The Immunogenomic Landscape of Peripheral High-Dose IL-2 Pharmacodynamics in Patients with Metastatic Renal Cell Carcinoma: A Benchmark for Next-Generation IL-2-Based Immunotherapies.

High-dose (HD) IL-2 was the first immuno-oncology agent approved for treating advanced renal cell carcinoma and metastatic melanoma, but its use was limited because of substantial toxicities. Multiple next-generation IL-2 agents are being developed to improve tolerability. However, a knowledge gap still exists for the genomic markers that define the target pharmacology for HD IL-2 itself. In this retrospective observational study, we collected PBMC samples from 23 patients with metastatic renal cell carcinoma who were treated with HD IL-2 between 2009 and 2015. We previously reported the results of flow cytometry analyses. In this study, we report the results of our RNA-sequencing immunogenomic survey, which was performed on bulk PBMC samples from immediately before (day 1), during (day 3), and after treatment (day 5) in cycle 1 and/or cycle 2 of the first course of HD IL-2. As part of a detailed analysis of immunogenomic response to HD IL-2 treatment, we analyzed the changes in individual genes and immune gene signatures. By day 3, most lymphoid cell types had transiently decreased, whereas myeloid transcripts increased. Although most genes and/or signatures generally returned to pretreatment expression levels by day 5, certain ones representative of B cell, NK cell, and T cell proliferation and effector functions continued to increase, along with B cell (but not T cell) oligoclonal expansion. Regulatory T cells progressively expanded during and after treatment. They showed strong negative correlation with myeloid effector cells. This detailed RNA-sequencing immunogenomic survey of IL-2 pharmacology complements results of prior flow cytometry analyses. These data provide valuable pharmacological context for assessing PBMC gene expression data from patients dosed with IL-2-related compounds that are currently in development.

BCKDK deficiency: a treatable neurodevelopmental disease amenable to newborn screening.

There are few causes of treatable neurodevelopmental diseases described to date. Branched-chain ketoacid dehydrogenase kinase (BCKDK) deficiency causes branched-chain amino acid (BCAA) depletion and is linked to a neurodevelopmental disorder characterized by autism, intellectual disability and microcephaly. We report the largest cohort of patients studied, broadening the phenotypic and genotypic spectrum. Moreover, this is the first study to present newborn screening findings and mid-term clinical outcome. In this cross-sectional study, patients with a diagnosis of BCKDK deficiency were recruited via investigators' practices through a MetabERN initiative. Clinical, biochemical and genetic data were collected. Dried blood spot (DBS) newborn screening (NBS) amino acid profiles were retrieved from collaborating centres and compared to a healthy newborn reference population. Twenty-one patients with BCKDK mutations were included from 13 families. Patients were diagnosed between 8 months and 16 years (mean: 5.8 years, 43% female). At diagnosis, BCAA levels (leucine, valine and isoleucine) were below reference values in plasma and in CSF. All patients had global neurodevelopmental delay; 18/21 had gross motor function (GMF) impairment with GMF III or worse in 5/18, 16/16 intellectual disability, 17/17 language impairment, 12/17 autism spectrum disorder, 9/21 epilepsy, 12/15 clumsiness, 3/21 had sensorineural hearing loss and 4/20 feeding difficulties. No microcephaly was observed at birth, but 17/20 developed microcephaly during follow-up. Regression was reported in six patients. Movement disorder was observed in 3/21 patients: hyperkinetic movements (1), truncal ataxia (1) and dystonia (2). After treatment with a high-protein diet (≥ 2 g/kg/day) and BCAA supplementation (100-250 mg/kg/day), plasma BCAA increased significantly (P < 0.001), motor functions and head circumference stabilized/improved in 13/13 and in 11/15 patients, respectively. Among cases with follow-up data, none of the three patients starting treatment before 2 years of age developed autism at follow-up. The patient with the earliest age of treatment initiation (8 months) showed normal development at 3 years of age. NBS in DBS identified BCAA levels significantly lower than those of the normal population. This work highlights the potential benefits of dietetic treatment, in particular early introduction of BCAA. Therefore, it is of utmost importance to increase awareness about this treatable disease and consider it as a candidate for early detection by NBS programmes.

