Generation of induced pluripotent stem cells (UCLi024-A) from a patient with argininosuccinate lyase deficiency carrying a homozygous c.437G > A (p.Arg146Gln) mutation

Argininosuccinic aciduria (ASA) is a rare inherited metabolic disease caused by argininosuccinate lyase (ASL) deficiency. Patients with ASA present with hyperammonaemia due to an impaired urea cycle pathway in the liver, and systemic disease with epileptic encephalopathy, chronic liver disease, and arterial hypertension. A human induced pluripotent stem cell (iPSC) line from the fibroblasts of a patient with ASA with homozygous pathogenic c.437G > A mutation of hASL was generated. Characterization of the cell line demonstrated pluripotency, differentiation potential and normal karyotype. This cell line, called UCLi024-A, can be utilized for in vitro disease modelling of ASA, and design of novel therapeutics.

First in man study of intravitreal tripeptidyl peptidase 1 for CLN2 retinopathy

BACKGROUND/OBJECTIVES

CLN2 Batten Disease is a fatal neurodegenerative condition of childhood associated with retinal dystrophy and blindness. Intracerebroventricular infusion of rhTPP1 greatly slows the rate of neurodegenerative decline but not retinopathy. Intravitreal rhTPP1 is known to slow retinal degeneration in a canine model of CLN2. We report a first-in-man controlled clinical trial of intravitreal rhTPP1 for CLN2 associated retinal dystrophy.

SUBJECTS/METHODS

8 children aged 5-9 with CLN2 Batten Disease were prospectively enroled. Severely affected patients were preferentially selected, provided that vision was better than no perception of light. Children underwent 8 weekly intravitreal injections of rhTPP1 (0.2 mg in 0.05 ml) into the right eye for 12-18 months. The left eye was untreated and acts as a paired control. The primary outcome was safety based on the clinical detection of complications. A secondary outcome was paracentral macular volume (PMV) measured by spectral domain OCT. Linear regression/paired t tests were used to compare rates of decline.

RESULTS

No severe adverse reactions (uveitis, raised IOP, media opacity) occurred. The mean baseline PMV was 1.28 mm3(right), 1.27 mm3(left). 3 of the youngest patients exhibited bilateral progressive retinal thinning (p < 0.05), whereas retinal volume was stable in the remaining 5 patients. In the 3 patients undergoing retinal degeneration, the rate of PMV loss was slower in the treated vs. untreated eye (p = 0.000042, p = 0.0011, p = 0.00022).

CONCLUSIONS

Intravitreal rhTPP1 appears to be a safe and effective treatment for CLN2 related retinopathy however commencement of treatment early in the course of disease is more likely to be efficacious.

Trial of N-Acetyl-l-Leucine in Niemann-Pick Disease Type C

BACKGROUND

Niemann-Pick disease type C is a rare lysosomal storage disorder. We evaluated the safety and efficacy of N-acetyl-l-leucine (NALL), an agent that potentially ameliorates lysosomal and metabolic dysfunction, for the treatment of Niemann-Pick disease type C.

METHODS

In this double-blind, placebo-controlled, crossover trial, we randomly assigned patients 4 years of age or older with genetically confirmed Niemann-Pick disease type C in a 1:1 ratio to receive NALL for 12 weeks, followed by placebo for 12 weeks, or to receive placebo for 12 weeks, followed by NALL for 12 weeks. NALL or matching placebo was administered orally two to three times per day, with patients 4 to 12 years of age receiving weight-based doses (2 to 4 g per day) and those 13 years of age or older receiving a dose of 4 g per day. The primary end point was the total score on the Scale for the Assessment and Rating of Ataxia (SARA; range, 0 to 40, with lower scores indicating better neurologic status). Secondary end points included scores on the Clinical Global Impression of Improvement, the Spinocerebellar Ataxia Functional Index, and the Modified Disability Rating Scale. Crossover data from the two 12-week periods in each group were included in the comparisons of NALL with placebo.

RESULTS

A total of 60 patients 5 to 67 years of age were enrolled. The mean baseline SARA total scores used in the primary analysis were 15.88 before receipt of the first dose of NALL (60 patients) and 15.68 before receipt of the first dose of placebo (59 patients; 1 patient never received placebo). The mean (±SD) change from baseline in the SARA total score was -1.97±2.43 points after 12 weeks of receiving NALL and -0.60±2.39 points after 12 weeks of receiving placebo (least-squares mean difference, -1.28 points; 95% confidence interval, -1.91 to -0.65; P<0.001). The results for the secondary end points were generally supportive of the findings in the primary analysis, but these were not adjusted for multiple comparisons. The incidence of adverse events was similar with NALL and placebo, and no treatment-related serious adverse events occurred.

CONCLUSIONS

Among patients with Niemann-Pick disease type C, treatment with NALL for 12 weeks led to better neurologic status than placebo. A longer period is needed to determine the long-term effects of this agent in patients with Niemann-Pick disease type C. (Funded by IntraBio; ClinicalTrials.gov number, NCT05163288; EudraCT number, 2021-005356-10.).

Characterization of two human induced pluripotent stem cell lines derived from Batten disease patient fibroblasts harbouring CLN5 mutations

The neuronal ceroid lipofuscinoses (NCLs) are a group of common inherited neurodegenerative disorders of childhood. All forms of NCLs are life-limiting with no curative treatments. Most of the 13 NCL genes encode proteins residing in endolysosomal pathways, such as CLN5, a potential lysosomal enzyme. Two induced pluripotent stem cell lines (hiPSCs) were generated from skin fibroblasts of CLN5 disease patients via non-integrating Sendai virus reprogramming. They demonstrate typical stem cell morphology, express pluripotency markers, exhibit trilineage differentiation potential and also successfully differentiate into neurons. These hiPSCs represent a potential resource to model CLN5 disease in a human context and investigate potential therapies.

mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria

The urea cycle enzyme argininosuccinate lyase (ASL) enables the clearance of neurotoxic ammonia and the biosynthesis of arginine. Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia and a systemic phenotype coinciding with neurocognitive impairment and chronic liver disease. Here, we describe the dysregulation of glutathione biosynthesis and upstream cysteine utilization in ASL-deficient patients and mice using targeted metabolomics and in vivo positron emission tomography (PET) imaging using (S)-4-(3-18F-fluoropropyl)-l-glutamate ([18F]FSPG). Up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways. To assess hepatic glutathione dysregulation and liver disease, we present [18F]FSPG PET as a noninvasive diagnostic tool to monitor therapeutic response in argininosuccinic aciduria. Human hASL mRNA encapsulated in lipid nanoparticles improved glutathione metabolism and chronic liver disease. In addition, hASL mRNA therapy corrected and rescued the neonatal and adult Asl-deficient mouse phenotypes, respectively, enhancing ureagenesis. These findings provide mechanistic insights in liver glutathione metabolism and support clinical translation of mRNA therapy for argininosuccinic aciduria.

Liver-directed gene therapy for inherited metabolic diseases

Gene therapy clinical trials are rapidly expanding for inherited metabolic liver diseases whilst two gene therapy products have now been approved for liver based monogenic disorders. Liver-directed gene therapy has recently become an option for treatment of haemophilias and is likely to become one of the favoured therapeutic strategies for inherited metabolic liver diseases in the near future. In this review, we present the different gene therapy vectors and strategies for liver-targeting, including gene editing. We highlight the current development of viral and nonviral gene therapy for a number of inherited metabolic liver diseases including urea cycle defects, organic acidaemias, Crigler-Najjar disease, Wilson disease, glycogen storage disease Type Ia, phenylketonuria and maple syrup urine disease. We describe the main limitations and open questions for further gene therapy development: immunogenicity, inflammatory response, genotoxicity, gene therapy administration in a fibrotic liver. The follow-up of a constantly growing number of gene therapy treated patients allows better understanding of its benefits and limitations and provides strategies to design safer and more efficacious treatments. Undoubtedly, liver-targeting gene therapy offers a promising avenue for innovative therapies with an unprecedented potential to address the unmet needs of patients suffering from inherited metabolic diseases.

