechanisms involved and therapeutic strategies to reduce homocysteine levels. Homocysteine is an amino acid that can accumulate in the blood for various reasons, such as enzymatic defects, nutritional deficiencies, or changes in liver or kidney function. Hyperhomocysteinemia is considered an independent risk factor for CVD as it affects the vascular endothelium, promotes LDL oxidation, and stimulates thrombosis. The article presents a meta-analysis of clinical and experimental studies that investigated the association between homocysteine and CVD, the mechanisms by which homocysteine can cause vascular damage, and ways to treat hyperhomocysteinemia, mainly through supplementation with B vitamins. The article concludes that homocysteine is both a marker and a causal factor of CVD, and that reducing its levels can prevent or slow the progression of the disease.

Evidence of Lysosomal β-Hexosaminidase Enzymatic Activity Associated with Extracellular Vesicles: Potential Applications for the Correction of Sandhoff Disease.

Extracellular vesicles (EVs) can be isolated from biological fluids and cell culture medium. Their nanometric dimension, relative stability, and biocompatibility have raised considerable interest for their therapeutic use as delivery vehicles of macromolecules, namely nucleic acids and proteins. Deficiency in lysosomal enzymes and associated proteins is at the basis of a group of genetic diseases known as lysosomal storage disorders (LSDs), characterized by the accumulation of undigested substrates into lysosomes. Among them, GM2 gangliosidoses are due to a deficiency in the activity of lysosomal enzyme β-hexosaminidase, leading to the accumulation of the GM2 ganglioside and severe neurological symptoms. Current therapeutic approaches, including enzyme replacement therapy (ERT), have proven unable to significantly treat these conditions. Here, we provide evidence that the lysosomal β-hexosaminidase enzyme is associated with EVs released by HEK cells and that the EV-associated activity can be increased by overexpressing the α-subunit of β-hexosaminidase. The delivery of EVs to β-hexosaminidase-deficient fibroblasts results in a partial cross-correction of the enzymatic defect. Overall findings indicate that EVs could be a source of β-hexosaminidase that is potentially exploitable for developing therapeutic approaches for currently untreatable LSDs.

A monoallelic UXS1 variant associated with short-limbed short stature.

Serine residues in the protein backbone of heavily glycosylated proteoglycans are bound to glycosaminoglycans through a tetrasaccharide linker. UXS1 encodes UDP-glucuronate decarboxylase 1, which catalyzes synthesis of UDP-xylose, the donor of the first building block in the linker. Defects in other enzymes involved in formation of the tetrasaccharide linker cause so-called linkeropathies, characterized by short stature, radio-ulnar synostosis, decreased bone density, congenital contractures, dislocations, and more. Whole exome sequencing was performed in a father and son who presented with a mild skeletal dysplasia, as well as the father's unaffected parents. Wild-type and mutant UXS1 were recombinantly expressed in Escherichia coli and purified. Enzyme activity was evaluated by LC-MS/MS. Invivo effects were studied using HeparinRed assay and metabolomics. The son had short long bones, normal epiphysis, and subtle metaphyseal changes especially in his legs. The likely pathogenic heterozygous variant NM_001253875.1(UXS1):c.557T>A p.(Ile186Asn) detected in the son was de novo in the father. Purified Ile186Asn-UXS1, in contrast to the wild-type, was not able to convert UDP-glucuronic acid to UDP-xylose. Plasma glycosaminoglycan levels were decreased in both son and father. This is the first report linking UXS1 to short-limbed short stature in humans.

L-serine deficiency: on the properties of the Asn133Ser variant of human phosphoserine phosphatase

The non-essential amino acid L-serine is involved in a number of metabolic pathways and in the brain its level is largely due to the biosynthesis from the glycolytic intermediate D-3-phosphoglycerate by the phosphorylated pathway (PP). This cytosolic pathway is made by three enzymes proposed to generate a reversible metabolon named the “serinosome”. Phosphoserine phosphatase (PSP) catalyses the last and irreversible step, representing the driving force pushing L-serine synthesis. Genetic defects of the PP enzymes result in strong neurological phenotypes. Recently, we identified the homozygous missense variant [NM_004577.4: c.398A > G p.(Asn133Ser)] in the PSPH, the PSP encoding gene, in two siblings with a neurodevelopmental syndrome and a myelopathy. The recombinant Asn133Ser enzyme does not show significant alterations in protein conformation and dimeric oligomerization state, as well as in enzymatic activity and functionality of the reconstructed PP. However, the Asn133Ser variant is less stable than wild-type PSP, a feature also apparent at cellular level. Studies on patients’ fibroblasts also highlight a strong decrease in the level of the enzymes of the PP, a partial nuclear and perinuclear localization of variant PSP and a stronger perinuclear aggregates formation. We propose that these alterations contribute to the formation of a dysfunctional serinosome and thus to the observed reduction of L-serine, glycine and D-serine levels (the latter playing a crucial role in modulating NMDA receptors). The characterization of patients harbouring the Asn133Ser PSP substitution allows to go deep into the molecular mechanisms related to L-serine deficit and to suggest treatments to cope with the observed amino acids alterations.