Bi-allelic Variants in TKFC Encoding Triokinase/FMN Cyclase Are Associated with Cataracts and Multisystem Disease.

We report an inborn error of metabolism caused by TKFC deficiency in two unrelated families. Rapid trio genome sequencing in family 1 and exome sequencing in family 2 excluded known genetic etiologies, and further variant analysis identified rare homozygous variants in TKFC. TKFC encodes a bifunctional enzyme involved in fructose metabolism through its glyceraldehyde kinase activity and in the generation of riboflavin cyclic 4',5'-phosphate (cyclic FMN) through an FMN lyase domain. The TKFC homozygous variants reported here are located within the FMN lyase domain. Functional assays in yeast support the deleterious effect of these variants on protein function. Shared phenotypes between affected individuals with TKFC deficiency include cataracts and developmental delay, associated with cerebellar hypoplasia in one case. Further complications observed in two affected individuals included liver dysfunction and microcytic anemia, while one had fatal cardiomyopathy with lactic acidosis following a febrile illness. We postulate that deficiency of TKFC causes disruption of endogenous fructose metabolism leading to generation of by-products that can cause cataract. In line with this, an affected individual had mildly elevated urinary galactitol, which has been linked to cataract development in the galactosemias. Further, in light of a previously reported role of TKFC in regulating innate antiviral immunity through suppression of MDA5, we speculate that deficiency of TKFC leads to impaired innate immunity in response to viral illness, which may explain the fatal illness observed in the most severely affected individual.

Safety and efficacy of avalglucosidase alfa in individuals with infantile-onset Pompe disease enrolled in the phase 2, open-label Mini-COMET study: The 6-month primary analysis report.

PURPOSE: Mini-COMET (NCT03019406; Sanofi) is a phase 2, open-label, ascending-dose, 3-cohort study, evaluating avalglucosidase alfa safety, pharmacokinetics, and efficacy in individuals with infantile-onset Pompe disease aged <18 years who previously received alglucosidase alfa and showed clinical decline (cohorts 1 and 2) or suboptimal response (cohort 3). METHODS: During a 25-week primary analysis period, cohorts 1 and 2 received avalglucosidase alfa 20 and 40 mg/kg every other week, respectively, for 6 months, whereas cohort 3 individuals were randomized (1:1) to receive avalglucosidase alfa 40 mg/kg every other week or alglucosidase alfa (current stable dose) for 6 months. RESULTS: In total, 22 individuals were enrolled (cohort 1 [n = 6], cohort 2 [n = 5], cohort 3-avalglucosidase alfa [n = 5], and cohort 3-alglucosidase alfa [n = 6]). Median treatment compliance was 100%. None of the individuals discontinued treatment or died. Percentages of individuals with treatment-emergent adverse events were similar across dose and treatment groups. No serious or severe treatment-related treatment-emergent adverse events occurred. Trends for better motor function from baseline to week 25 were observed for 40 mg/kg every other week avalglucosidase alfa compared with either 20 mg/kg every other week avalglucosidase alfa or alglucosidase alfa up to 40 mg/kg weekly. CONCLUSION: These data support the positive clinical effect of avalglucosidase alfa in patients with infantile-onset Pompe disease previously declining on alglucosidase alfa.

The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria.

Argininosuccinate lyase (ASL) is integral to the urea cycle detoxifying neurotoxic ammonia and the nitric oxide (NO) biosynthesis cycle. Inherited ASL deficiency causes argininosuccinic aciduria (ASA), a rare disease with hyperammonemia and NO deficiency. Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis. A neurodegenerative phenotype has been proposed in ASA. To better characterise this neurodegenerative phenotype in ASA, we conducted a retrospective study in six paediatric and adult metabolic centres in the UK in 2022. We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour. We analysed neuroimaging with diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) in an individual with ASA with movement disorders. We assessed conventional and DTI MRI alongside single photon emission computer tomography (SPECT) with dopamine analogue radionuclide 123 I-ioflupane, in Asl-deficient mice treated by hASL mRNA with normalised ureagenesis. Movement disorders in ASA appear in the second and third decades of life, becoming more prevalent with ageing and independent from the age of onset of hyperammonemia. Neuroimaging can show abnormal DTI features affecting both grey and white matter, preferentially basal ganglia. ASA mouse model with normalised ureagenesis did not recapitulate these DTI findings and showed normal 123 I-ioflupane SPECT and cerebral dopamine metabolomics. Altogether these findings support the pathophysiology of a late-onset movement disorder with cell-autonomous functional central catecholamine dysregulation but without or limited neurodegeneration of dopaminergic neurons, making these symptoms amenable to targeted therapy.