Safety and efficacy of cerliponase alfa in children with neuronal ceroid lipofuscinosis type 2 (CLN2 disease): an open-label extension study

BACKGROUND

Cerliponase alfa is a recombinant human tripeptidyl peptidase 1 (TPP1) enzyme replacement therapy for the treatment of neuronal ceroid lipofuscinosis type 2 (CLN2 disease), which is caused by mutations in the TPP1 gene. We aimed to determine the long-term safety and efficacy of intracerebroventricular cerliponase alfa in children with CLN2 disease.

METHODS

This analysis includes cumulative data from a primary 48-week, single-arm, open-label, multicentre, dose-escalation study (NCT01907087) and the 240-week open-label extension with 6-month safety follow-up, conducted at five hospitals in Germany, Italy, the UK, and the USA. Children aged 3-16 years with CLN2 disease confirmed by genetic analysis and enzyme testing were eligible for inclusion. Treatment was intracerebroventricular infusion of 300 mg cerliponase alfa every 2 weeks. Historical controls with untreated CLN2 disease in the DEM-CHILD database were used as a comparator group. The primary efficacy outcome was time to an unreversed 2-point decline or score of 0 in the combined motor and language domains of the CLN2 Clinical Rating Scale. This extension study is registered with ClinicalTrials.gov, NCT02485899, and is complete.

FINDINGS

Between Sept 13, 2013, and Dec 22, 2014, 24 participants were enrolled in the primary study (15 female and 9 male). Of those, 23 participants were enrolled in the extension study, conducted between Feb 2, 2015, and Dec 10, 2020, and received 300 mg cerliponase alfa for a mean of 272·1 (range 162·1-300·1) weeks. 17 participants completed the extension and six discontinued prematurely. Treated patients were significantly less likely than historical untreated controls to have an unreversed 2-point decline or score of 0 in the combined motor and language domains (hazard ratio 0·14, 95% CI 0·06 to 0·33; p<0·0001). All participants experienced at least one adverse event and 21 (88%) experienced a serious adverse event; nine participants experienced intracerebroventricular device-related infections, with nine events in six participants resulting in device replacement. There were no study discontinuations because of an adverse event and no deaths.

INTERPRETATION

Cerliponase alfa over a mean treatment period of more than 5 years was seen to confer a clinically meaningful slowing of decline of motor and language function in children with CLN2 disease. Although our study does not have a contemporaneous control group, the results provide crucial insights into the effects of long-term treatment.

FUNDING

BioMarin Pharmaceutical.

Fetal gene therapy

Fetal gene therapy was first proposed toward the end of the 1990s when the field of gene therapy was, to quote the Gartner hype cycle, at its "peak of inflated expectations." Gene therapy was still an immature field but over the ensuing decade, it matured and is now a clinical and market reality. The trajectory of treatment for several genetic diseases is toward earlier intervention. The ability, capacity, and the will to diagnose genetic disease early-in utero-improves day by day. A confluence of clinical trials now signposts a trajectory toward fetal gene therapy. In this review, we recount the history of fetal gene therapy in the context of the broader field, discuss advances in fetal surgery and diagnosis, and explore the full ambit of preclinical gene therapy for inherited metabolic disease.

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.

Liver transplantation in ornithine transcarbamylase deficiency: A retrospective multicentre cohort study

Ornithine transcarbamylase deficiency (OTCD) is an X-linked defect of ureagenesis and the most common urea cycle disorder. Patients present with hyperammonemia causing neurological symptoms, which can lead to coma and death. Liver transplantation (LT) is the only curative therapy, but has several limitations including organ shortage, significant morbidity and requirement of lifelong immunosuppression. This study aims to identify the characteristics and outcomes of patients who underwent LT for OTCD. We conducted a retrospective study for OTCD patients from 5 UK centres receiving LT in 3 transplantation centres between 2010 and 2022. Patients' demographics, family history, initial presentation, age at LT, graft type and pre- and post-LT clinical, metabolic, and neurocognitive profile were collected from medical records. A total of 20 OTCD patients (11 males, 9 females) were enrolled in this study. 6/20 had neonatal and 14/20 late-onset presentation. 2/20 patients had positive family history for OTCD and one of them was diagnosed antenatally and received prospective treatment. All patients were managed with standard of care based on protein-restricted diet, ammonia scavengers and supplementation with arginine and/or citrulline before LT. 15/20 patients had neurodevelopmental problems before LT. The indication for LT was presence (or family history) of recurrent metabolic decompensations occurring despite standard medical therapy leading to neurodisability and quality of life impairment. Median age at LT was 10.5 months (6-24) and 66 months (35-156) in neonatal and late onset patients, respectively. 15/20 patients had deceased donor LT (DDLT) and 5/20 had living related donor LT (LDLT). Overall survival was 95% with one patient dying 6 h after LT. 13/20 had complications after LT and 2/20 patients required re-transplantation. All patients discontinued dietary restriction and ammonia scavengers after LT and remained metabolically stable. Patients who had neurodevelopmental problems before LT persisted to have difficulties after LT. 1/5 patients who was reported to have normal neurodevelopment before LT developed behavioural problems after LT, while the remaining 4 maintained their abilities without any reported issues. LT was found to be effective in correcting the metabolic defect, eliminates the risk of hyperammonemia and prolongs patients' survival.

Language Delay in Patients with CLN2 Disease: Could It Support Earlier Diagnosis?

Neuronal ceroid lipofuscinosis type 2 (CLN2 disease) is a rare pediatric disorder associated with rapid neurodegeneration, and premature death in adolescence. An effective enzyme replacement therapy (cerliponase alfa) has been approved that can reduce this predictable neurological decline. The nonspecific early symptoms of CLN2 disease frequently delay diagnosis and appropriate management. Seizures are generally recognized as the first presenting symptom of CLN2 disease, but emerging data show that language delay may precede this. An improved understanding of language deficits in the earliest stage of CLN2 disease may support the early identification of patients. In this article, CLN2 disease experts examine how language development is affected by CLN2 disease in their clinical practices. The authors' experiences highlighted the timings of first words and first use of sentences, and language stagnation as key features of language deficits in CLN2 disease, and how deficits in language may be an earlier sign of the disease than seizures. Potential challenges in identifying early language deficits include assessing patients with other complex needs, and recognizing that a child's language abilities are not within normal parameters given the variability of language development in young children. CLN2 disease should be considered in children presenting with language delay and/or seizures to facilitate earlier diagnosis and access to treatment that can significantly reduce morbidity.

Cardiac glycosides restore autophagy flux in an iPSC-derived neuronal model of WDR45 deficiency

Beta-Propeller Protein-Associated Neurodegeneration (BPAN) is one of the commonest forms of Neurodegeneration with Brain Iron Accumulation, caused by mutations in the gene encoding the autophagy-related protein, WDR45. The mechanisms linking autophagy, iron overload and neurodegeneration in BPAN are poorly understood and, as a result, there are currently no disease-modifying treatments for this progressive disorder. We have developed a patient-derived, induced pluripotent stem cell (iPSC)-based midbrain dopaminergic neuronal cell model of BPAN (3 patient, 2 age-matched controls and 2 isogenic control lines) which shows defective autophagy and aberrant gene expression in key neurodegenerative, neurodevelopmental and collagen pathways. A high content imaging-based medium-throughput blinded drug screen using the FDA-approved Prestwick library identified 5 cardiac glycosides that both corrected disease-related defective autophagosome formation and restored BPAN-specific gene expression profiles. Our findings have clear translational potential and emphasise the utility of iPSC-based modelling in elucidating disease pathophysiology and identifying targeted therapeutics for early-onset monogenic disorders.