Prenatal diagnosis of mucopolysaccharidosis type VII facilitating treatment in neonatal period.

Duo exome testing was performed on a fetus conceived via in vitro fertilization with an egg donor. The fetus presented with non-immune hydrops fetalis (NIHF) at 20 + 0 weeks gestation. Two variants were detected in the GUSB gene. Biallelic pathogenic variants cause mucopolysaccharidosis type VII (MPS-VII), which can present with NIHF prenatally. At the time of analysis and initial report, one variant was classified as likely pathogenic and the other as of uncertain clinical significance. Biochemical testing of the amniotic fluid supernatant showed elevated glycosaminoglycans and low ß-glucuronidase activity consistent with the diagnosis of MPS-VII. This evidence allowed the upgrade of the pathogenicity for both variants, confirming the diagnosis of MPS-VII. The infant was born at 36 + 5 weeks and enzyme replacement therapy (ERT) using vestronidase was initiated at 20 days with planning for hematopoietic stem cell transplant ongoing. The ERT therapy has been well tolerated, with decreasing quantitative urine glycosaminoglycans. Long-term follow up is required to determine whether treatment has been successful. This case demonstrates the utility of alternative testing methods to clarify the pathogenicity of variants and the clinical utility of obtaining a diagnosis antenatally in facilitating treatment in the neonatal period, and specifically highlights MPS-VII as a treatable cause of NIHF.

Tuberous xanthoma secondary to homozygous familial hypercholesterolaemia: a life-threatening diagnosis.

We report the case of a 9-year-old girl who presented with asymptomatic lesions on the extensor surfaces of the elbows and knees, in keeping with tuberous xanthoma. She was investigated and diagnosed with homozygous familial hypercholesterolaemia, and commenced on lipid-lowering treatment. We highlight the importance of identification of this condition early, such that life-saving treatment can be initiated and premature death avoided. Click here for the corresponding questions to this CME article.

Novel therapies for mucopolysaccharidosis type III.

Mucopolysaccharidosis type III (MPS III) or Sanfilippo disease is an orphan inherited lysosomal storage disease and one of the most common MPS subtypes. The classical presentation is an infantile-onset neurodegenerative disease characterised by intellectual regression, behavioural and sleep disturbances, loss of ambulation, and early death. Unlike other MPS, no disease-modifying therapy has yet been approved. Here, we review the numerous approaches of curative therapy developed for MPS III from historical ineffective haematopoietic stem cell transplantation and substrate reduction therapy to the promising ongoing clinical trials based on enzyme replacement therapy or adeno-associated or lentiviral vectors mediated gene therapy. Preclinical studies are presented alongside the most recent translational first-in-man trials. In addition, we present experimental research with preclinical mRNA and gene editing strategies. Lessons from animal studies and clinical trials have highlighted the importance of an early therapy before extensive neuronal loss. A disease-modifying therapy for MPS III will undoubtedly mandate development of new strategies for early diagnosis.

Microbiota regulate intestinal epithelial gene expression by suppressing the transcription factor Hepatocyte nuclear factor 4 alpha.

Microbiota influence diverse aspects of intestinal physiology and disease in part by controlling tissue-specific transcription of host genes. However, host genomic mechanisms mediating microbial control of intestinal gene expression are poorly understood. Hepatocyte nuclear factor 4 (HNF4) is the most ancient family of nuclear receptor transcription factors with important roles in human metabolic and inflammatory bowel diseases, but a role in host response to microbes is unknown. Using an unbiased screening strategy, we found that zebrafish Hnf4a specifically binds and activates a microbiota-suppressed intestinal epithelial transcriptional enhancer. Genetic analysis revealed that zebrafish hnf4a activates nearly half of the genes that are suppressed by microbiota, suggesting microbiota negatively regulate Hnf4a. In support, analysis of genomic architecture in mouse intestinal epithelial cells disclosed that microbiota colonization leads to activation or inactivation of hundreds of enhancers along with drastic genome-wide reduction of HNF4A and HNF4G occupancy. Interspecies meta-analysis suggested interactions between HNF4A and microbiota promote gene expression patterns associated with human inflammatory bowel diseases. These results indicate a critical and conserved role for HNF4A in maintaining intestinal homeostasis in response to microbiota.

Free urinary glycosylated hydroxylysine as an indicator of altered collagen degradation in the mucopolysaccharidoses.

Extracellular matrix (ECM) disruption is known to be an early pathological feature of the Mucopolysaccharidoses (MPS). Collagen is the main component of the ECM and its metabolism could act as a useful indicator of ECM disruption. We have measured the specific collagen breakdown products; urinary free hydroxylated (Lys-OH) and glycosylated hydroxylysines (Lys-O-Gal and Lys-O-GalGlc) in MPS patients using a tandem liquid chromatography tandem mass spectrometry assay. A pilot study cohort analysis indicated that concentrations of lysine and Lys-OH were raised significantly in MPS I (Hurler) disease patients. Lys-O-GalGlc was raised in MPS II and MPS VI patients and demonstrated a significant difference between MPS I Hurler and an MPS I Hurler-Scheie group. Further analysis determined an age association for glycosylated hydroxylysine in control samples similar to that observed for the glycosaminoglycans. Using defined age ranges and treatment naïve patient samples we confirmed an increase in glycosylated hydroxylysines in MPS I and in adult MPS IVA. We also looked at the ratio of Lys-O-Gal to Lys-O-GalGlc, an indicator of the source of collagen degradation, and noticed a significant change in the ratio for all pediatric MPS I, II, and IV patients, and a small significant increase in adult MPS IV. This indicated that the collagen degradation products were coming from a source other than bone such as cartilage or connective tissue. To see how specific the changes in glycosylated hydroxylysine were to MPS patients we also looked at levels in patients with other inherited metabolic disorders. MPS patients showed a trend towards increased glycosylated hydroxylysines and an elevated ratio compared to other metabolic disorders that included Battens disease, Fabry disease, Pyridoxine-dependent epilepsy (due to mutations in ALDH7A1), and Niemann Pick C disease.

Commensal Bacteria Regulate Gene Expression and Differentiation in Vertebrate Olfactory Systems Through Transcription Factor REST.

Sensory systems such as the olfactory system detect chemical stimuli and thereby determine the relationships between the animal and its surroundings. Olfaction is one of the most conserved and ancient sensory systems in vertebrates. The vertebrate olfactory epithelium is colonized by complex microbial communities, but microbial contribution to host olfactory gene expression remains unknown. In this study, we show that colonization of germ-free zebrafish and mice with microbiota leads to widespread transcriptional responses in olfactory organs as measured in bulk tissue transcriptomics and RT-qPCR. Germ-free zebrafish olfactory epithelium showed defects in pseudostratification; however, the size of the olfactory pit and the length of the cilia were not different from that of colonized zebrafish. One of the mechanisms by which microbiota control host transcriptional programs is by differential expression and activity of specific transcription factors (TFs). REST (RE1 silencing transcription factor, also called NRSF) is a zinc finger TF that binds to the conserved motif repressor element 1 found in the promoter regions of many neuronal genes with functions in neuronal development and differentiation. Colonized zebrafish and mice showed increased nasal expression of REST, and genes with reduced expression in colonized animals were strongly enriched in REST-binding motifs. Nasal commensal bacteria promoted in vitro differentiation of Odora cells by regulating the kinetics of REST expression. REST knockdown resulted in decreased Odora cell differentiation in vitro. Our results identify a conserved mechanism by which microbiota regulate vertebrate olfactory transcriptional programs and reveal a new role for REST in sensory organs.