Recapitulation of Skewed X-Inactivation in Female Ornithine Transcarbamylase-Deficient Primary Human Hepatocytes in the FRG Mouse: A Novel System for Developing Epigenetic Therapies

Realization of the immense therapeutic potential of epigenetic editing requires development of clinically predictive model systems that faithfully recapitulate relevant aspects of the target disease pathophysiology. In female patients with ornithine transcarbamylase (OTC) deficiency, an X-linked condition, skewed inactivation of the X chromosome carrying the wild-type OTC allele is associated with increased disease severity. The majority of affected female patients can be managed medically, but a proportion require liver transplantation. With rapid development of epigenetic editing technology, reactivation of silenced wild-type OTC alleles is becoming an increasingly plausible therapeutic approach. Toward this end, privileged access to explanted diseased livers from two affected female infants provided the opportunity to explore whether engraftment and expansion of dissociated patient-derived hepatocytes in the FRG mouse might produce a relevant model for evaluation of epigenetic interventions. Hepatocytes from both infants were successfully used to generate chimeric mouse-human livers, in which clusters of primary human hepatocytes were either OTC positive or negative by immunohistochemistry (IHC), consistent with clonal expansion from individual hepatocytes in which the mutant or wild-type OTC allele was inactivated, respectively. Enumeration of the proportion of OTC-positive or -negative human hepatocyte clusters was consistent with dramatic skewing in one infant and minimal to modest skewing in the other. Importantly, IHC and fluorescence-activated cell sorting analysis of intact and dissociated liver samples from both infants showed qualitatively similar patterns, confirming that the chimeric mouse-human liver model recapitulated the native state in each infant. Also of importance was the induction of a treatable metabolic phenotype, orotic aciduria, in mice, which correlated with the presence of clonally expanded OTC-negative primary human hepatocytes. We are currently using this unique model to explore CRISPR-dCas9-based epigenetic targeting strategies in combination with efficient adeno-associated virus (AAV) gene delivery to reactivate the silenced functional OTC gene on the inactive X chromosome.

Features of Congenital Arthrogryposis Due to Abnormalities in Collagen Homeostasis, a Scoping Review

Congenital arthrogryposis (CA) refers to the presence of multiple contractures at birth. It is a feature of several inherited syndromes, notable amongst them are disorders of collagen formation. This review aims to characterize disorders that directly or indirectly impact collagen structure and function leading to CA in search for common phenotypic or pathophysiological features, possible genotype-phenotype correlation, and potential novel treatment approaches based on a better understanding of the underlying pathomechanism. Nine genes, corresponding to five clinical phenotypes, were identified after a literature search. The most notable trend was the extreme phenotype variability. Clinical features across all syndromes ranged from subtle with minimal congenital contractures, to severe with multiple congenital contractures and extra-articular features including skin, respiratory, or other manifestations. Five of the identified genes were involved in the function of the Lysyl Hydroxylase 2 or 3 enzymes, which enable the hydroxylation and/or glycosylation of lysyl residues to allow the formation of the collagen superstructure. Whilst current treatment approaches are post-natal surgical correction, there are also potential in-utero therapies being developed. Cyclosporin A showed promise in treating collagen VI disorders although there is an associated risk of immunosuppression. The treatments that could be in the clinical trials soon are the splice correction therapies in collagen VI-related disorders.

Diagnostic and Management Issues in Patients with Late-Onset Ornithine Transcarbamylase Deficiency

Ornithine transcarbamylase deficiency (OTCD) is the most common inherited disorder of the urea cycle and, in general, is transmitted as an X-linked recessive trait. Defects in the OTC gene cause an impairment in ureagenesis, resulting in hyperammonemia, which is a direct cause of brain damage and death. Patients with late-onset OTCD can develop symptoms from infancy to later childhood, adolescence or adulthood. Clinical manifestations of adults with OTCD vary in acuity. Clinical symptoms can be aggravated by metabolic stressors or the presence of a catabolic state, or due to increased demands upon the urea. A prompt diagnosis and relevant biochemical and genetic investigations allow the rapid introduction of the right treatment and prevent long-term complications and mortality. This narrative review outlines challenges in diagnosing and managing patients with late-onset OTCD.

Genetic Therapy Approaches for Ornithine Transcarbamylase Deficiency

Ornithine transcarbamylase deficiency (OTCD) is the most common urea cycle disorder with high unmet needs, as current dietary and medical treatments may not be sufficient to prevent hyperammonemic episodes, which can cause death or neurological sequelae. To date, liver transplantation is the only curative choice but is not widely available due to donor shortage, the need for life-long immunosuppression and technical challenges. A field of research that has shown a great deal of promise recently is gene therapy, and OTCD has been an essential candidate for different gene therapy modalities, including AAV gene addition, mRNA therapy and genome editing. This review will first summarise the main steps towards clinical translation, highlighting the benefits and challenges of each gene therapy approach, then focus on current clinical trials and finally outline future directions for the development of gene therapy for OTCD.

New Perspectives in Dried Blood Spot Biomarkers for Lysosomal Storage Diseases

Dried blood spots (DBSs) biomarkers are convenient for monitoring for specific lysosomal storage diseases (LSDs), but they could have relevance for other LSDs. To determine the specificity and utility of glycosphingolipidoses biomarkers against other LSDs, we applied a multiplexed lipid liquid chromatography tandem mass spectrometry assay to a DBS cohort of healthy controls (n = 10) and Gaucher (n = 4), Fabry (n = 10), Pompe (n = 2), mucopolysaccharidosis types I-VI (n = 52), and Niemann-Pick disease type C (NPC) (n = 5) patients. We observed no complete disease specificity for any of the markers tested. However, comparison among the different LSDs highlighted new applications and perspectives of the existing biomarkers. We observed elevations in glucosylceramide isoforms in the NPC and Gaucher patients relative to the controls. In NPC, there was a greater proportion of C24 isoforms, giving a specificity of 96-97% for NPC, higher than 92% for the NPC biomarker N-palmitoyl-O-phosphocholineserine ratio to lyso-sphingomyelin. We also observed significantly elevated levels of lyso-dihexosylceramide in Gaucher and Fabry disease as well as elevated lyso-globotriaosylceramide (Lyso-Gb3) in Gaucher disease and the neuronopathic forms of Mucopolysaccharidoses. In conclusion, DBS glucosylceramide isoform profiling has increased the specificity for the detection of NPC, thereby improving diagnostic accuracy. Low levels of lyso-lipids can be observed in other LSDs, which may have implications in their disease pathogenesis.

Natural history of epilepsy in argininosuccinic aciduria provides new insights into pathophysiology: A retrospective international study

OBJECTIVE

Argininosuccinate lyase (ASL) is integral to the urea cycle, which enables nitrogen wasting and biosynthesis of arginine, a precursor of nitric oxide. Inherited ASL deficiency causes argininosuccinic aciduria, the second most common urea cycle defect and an inherited model of systemic nitric oxide deficiency. Patients present with developmental delay, epilepsy, and movement disorder. Here we aim to characterize epilepsy, a common and neurodebilitating comorbidity in argininosuccinic aciduria.

METHODS

We conducted a retrospective study in seven tertiary metabolic centers in the UK, Italy, and Canada from 2020 to 2022, to assess the phenotype of epilepsy in argininosuccinic aciduria and correlate it with clinical, biochemical, radiological, and electroencephalographic data.

RESULTS

Thirty-seven patients, 1-31 years of age, were included. Twenty-two patients (60%) presented with epilepsy. The median age at epilepsy onset was 24 months. Generalized tonic-clonic and focal seizures were most common in early-onset patients, whereas atypical absences were predominant in late-onset patients. Seventeen patients (77%) required antiseizure medications and six (27%) had pharmacoresistant epilepsy. Patients with epilepsy presented with a severe neurodebilitating disease with higher rates of speech delay (p = .04) and autism spectrum disorders (p = .01) and more frequent arginine supplementation (p = .01) compared to patients without epilepsy. Neonatal seizures were not associated with a higher risk of developing epilepsy. Biomarkers of ureagenesis did not differ between epileptic and non-epileptic patients. Epilepsy onset in early infancy (p = .05) and electroencephalographic background asymmetry (p = .0007) were significant predictors of partially controlled or refractory epilepsy.