Isolated aortic root dilation in homocystinuria.

BACKGROUND: Vascular complications in homocystinuria have been known for many years, but there have been no reports to date on involvement of the ascending aorta. METHODS: We conducted a cross-sectional study of patients with homocystinuria, known to a single metabolic centre, and evaluated in 2016 with a transthoracic echocardiogram. Aortic root dilation was defined as Z-score ≥ 2.0 SD, and graded mild (Z-score 2.0-3.0), moderate (Z-score 3.01-4.0) and severe (Z-score > 4.0). RESULTS: The study population included 34 patients, median age of 44.3 years (IQR 33.3-52.2), 50% males, 69% diagnosed aged <18 years and 29% pyridoxine-responsive. Eight (24%) had a history of hypertension. Seven patients (21%) were found to have a dilation of the aortic root, mild in two cases (6%), moderate in four (12%) and severe in one (3%). None had dilation of the ascending aorta. Significant aortic regurgitation, secondary to moderate aortic root dilation, was documented in two patients. A single patient had significant mitral regurgitation due to prolapse of both valve leaflets, as well as mild aortic root dilation. Comparing patients with a dilation of the aortic root to those without, there were no significant clinical, laboratory or echocardiographic differences, with the only exception being that the diameter of the ascending aorta was larger in the group with a dilated aortic root, albeit within normal limits. CONCLUSIONS: A subset of patients with homocystinuria have isolated dilation of the aortic root similar to that observed in Marfan syndrome.

Thalamic and dentate nucleus abnormalities in the brain of children with Gaucher disease.

Gaucher disease (GD) represents the most common lysosomal storage defect. It is classified into three phenotypes: type 1 non-neuronopathic, type 2 acute neuronopathic, and type 3 subacute/chronic neuronopathic. Although children affected by GD may present with a broad spectrum of neurological signs, brain magnetic resonance imaging (MRI) findings are usually normal or non-specific. We report three cases of GD with previously undescribed brain MRI changes mainly affecting the thalami and/or the dentate nuclei. We discuss the possible etiopathogenesis of these abnormalities. Correlation between brain MRI abnormalities, neurological symptoms, and treatment efficacy is still unclear.

Expanding the phenotype in argininosuccinic aciduria: need for new therapies.

OBJECTIVES: This UK-wide study defines the natural history of argininosuccinic aciduria and compares long-term neurological outcomes in patients presenting clinically or treated prospectively from birth with ammonia-lowering drugs. METHODS: Retrospective analysis of medical records prior to March 2013, then prospective analysis until December 2015. Blinded review of brain MRIs. ASL genotyping. RESULTS: Fifty-six patients were defined as early-onset (n = 23) if symptomatic < 28 days of age, late-onset (n = 23) if symptomatic later, or selectively screened perinatally due to a familial proband (n = 10). The median follow-up was 12.4 years (range 0-53). Long-term outcomes in all groups showed a similar neurological phenotype including developmental delay (48/52), epilepsy (24/52), ataxia (9/52), myopathy-like symptoms (6/52) and abnormal neuroimaging (12/21). Neuroimaging findings included parenchymal infarcts (4/21), focal white matter hyperintensity (4/21), cortical or cerebral atrophy (4/21), nodular heterotopia (2/21) and reduced creatine levels in white matter (4/4). 4/21 adult patients went to mainstream school without the need of additional educational support and 1/21 lives independently. Early-onset patients had more severe involvement of visceral organs including liver, kidney and gut. All early-onset and half of late-onset patients presented with hyperammonaemia. Screened patients had normal ammonia at birth and received treatment preventing severe hyperammonaemia. ASL was sequenced (n = 19) and 20 mutations were found. Plasma argininosuccinate was higher in early-onset compared to late-onset patients. CONCLUSIONS: Our study further defines the natural history of argininosuccinic aciduria and genotype-phenotype correlations. The neurological phenotype does not correlate with the severity of hyperammonaemia and plasma argininosuccinic acid levels. The disturbance in nitric oxide synthesis may be a contributor to the neurological disease. Clinical trials providing nitric oxide to the brain merit consideration.

How to use white blood cell enzyme assays.

White blood cell (leucocyte) enzyme assays are an important part of the investigation of potential metabolic disorders, in particular, lysosomal storage disorders. It is imperative that appropriate tests are selected, and that knowledge of the limitations of these assays is applied to avoid erroneous conclusions about confirmation or exclusion of diagnoses.

Transient neonatal liver disease after maternal antenatal intravenous Ig infusions in gestational alloimmune liver disease associated with neonatal haemochromatosis.

OBJECTIVES: Neonatal haemochromatosis is a rare gestational disease that results in severe foetal liver disease with extrahepatic iron overload, sparing the reticuloendothelial system. Recurrence can be prevented with intravenous immunoglobulin (IVIG) infusions during pregnancy, supporting an alloimmune aetiology. The aim of the study was to assess the effect of antenatal treatment with IVIG infusion on the outcome of pregnancies in women with a history of documented neonatal haemochromatosis likely owing to gestational alloimmune disease and to analyse IVIG tolerance. METHODS: From 2004 to 2012, 8 pregnant women were treated with IVIG at 1 g/kg body weight weekly from 18 weeks' gestation until birth in a prospective multicentre study. RESULTS: All 8 neonates born to the treated women survived. Five developed mild neonatal liver disease with hepatomegaly (n = 1), hyperechogenic liver (n = 2), abnormal liver function tests (n = 1), raised serum ferritin (n = 3) and α-fetoprotein (n = 5) levels, or mild iron overload on liver magnetic resonance imaging (n = 1). Ferritin and α-fetoprotein levels normalised before 14 days and 2 months, respectively. A per-mother-basis analysis comparing outcomes of treated (n = 8) and untreated (n = 9) gestations showed a significant improvement in the survival of neonates with gestational IVIG therapy (survival 8/8 vs 0/9, P < 0.001). Adverse effects of IVIG infusion occurred in 5 mothers leading to discontinuation of treatment in 1 case. Preterm neonates born before 37 weeks' gestation had a decreased risk of neonatal liver disease (P = 0.04). CONCLUSIONS: Antenatal treatment with IVIG infusion in women at risk for gestational alloimmune disease recurrence improves the outcome of pregnancies despite mild signs of transient neonatal liver disease.

Real-World Experience of Carglumic Acid for Methylmalonic and Propionic Acidurias: An Interim Analysis of the Multicentre Observational PROTECT Study.

BACKGROUND AND OBJECTIVE: Methylmalonic aciduria (MMA) and propionic aciduria (PA) are organic acidurias characterised by the accumulation of toxic metabolites and hyperammonaemia related to secondary N-acetylglutamate deficiency. Carglumic acid, a synthetic analogue of N-acetylglutamate, decreases ammonia levels by restoring the functioning of the urea cycle. However, there are limited data available on the long-term safety and effectiveness of carglumic acid. Here, we present an interim analysis of the ongoing, long-term, prospective, observational PROTECT study (NCT04176523), which is investigating the long-term use of carglumic acid in children and adults with MMA and PA. METHODS: Individuals with MMA or PA from France, Germany, Italy, Norway, Spain, Sweden and the UK who have received at least 1 year of carglumic acid treatment as part of their usual care are eligible for inclusion. The primary objective is the number and duration of acute metabolic decompensation events with hyperammonaemia (ammonia level >159 µmol/L during a patient's first month of life or >60 µmol/L thereafter, with an increased lactate level [> 1.8 mmol/L] and/or acidosis [pH < 7.35]) before and after treatment with carglumic acid. Peak plasma ammonia levels during the last decompensation event before and the first decompensation event after carglumic acid initiation, and the annualised rate of decompensation events before and after treatment initiation are also being assessed. Secondary objectives include the duration of hospital stay associated with decompensation events. Data are being collected at approximately 12 months' and 18 months' follow-up. RESULTS: Of the patients currently enrolled in the PROTECT study, data from ten available patients with MMA (n = 4) and PA (n = 6) were analysed. The patients had received carglumic acid for 14-77 (mean 36) months. Carglumic acid reduced the median peak ammonia level of the total patient population from 250 µmol/L (range 97-2569) before treatment to 103 µmol/L (range 97-171) after treatment. The annualised rate of acute metabolic decompensations with hyperammonaemia was reduced by a median of - 41% (range - 100% to + 60%) after treatment with carglumic acid. Of the five patients who experienced a decompensation event before treatment and for whom a post-treatment rate could be calculated, the annualised decompensation event rate was lower after carglumic acid treatment in four patients. The mean duration of hospital inpatient stay during decompensation events was shorter after than before carglumic acid treatment initiation in four of five patients for whom length of stay could be calculated. CONCLUSIONS: In this group of patients with MMA and PA, treatment with carglumic acid for at least 1 year reduced peak plasma ammonia levels in the total patient population and reduced the frequency of metabolic decompensation events, as well as the duration of inpatient stay due to metabolic decompensations in a subset of patients. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, NCT04176523. Registered 25 November, 2019, retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04176523 .