SIGNIFICANCE

Epilepsy in argininosuccinic aciduria is frequent, polymorphic, and associated with more frequent neurodevelopmental comorbidities. We identified prognostic factors for pharmacoresistance in epilepsy. This study does not support defective ureagenesis as prominent in the pathophysiology of epilepsy but suggests a role of central dopamine deficiency. A role of arginine in epileptogenesis was not supported and warrants further studies to assess the potential arginine neurotoxicity in argininosuccinic aciduria.

Genomic investigations of unexplained acute hepatitis in children

Since its first identification in Scotland, over 1,000 cases of unexplained paediatric hepatitis in children have been reported worldwide, including 278 cases in the UK1. Here we report an investigation of 38 cases, 66 age-matched immunocompetent controls and 21 immunocompromised comparator participants, using a combination of genomic, transcriptomic, proteomic and immunohistochemical methods. We detected high levels of adeno-associated virus 2 (AAV2) DNA in the liver, blood, plasma or stool from 27 of 28 cases. We found low levels of adenovirus (HAdV) and human herpesvirus 6B (HHV-6B) in 23 of 31 and 16 of 23, respectively, of the cases tested. By contrast, AAV2 was infrequently detected and at low titre in the blood or the liver from control children with HAdV, even when profoundly immunosuppressed. AAV2, HAdV and HHV-6 phylogeny excluded the emergence of novel strains in cases. Histological analyses of explanted livers showed enrichment for T cells and B lineage cells. Proteomic comparison of liver tissue from cases and healthy controls identified increased expression of HLA class 2, immunoglobulin variable regions and complement proteins. HAdV and AAV2 proteins were not detected in the livers. Instead, we identified AAV2 DNA complexes reflecting both HAdV-mediated and HHV-6B-mediated replication. We hypothesize that high levels of abnormal AAV2 replication products aided by HAdV and, in severe cases, HHV-6B may have triggered immune-mediated hepatic disease in genetically and immunologically predisposed children.

Targeting the liver to treat the eye

Over the last two decades, gene therapy has given hope of potential cure for many rare diseases. In the simplest form, gene therapy is the transfer or editing of a genetic material to cure a disease via nonviral or viral vehicles. Gene therapy can be performed either in vivo by injecting a vector carrying the gene or tools for gene editing directly into a tissue or into the systemic circulation, or ex vivo when patient cells are genetically modified outside of the body and then introduced back into the patient (Yilmaz et al, 2022). Adeno-associated viral vectors (AAV) have been the vectors of choice for in vivo gene therapy. There has been a lot of promising research on the development of novel tissue and cell-specific serotypes in order to improve efficacy and safety for clinical applications (Kuzmin et al, 2021). In this issue of EMBO Molecular Medicine, Boffa and colleagues present a novel AAV-based liver-directed gene therapy for ornithine aminotransferase deficiency.

Atidarsagene autotemcel for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare autosomal recessive disorder of sphingolipid metabolism, due to a deficiency of the enzyme arylsulfatase A (ARSA). The main clinical signs of the disease are secondary to central and peripheral nervous system demyelination. MLD is subdivided into early- and late-onset subtypes based upon the onset of neurological disease. The early-onset subtype is associated with a more rapid progression of the disease that leads to death within the first decade of life. Until recently, no effective treatment was available for MLD. The blood-brain barrier (BBB) prevents systemically administered enzyme replacement therapy from reaching target cells in MLD. The evidence for the efficacy of hematopoietic stem cell transplantation is limited to the late-onset MLD subtype. Here, we review the preclinical and clinical studies that facilitated the approval of the ex vivo gene therapy atidarsagene autotemcel for early-onset MLD by the European Medicines Agency (EMA) in December 2020. This approach was studied in an animal model first and then in a clinical trial, eventually proving its efficacy in preventing disease manifestations in presymptomatic patients and stabilizing its progression in paucisymptomatic subjects. This new therapeutic consists of patients' CD34+ hematopoietic stem/progenitor cells (HSPCs) transduced with a lentiviral vector encoding functional ARSA cDNA. The gene-corrected cells get reinfused into the patients after a cycle of chemotherapy conditioning.

Buffy Coat Score as a Biomarker of Treatment Response in Neuronal Ceroid Lipofuscinosis Type 2

The introduction of intracerebroventricular (ICV) enzyme replacement therapy (ERT) for treatment of neuronal ceroid lipofuscinosis type 2 (CLN2) disease has produced dramatic improvements in disease management. However, assessments of therapeutic effect for ICV ERT are limited to clinical observational measures, namely the CLN2 Clinical Rating Scale, a subjective measure of motor and language performance. There is a need for an objective biomarker to enable assessments of disease progression and response to treatment. To address this, we investigated whether the proportion of cells with abnormal storage inclusions on electron microscopic examination of peripheral blood buffy coats could act as a biomarker of disease activity in CLN2 disease. We conducted a prospective longitudinal analysis of six patients receiving ICV ERT. We demonstrated a substantial and continuing reduction in the proportion of abnormal cells over the course of treatment, whereas symptomatic scores revealed little or no change over time. Here, we proposed the use of the proportion of cells with abnormal storage as a biomarker of response to therapy in CLN2. In the future, as more tissue-specific biomarkers are developed, the buffy coats may form part of a panel of biomarkers in order to give a more holistic view of a complex disease.

Niemann-Pick type C disease as proof-of-concept for intelligent biomarker panel selection in neurometabolic disorders

AIM

Using Niemann-Pick type C disease (NPC) as a paradigm, we aimed to improve biomarker discovery in patients with neurometabolic disorders.

METHOD

Using a multiplexed liquid chromatography tandem mass spectrometry dried bloodspot assay, we developed a selective intelligent biomarker panel to monitor known biomarkers N-palmitoyl-O-phosphocholineserine and 3β,5α,6β-trihydroxy-cholanoyl-glycine as well as compounds predicted to be affected in NPC pathology. We applied this panel to a clinically relevant paediatric patient cohort (n = 75; 35 males, 40 females; mean age 7 years 6 months, range 4 days-19 years 8 months) presenting with neurodevelopmental and/or neurodegenerative pathology, similar to that observed in NPC.

RESULTS

The panel had a far superior performance compared with individual biomarkers. Namely, NPC-related established biomarkers used individually had 91% to 97% specificity but the combined panel had 100% specificity. Moreover, multivariate analysis revealed long-chain isoforms of glucosylceramide were elevated and very specific for patients with NPC.

INTERPRETATION

Despite advancements in next-generation sequencing and precision medicine, neurological non-enzymatic disorders remain difficult to diagnose and lack robust biomarkers or routine functional testing for genetic variants of unknown significance. Biomarker panels may have better diagnostic accuracy than individual biomarkers in neurometabolic disorders, hence they can facilitate more prompt disease identification and implementation of emerging targeted, disease-specific therapies.

WHAT THIS PAPER ADDS

Intelligent biomarker panel design can help expedite diagnosis in neurometabolic disorders. In Niemann-Pick type C disease, such a panel performed better than individual biomarkers. Biomarker panels are easy to implement and widely applicable to neurometabolic conditions.