Wilms tumor gene on X chromosome (WTX) inhibits degradation of NRF2 protein through competitive binding to KEAP1 protein.

WTX is a tumor suppressor protein that is lost or mutated in up to 30% of cases of Wilms tumor. Among its known functions, WTX interacts with the ß-transducin repeat containing family of ubiquitin ligase adaptors and promotes the ubiquitination and degradation of the transcription factor ß-catenin, a key control point in the WNT/ß-catenin signaling pathway. Here, we report that WTX interacts with a second ubiquitin ligase adaptor, KEAP1, which functions to regulate the ubiquitination of the transcription factor NRF2, a key control point in the antioxidant response. Surprisingly, we find that unlike its ability to promote the ubiquitination of ß-catenin, WTX inhibits the ubiquitination of NRF2. WTX and NRF2 compete for binding to KEAP1, and thus loss of WTX leads to rapid ubiquitination and degradation of NRF2 and a reduced response to cytotoxic insult. These results expand our understanding of the molecular mechanisms of WTX and reveal a novel regulatory mechanism governing the antioxidant response.

Recessive germline SDHA and SDHB mutations causing leukodystrophy and isolated mitochondrial complex II deficiency.

BACKGROUND: Isolated complex II deficiency is a rare form of mitochondrial disease, accounting for approximately 2% of all respiratory chain deficiency diagnoses. The succinate dehydrogenase (SDH) genes (SDHA, SDHB, SDHC and SDHD) are autosomally-encoded and transcribe the conjugated heterotetramers of complex II via the action of two known assembly factors (SDHAF1 and SDHAF2). Only a handful of reports describe inherited SDH gene defects as a cause of paediatric mitochondrial disease, involving either SDHA (Leigh syndrome, cardiomyopathy) or SDHAF1 (infantile leukoencephalopathy). However, all four SDH genes, together with SDHAF2, have known tumour suppressor functions, with numerous germline and somatic mutations reported in association with hereditary cancer syndromes, including paraganglioma and pheochromocytoma. METHODS AND RESULTS: Here, we report the clinical and molecular investigations of two patients with histochemical and biochemical evidence of a severe, isolated complex II deficiency due to novel SDH gene mutations; the first patient presented with cardiomyopathy and leukodystrophy due to compound heterozygous p.Thr508Ile and p.Ser509Leu SDHA mutations, while the second patient presented with hypotonia and leukodystrophy with elevated brain succinate demonstrated by MR spectroscopy due to a novel, homozygous p.Asp48Val SDHB mutation. Western blotting and BN-PAGE studies confirmed decreased steady-state levels of the relevant SDH subunits and impairment of complex II assembly. Evidence from yeast complementation studies provided additional support for pathogenicity of the SDHB mutation. CONCLUSIONS: Our report represents the first example of SDHB mutation as a cause of inherited mitochondrial respiratory chain disease and extends the SDHA mutation spectrum in patients with isolated complex II deficiency.