Three-Country Snapshot of Ornithine Transcarbamylase Deficiency

X-linked ornithine transcarbamylase deficiency (OTCD) is the most common urea cycle defect. The disease severity ranges from asymptomatic carrier state to severe neonatal presentation with hyperammonaemic encephalopathy. We audited the diagnosis and management of OTCD, using an online 12-question-survey that was sent to 75 metabolic centres in Turkey, France and the UK. Thirty-nine centres responded and 495 patients were reported in total. A total of 208 French patients were reported, including 71 (34%) males, 86 (41%) symptomatic and 51 (25%) asymptomatic females. Eighty-five Turkish patients included 32 (38%) males, 39 (46%) symptomatic and 14 (16%) asymptomatic females. Out of the 202 UK patients, 66 (33%) were male, 83 (41%) asymptomatic and 53 (26%) symptomatic females. A total of 19%, 12% and 7% of the patients presented with a neonatal-onset phenotype in France, Turkey and the UK, respectively. Vomiting, altered mental status and encephalopathy were the most common initial symptoms in all three countries. While 69% in France and 79% in Turkey were receiving protein restriction, 42% were on a protein-restricted diet in the UK. A total of 76%, 47% and 33% of patients were treated with ammonia scavengers in Turkey, France and the UK, respectively. The findings of our audit emphasize the differences and similarities in manifestations and management practices in three countries.

The ultrastructural organization of endoplasmic reticulum-plasma membrane contacts is conserved in epithelial cells

Contacts between the endoplasmic reticulum and the plasma membrane (ER-PM contacts) have important roles in membrane lipid and calcium dynamics, yet their organization in polarized epithelial cells has not been thoroughly described. Here we examine ER-PM contacts in hepatocytes in mouse liver using electron microscopy, providing the first comprehensive ultrastructural study of ER-PM contacts in a mammalian epithelial tissue. Our quantitative analyses reveal strikingly distinct ER-PM contact architectures spatially linked to apical, lateral, and basal PM domains. Notably, we find that an extensive network of ER-PM contacts exists at lateral PM domains that form intercellular junctions between hepatocytes. Moreover, the spatial organization of ER-PM contacts is conserved in epithelial spheroids, suggesting that ER-PM contacts may serve conserved roles in epithelial cell architecture. Consistent with this notion, we show that ORP5 activity at ER-PM contacts modulates the apical-basolateral aspect ratio in HepG2 cells. Thus ER-PM contacts have a conserved distribution and crucial roles in PM domain architecture across epithelial cell types.

Neurocognitive outcome and mental health in children with tyrosinemia type 1 and phenylketonuria: A comparison between two genetic disorders affecting the same metabolic pathway

Tyrosinemia type 1 (TT1) and phenylketonuria (PKU) are both inborn errors of phenylalanine-tyrosine metabolism. Neurocognitive and behavioral outcomes have always featured in PKU research but received less attention in TT1 research. This study aimed to investigate and compare neurocognitive, behavioral, and social outcomes of treated TT1 and PKU patients. We included 33 TT1 patients (mean age 11.24 years; 16 male), 31 PKU patients (mean age 10.84; 14 male), and 58 age- and gender-matched healthy controls (mean age 10.82 years; 29 male). IQ (Wechsler-subtests), executive functioning (the Behavioral Rating Inventory of Executive Functioning), mental health (the Achenbach-scales), and social functioning (the Social Skills Rating System) were assessed. Results of TT1 patients, PKU patients, and healthy controls were compared using Kruskal-Wallis tests with post-hoc Mann-Whitney U tests. TT1 patients showed a lower IQ and poorer executive functioning, mental health, and social functioning compared to healthy controls and PKU patients. PKU patients did not differ from healthy controls regarding these outcome measures. Relatively poor outcomes for TT1 patients were particularly evident for verbal IQ, BRIEF dimensions "working memory", "plan and organize" and "monitor", ASEBA dimensions "social problems" and "attention problems", and for the SSRS "assertiveness" scale (all p values <0.001). To conclude, TT1 patients showed cognitive impairments on all domains studied, and appeared to be significantly more affected than PKU patients. More attention should be paid to investigating and monitoring neurocognitive outcome in TT1 and research should focus on explaining the underlying pathophysiological mechanism.

Pathological structural conversion of α-synuclein at the mitochondria induces neuronal toxicity

Aggregation of alpha-synuclein (α-Syn) drives Parkinson's disease (PD), although the initial stages of self-assembly and structural conversion have not been directly observed inside neurons. In this study, we tracked the intracellular conformational states of α-Syn using a single-molecule Förster resonance energy transfer (smFRET) biosensor, and we show here that α-Syn converts from a monomeric state into two distinct oligomeric states in neurons in a concentration-dependent and sequence-specific manner. Three-dimensional FRET-correlative light and electron microscopy (FRET-CLEM) revealed that intracellular seeding events occur preferentially on membrane surfaces, especially at mitochondrial membranes. The mitochondrial lipid cardiolipin triggers rapid oligomerization of A53T α-Syn, and cardiolipin is sequestered within aggregating lipid-protein complexes. Mitochondrial aggregates impair complex I activity and increase mitochondrial reactive oxygen species (ROS) generation, which accelerates the oligomerization of A53T α-Syn and causes permeabilization of mitochondrial membranes and cell death. These processes were also observed in induced pluripotent stem cell (iPSC)-derived neurons harboring A53T mutations from patients with PD. Our study highlights a mechanism of de novo α-Syn oligomerization at mitochondrial membranes and subsequent neuronal toxicity.

Three-dimensional Characterization of Interorganelle Contact Sites in Hepatocytes using Serial Section Electron Microscopy

Transmission electron microscopy has been long considered to be the gold standard for the visualization of cellular ultrastructure. However, analysis is often limited to two dimensions, hampering the ability to fully describe the three-dimensional (3D) ultrastructure and functional relationship between organelles. Volume electron microscopy (vEM) describes a collection of techniques that enable the interrogation of cellular ultrastructure in 3D at mesoscale, microscale, and nanoscale resolutions. This protocol provides an accessible and robust method to acquire vEM data using serial section transmission EM (TEM) and covers the technical aspects of sample processing through to digital 3D reconstruction in a single, straightforward workflow. To demonstrate the usefulness of this technique, the 3D ultrastructural relationship between the endoplasmic reticulum and mitochondria and their contact sites in liver hepatocytes is presented. Interorganelle contacts serve vital roles in the transfer of ions, lipids, nutrients, and other small molecules between organelles. However, despite their initial discovery in hepatocytes, there is still much to learn about their physical features, dynamics, and functions. Interorganelle contacts can display a range of morphologies, varying in the proximity of the two organelles to one another (typically ~10-30 nm) and the extent of the contact site (from punctate contacts to larger 3D cisternal-like contacts). The examination of close contacts requires high-resolution imaging, and serial section TEM is well suited to visualize the 3D ultrastructural of interorganelle contacts during hepatocyte differentiation, as well as alterations in hepatocyte architecture associated with metabolic diseases.

Cerebrospinal fluid neurofilament light chain levels in CLN2 disease patients treated with enzyme replacement therapy normalise after two years on treatment

Classic late infantile neuronal ceroid lipofuscinosis (CLN2 disease) is caused by a deficiency of tripeptidyl-peptidase-1. In 2017, the first CLN2 enzyme replacement therapy (ERT) cerliponase alfa (Brineura) was approved by the FDA and EMA. The CLN2 disease clinical rating scale (CLN2 CRS) was developed to monitor loss of motor function, language and vision as well as frequency of generalised tonic clonic seizures. Using CLN2 CRS in an open label clinical trial it was shown that Brineura slowed down the progression of CLN2 symptoms.

Neurofilament light chain (NfL) is a protein highly expressed in myelinated axons. An increase of cerebrospinal fluid (CSF) and blood NfL is found in a variety of neuroinflammatory, neurodegenerative, traumatic, and cerebrovascular diseases. We analysed CSF NfL in CLN2 patients treated with Brineura to establish whether it can be used as a possible biomarker of response to therapy. Newly diagnosed patients had CSF samples collected and analysed at first treatment dose and up to 12 weeks post-treatment to look at acute changes. Patients on a compassionate use programme who were already receiving ERT for approximately 1yr had CSF samples collected and NfL analysed over the following 1.3 years (2.3 years post-initiation of ERT) to look at long-term changes.

All newly diagnosed patients we investigated with classical late infantile phenotype had high NfL levels >2000 pg/ml at start of treatment. No significant change was observed in NfL up to 12 weeks post-treatment. After one year of ERT, two out of six patients still had high NfL levels, but all patients showed a continued decrease, and all had low NfL levels after two years on ERT. NfL levels appear to correspond and predict improved clinical status of patients on ERT and could be useful as a biomarker to monitor neurodegeneration and verify disease modification in CLN2 patients on ERT.

Clinical disease characteristics of patients with Niemann-Pick Disease Type C: findings from the International Niemann-Pick Disease Registry (INPDR)

Background

Niemann-Pick Disease Type C (NPC) is an autosomal recessive rare disease characterised by progressive neurovisceral manifestations. The collection of on-going large-scale NPC clinical data may generate better understandings of the natural history of the disease. Here we report NPC patient data from the International Niemann-Pick Disease Registry (INPDR).

Method

The INPDR is a web-based, patient-led independent registry for the collection of prospective and retrospective clinical data from Niemann-Pick Disease patients. Baseline data from NPC patients enrolled into the INPDR from September 2014 to December 2019 was extracted to analyse the demographic, genetic and clinical features of the disease.

Results

A total of 203 NPC patients from six European countries were included in this study. The mean age (SD) at diagnosis was 11.2 years (14.2). Among enrolled patients, 168 had known neurological manifestations: 43 (24.2%) had early-infantile onset, 47 (26.4%) had late-infantile onset, 41 (23.0%) had juvenile onset, and 37 (20.8%) had adult onset. 10 (5.6%) patients had the neonatal rapidly fatal systemic form. Among the 97 patients with identified NPC1 variants, the most common variant was the c. 3182T > C variant responsible for the p.lle1061Thr protein change, reported in 35.1% (N = 34) of patients. The frequencies of hepatomegaly and neonatal jaundice were greatest in patients with early-infantile and late-infantile neurological onset. Splenomegaly was the most commonly reported observation, including 80% of adult-onset patients. The most commonly reported neurological manifestations were cognitive impairment (78.5%), dysarthria (75.9%), ataxia (75.9%), vertical supranuclear gaze palsy (70.9%) and dysphagia (69.6%). A 6-domain composite disability scale was used to calculate the overall disability score for each neurological form. Across all with neurological onset, the majority of patients showed moderate to severe impairments in all domains, except for ‘swallowing’ and ‘seizure’. The age at diagnosis and death increased with increased age of neurological symptom onset. Miglustat use was recorded in 62.4% of patients and the most common symptomatic therapies used by patients were antiepileptics (32.9%), antidepressants (11.8%) and antacids (9.4%).

Conclusion

The proportion of participants at each age of neurological onset was relatively equal across the cohort. Neurological manifestations, such as ataxia, dysphagia, and dysarthria, were frequently observed across all age categories.

A survival analysis of ventricular access devices for delivery of cerliponase alfa

OBJECTIVE

Late infantile neuronal ceroid lipofuscinosis type 2 (CLN2) is a rare autosomal recessive disease caused by tripeptidyl peptidase 1 enzyme deficiency. At the authors' center, the medication cerliponase alfa is administered every 2 weeks via the intracerebroventricular (ICV) route. This requires the placement of a ventricular access device (VAD) or reservoir and frequent percutaneous punctures of this device over the child's lifetime. In this study, the authors audited the longevity and survival of these VADs and examined the causes of device failure.

METHODS

A single-center survival analysis of VAD insertions and revisions (January 2014 through June 2020) was conducted. All children received cerliponase alfa infusions through a VAD. Patient characteristics and complications were determined from a prospectively maintained surgical database and patient records. For the VAD survival analysis, the defined endpoint was when the device was removed or changed. Reservoir survival was assessed using Kaplan-Meier curves and the log-rank (Cox-Mantel) test.

RESULTS

A total of 17 patients had VADs inserted for drug delivery; median (range) age at first surgery was 4 years 4 months (1 year 8 months to 15 years). Twenty-six VAD operations (17 primary insertions and 9 revisions) were required among these 17 patients. Twelve VAD operations had an associated complication, including CSF infection (n = 6) with Propionibacterium and Staphylococcus species being the most prevalent organisms, significant surgical site swelling preventing infusion (n = 3), leakage/wound breakdown (n = 2), and catheter obstruction (n = 1). There were no complications or deaths associated with VAD insertion. The median (interquartile range) number of punctures was 59.5 (7.5-82.0) for unrevised VADs (n = 17) versus 2 (6-87.5) for revised VADs (n = 9) (p = 0.70). The median survival was 301 days for revisional reservoirs (n = 9) versus 2317 days for primary inserted reservoirs (n = 17) (p = 0.019).

CONCLUSIONS

In the context of the current interest in intrathecal drug delivery for rare metabolic disorders, the need for VADs is likely to increase. Auditing the medium- to long-term outcomes associated with these devices will hopefully result in their wider application and may have potential implications on the development of new VAD technologies. These results could also be used to counsel parents prior to commencement of therapy and VAD implantation.

Safety and efficacy of an engineered hepatotropic AAV gene therapy for ornithine transcarbamylase deficiency in cynomolgus monkeys

X-linked inherited ornithine transcarbamylase deficiency (OTCD) is the most common disorder affecting the liver-based urea cycle, a pathway enabling detoxification of nitrogen waste and endogenous arginine biosynthesis. Patients develop acute hyperammonemia leading to neurological sequelae or death despite the best-accepted therapy based on ammonia scavengers and protein-restricted diet. Liver transplantation is curative but associated with procedure-related complications and lifelong immunosuppression. Adeno-associated viral (AAV) vectors have demonstrated safety and clinical benefits in a rapidly growing number of clinical trials for inherited metabolic liver diseases. Engineered AAV capsids have shown promising enhanced liver tropism. Here, we conducted a good-laboratory practice-compliant investigational new drug-enabling study to assess the safety of intravenous liver-tropic AAVLK03 gene transfer of a human codon-optimized OTC gene. Juvenile cynomolgus monkeys received vehicle and a low and high dose of vector (2 × 1012 and 2 × 1013 vector genome (vg)/kg, respectively) and were monitored for 26 weeks for in-life safety with sequential liver biopsies at 1 and 13 weeks post-vector administration. Upon completion of monitoring, animals were euthanized to study vector biodistribution, immune responses, and histopathology. The product was well tolerated with no adverse clinical events, predominant hepatic biodistribution, and sustained supra-physiological OTC overexpression. This study supports the clinical deployment of intravenous AAVLK03 for severe OTCD.

The Genetics of Inherited Cholestatic Disorders in Neonates and Infants: Evolving Challenges

Many inherited conditions cause cholestasis in the neonate or infant. Next-generation sequencing methods can facilitate a prompt diagnosis in some of these cases; application of these methods in patients with liver diseases of unknown cause has also uncovered novel gene-disease associations and improved our understanding of physiological bile secretion and flow. By helping to define the molecular basis of certain cholestatic disorders, these methods have also identified new targets for therapy as well patient subgroups more likely to benefit from specific therapies. At the same time, sequencing methods have presented new diagnostic challenges, such as the interpretation of single heterozygous genetic variants. This article discusses those challenges in the context of neonatal and infantile cholestasis, focusing on difficulties in predicting variant pathogenicity, the possibility of other causal variants not identified by the genetic screen used, and phenotypic variability among patients with variants in the same genes. A prospective, observational study performed between 2010-2013, which sequenced six important genes (ATP8B1, ABCB11, ABCB4, NPC1, NPC2 and SLC25A13) in an international cohort of 222 patients with infantile liver disease, is given as an example of potential benefits and challenges that clinicians could face having received a complex genetic result. Further studies including large cohorts of patients with paediatric liver disease are needed to clarify the spectrum of phenotypes associated with, as well as appropriate clinical response to, single heterozygous variants in cholestasis-associated genes.

Rab35 controls formation of luminal projections required for bile canalicular morphogenesis

Hepatocytes display a unique biaxial polarity with shared apical luminal connections between adjacent hepatocytes that merge into a network of bile canaliculi. Belicova et al. (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202103003) discovered that hepatocyte apical membranes generate Rab35-dependent extensions that traverse the lumen and are essential for bile canalicular formation and maintenance.

A Case Series on Genotype and Outcome of Liver Transplantation in Children with Niemann-Pick Disease Type C

BACKGROUND

To report on clinical presentation and outcomes of children who underwent liver transplantation (LTx) and were subsequently diagnosed to have Niemann-Pick type C (NPC).

METHODS

Retrospective, descriptive, multi-centre review of children diagnosed with NPC who underwent LTx (2003-2018). Diagnosis was made by filipin skin test or genetic testing.

RESULTS

Nine children were identified (six centres). Neonatal acute liver failure was the most common indication for LTx (seven children). Median age at first presentation: 7 days (range: 0-37). The most prevalent presenting symptoms: jaundice (8/9), hepatosplenomegaly (8/9) and ascites (6/9). 8/9 children had a LTx before the diagnosis of NPC. Genetic testing revealed mutations in NPC1 correlating with a severe biochemical phenotype in 5 patients. All 9 children survived beyond early infancy. Seven children are still alive (median follow-up time of 9 (range: 6-13) years). Neurological symptoms developed in 4/7 (57%) patients at median 9 (range: 5-13) years following LTx.

CONCLUSION

Early diagnosis of NPC continues to be a challenge and a definitive diagnosis is often made only after LTx. Neurological disease is not prevented in the majority of patients. Genotype does not appear to predict neurological outcome after LTx. LTx still remains controversial in NPC.

An ERG and OCT study of neuronal ceroid lipofuscinosis CLN2 Battens retinopathy

BACKGROUND

Late infantile neuronal ceroid lipofuscinosis (CLN2 Batten disease) is a rare, progressive neurodegenerative disease of childhood. The natural history of motor and language regression is used to monitor the efficacy of CNS treatments. Less is known about CLN2 retinopathy. Our aim is to elaborate the nature, age of onset, and symmetry of CLN2 retinopathy using visual electrophysiology and ophthalmic imaging.

SUBJECTS AND METHODS

We reviewed 22 patients with genetically confirmed CLN2 disease; seventeen showing classical and five atypical disease. Flash electroretinograms (ERGs), flash and pattern reversal visual evoked potentials (VEPs), recorded from awake children were collated. Available fundus images were graded, optical coherence tomography (OCT) central subfoveal thickness (CST) measured, and genotype, age, clinical vision assessment and motor language grades assembled.

RESULTS

ERGs show cone/rod system dysfunction preceded by localised macular ellipsoid zone disruption on OCT from 4.8 years. Electroencephalogram (EEG) time-locked spikes confounded both pattern 6/17 (35%) and flash VEPs 12/16 (75%). Paired right eye (RE) and left eye (LE) ERG amplitudes did not differ significantly for each flash stimulus at the p 0.001 level, Wilcoxon ranked signed test. Cone ERGs show a functional deficit before CST thinning in classical disease. Optomap hyper fundus autofluorescence (FAF) at the fovea was noted in three patients with normal ERGs. The oldest patient showed an ovoid aggregate above the external limiting membrane at the fovea, which did not affect the PERG.

CONCLUSION

ERG findings in CLN2 retinopathy show symmetrical cone-rod dysfunction, from 4y10m in this series, but a broad range of ages when ERG function is preserved.

Efficacy and safety of N-acetyl-L-leucine in Niemann-Pick disease type C

OBJECTIVE

To investigate the safety and efficacy of N-acetyl-L-leucine (NALL) on symptoms, functioning, and quality of life in pediatric (≥ 6 years) and adult Niemann-Pick disease type C (NPC) patients.

METHODS

In this multi-national, open-label, rater-blinded Phase II study, patients were assessed during a baseline period, a 6-week treatment period (orally administered NALL 4 g/day in patients ≥ 13 years, weight-tiered doses for patients 6-12 years), and a 6-week post-treatment washout period. The primary Clinical Impression of Change in Severity (CI-CS) endpoint (based on a 7-point Likert scale) was assessed by blinded, centralized raters who compared randomized video pairs of each patient performing a pre-defined primary anchor test (8-Meter Walk Test or 9-Hole Peg Test) during each study periods. Secondary outcomes included cerebellar functional rating scales, clinical global impression, and quality of life assessments.

RESULTS

33 subjects aged 7-64 years with a confirmed diagnosis of NPC were enrolled. 32 patients were included in the primary modified intention-to-treat analysis. NALL met the CI-CS primary endpoint (mean difference 0.86, SD = 2.52, 90% CI 0.25, 1.75, p = 0.029), as well as secondary endpoints. No treatment-related serious adverse events occurred.

CONCLUSIONS

NALL demonstrated a statistically significant and clinical meaningfully improvement in symptoms, functioning, and quality of life in 6 weeks, the clinical effect of which was lost after the 6-week washout period. NALL was safe and well-tolerated, informing a favorable benefit-risk profile for the treatment of NPC. CLINICALTRIALS.

GOV IDENTIFIER

NCT03759639.

Diagnosing Mitochondrial Disorders Remains Challenging in the Omics Era

Objective

We hypothesized that novel investigative pathways are needed to decrease diagnostic odysseys in pediatric mitochondrial disease and sought to determine the utility of clinical exome sequencing in a large cohort with suspected mitochondrial disease and to explore whether any of the traditional indicators of mitochondrial disease predict a confirmed genetic diagnosis.

Methods

We investigated a cohort of 85 pediatric patients using clinical exome sequencing and compared the results with the outcome of traditional diagnostic tests, including biochemical testing of routine parameters (lactate, alanine, and proline), neuroimaging, and muscle biopsy with histology and respiratory chain enzyme activity studies.

Results

We established a genetic diagnosis in 36.5% of the cohort and report 20 novel disease-causing variants (1 mitochondrial DNA). Counterintuitively, routine biochemical markers were more predictive of mitochondrial disease than more invasive and elaborate muscle studies.

Conclusions

We propose using biochemical markers to support the clinical suspicion of mitochondrial disease and then apply first-line clinical exome sequencing to identify a definite diagnosis. Muscle biopsy studies should only be used in clinically urgent situations or to confirm an inconclusive genetic result.

Classification of Evidence

This is a Class II diagnostic accuracy study showing that the combination of CSF and plasma biochemical tests plus neuroimaging could predict the presence or absence of exome sequencing confirmed mitochondrial disorders.

Investigating health-related quality of life in rare diseases: a case study in utility value determination for patients with CLN2 disease (neuronal ceroid lipofuscinosis type 2)

Background

Utility studies enable preference-based quantification of a disease’s impact on patients’ health-related quality of life (HRQoL). It is often difficult to obtain utility values for rare, neurodegenerative conditions due to cognitive burden of direct elicitation methods, and the limited size of patient/caregiver populations. CLN2 disease (neuronal ceroid lipofuscinosis type 2) is an ultra-rare, progressive condition, for which there are no published utility data fully capturing all disease stages. This case study demonstrates how utility values can be estimated for ultra-rare paediatric diseases by asking clinicians to complete EQ-5D-5L questionnaires based on vignettes describing the stages of CLN2 disease.

Methods

An indirect elicitation method using proxy-reporting by clinical experts was adopted. Eighteen vignettes were developed, describing nine progressive disease stages as defined by motor and language domain scores of the CLN2 Clinical Rating Scale, in individuals treated with cerliponase alfa or standard care. Eight clinical experts with experience of treating CLN2 disease with cerliponase alfa and current standard care completed the proxy version 2 EQ-5D-5L online after reading these vignettes. Resulting scores were converted to EQ-5D-5L utility values for each disease stage, using UK, German and Spanish value sets.

Results

Utility values, which are typically anchored by 0 (equivalent to death) and 1 (full health), decreased with CLN2 disease progression (results spanned the maximum range of the utility scale). Assigned utility values were consistently higher for patients receiving cerliponase alfa than standard care; differences were statistically significant for the 6 most severe disease stages (p < 0.05). Analysis of the individual dimensions of the EQ-5D-5L showed that greatest differences between patients treated with cerliponase alfa and standard care occurred in the pain dimension (differences in mean scores ranged between no difference and 1.8), with notable differences also observed in the anxiety/depression dimension (differences in mean scores ranged between 0.1 and 1.0).

Conclusions

This study demonstrates a feasible methodology for eliciting utility values in CLN2 disease, indicating HRQoL declines with disease progression. Vignettes describing patients receiving cerliponase alfa were consistently assigned higher utility values for the same disease state, suggesting this treatment improves HRQoL compared with standard care.

Trial registration NCT01907087, NCT02485899.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01829-x.

Clinical applications for exosomes: Are we there yet?

Exosomes are a subset of extracellular vesicles essential for cell-cell communication in health and disease with the ability to transport nucleic acids, functional proteins and other metabolites. Their clinical use as diagnostic biomarkers and therapeutic carriers has become a major field of research over recent years, generating rapidly expanding scientific interest and financial investment. Their reduced immunogenicity compared to liposomes or viral vectors and their ability to cross major physiological barriers like the blood-brain barrier make them an appealing and innovative option as biomarkers and therapeutic agents. Here, we review the latest clinical developments of exosome biotechnology for diagnostic and therapeutic purposes, including the most recent COVID-19-related exosome-based clinical trials. We present current exosome engineering strategies for optimal clinical safety and efficacy, and assess the technology developed for good manufacturing practice compliant scaling up and storage approaches along with their limitations in pharmaceutical industry.

Cerliponase Alfa for the Treatment of Atypical Phenotypes of CLN2 Disease: A Retrospective Case Series

BACKGROUND

The classic phenotype of CLN2 disease (neuronal ceroid lipofuscinosis type 2) typically manifests between ages 2 and 4 years with a predictable clinical course marked by epilepsy, language developmental delay, and rapid psychomotor decline. Atypical phenotypes exhibit variable time of onset, symptomatology, and/or progression. Intracerebroventricular-administered cerliponase alfa (rhTPP1 enzyme) has been shown to stabilize motor and language function loss in patients with classic CLN2 disease, but its impact on individuals with atypical phenotypes has not been described.

METHODS

A chart review was conducted of 14 patients (8 male, 6 female) with atypical CLN2 phenotypes who received cerliponase alfa. Pre- and posttreatment CLN2 Clinical Rating Scale Motor and Language (ML) domain scores were compared.

RESULTS

Median age at first presenting symptom was 5.9 years. First reported symptoms were language abnormalities (6 [43%] patients), seizures (4 [29%]), ataxia/language abnormalities (3 [21%]), and ataxia alone (1 [7%]). Median age at diagnosis was 10.8 years. ML score declined before treatment in 13 (93%) patients. Median age at treatment initiation was 11.7 years; treatment duration ranged from 11 to 58 months. From treatment start, ML score remained stable in 11 patients (treatment duration 11-43 months), improved 1 point in 1 patient after 13 months, and declined 1 point in 2 patients after 15 and 58 months, respectively. There were 13 device-related infections in 8 patients (57%) and 10 hypersensitivity reactions in 6 (43%).

CONCLUSIONS

Cerliponase alfa is well tolerated and has the potential to stabilize motor and language function in patients with atypical phenotypes of CLN2 disease.

Guidelines on the diagnosis, clinical assessments, treatment and management for CLN2 disease patients

Background

CLN2 disease (Neuronal Ceroid Lipofuscinosis Type 2) is an ultra-rare, neurodegenerative lysosomal storage disease, caused by an enzyme deficiency of tripeptidyl peptidase 1 (TPP1). Lack of disease awareness and the non-specificity of presenting symptoms often leads to delayed diagnosis. These guidelines provide robust evidence-based, expert-agreed recommendations on the risks/benefits of disease-modifying treatments and the medical interventions used to manage this condition.

Methods

An expert mapping tool process was developed ranking multidisciplinary professionals, with knowledge of CLN2 disease, diagnostic or management experience of CLN2 disease, or family support professionals. Individuals were sequentially approached to identify two chairs, ensuring that the process was transparent and unbiased. A systematic literature review of published evidence using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidance was independently and simultaneously conducted to develop key statements based upon the strength of the publications. Clinical care statements formed the basis of an international modified Delphi consensus determination process using the virtual meeting (Within3) online platform which requested experts to agree or disagree with any changes. Statements reaching the consensus mark became the guiding statements within this manuscript, which were subsequently assessed against the Appraisal of Guidelines for Research and Evaluation (AGREEII) criteria.

Results

Twenty-one international experts from 7 different specialities, including a patient advocate, were identified. Fifty-three guideline statements were developed covering 13 domains: General Description and Statements, Diagnostics, Clinical Recommendations and Management, Assessments, Interventions and Treatment, Additional Care Considerations, Social Care Considerations, Pain Management, Epilepsy / Seizures, Nutritional Care Interventions, Respiratory Health, Sleep and Rest, and End of Life Care. Consensus was reached after a single round of voting, with one exception which was revised, and agreed by 100% of the SC and achieved 80% consensus in the second voting round. The overall AGREE II assessment score obtained for the development of the guidelines was 5.7 (where 1 represents the lowest quality, and 7 represents the highest quality).

Conclusion

This program provides robust evidence- and consensus-driven guidelines that can be used by all healthcare professionals involved in the management of patients with CLN2 disease and other neurodegenerative disorders. This addresses the clinical need to complement other information available.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01813-5.

Gene Therapy for Lysosomal Storage Disorders: Ongoing Studies and Clinical Development

Rare monogenic disorders such as lysosomal diseases have been at the forefront in the development of novel treatments where therapeutic options are either limited or unavailable. The increasing number of successful pre-clinical and clinical studies in the last decade demonstrates that gene therapy represents a feasible option to address the unmet medical need of these patients. This article provides a comprehensive overview of the current state of the field, reviewing the most used viral gene delivery vectors in the context of lysosomal storage disorders, a selection of relevant pre-clinical studies and ongoing clinical trials within recent years.

Urine proteomics analysis of patients with neuronal ceroid lipofuscinoses

The neuronal ceroid lipofuscinoses (NCL) are a group of 13 rare neurodegenerative disorders characterized by accumulation of cellular storage bodies. There are few therapeutic options, and existing tests do not monitor disease progression and treatment response. However, urine biomarkers could address this need. Proteomic analysis of CLN2 patient urine revealed activation of immune response pathways and pathways associated with the unfolded protein response. Analysis of CLN5 and CLN6 sheep model urine showed subtle changes. To confirm and investigate the relevance of candidate biomarkers a targeted LC-MS/MS proteomic assay was created. We applied this assay to additional CLN2 samples as well as other patients with NCL (CLN1, CLN3, CLN5, CLN6, and CLN7) and demonstrated that hexosaminidase-A, aspartate aminotransferase-1, and LAMP1 are increased in NCL samples and betaine-homocysteine S-methyltransferase-1 was specifically increased in patients with CLN2. These proteins could be used to monitor the effectiveness of future therapies aimed at treating systemic NCL disease.

•

The urine proteome is altered in humans and animals with NCL

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Hexosaminidase A and LAMP1 are increased in patients with NCL

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Betaine-homocysteine S-methyltransferase 1 is elevated in CLN2 patients

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Proteins altered in CLN5 and CLN6 sheep models are not affected in humans

An In Vitro Whole-Organ Liver Engineering for Testing of Genetic Therapies

Explosion of gene therapy approaches for treating rare monogenic and common liver disorders created an urgent need for disease models able to replicate human liver cellular environment. Available models lack 3D liver structure or are unable to survive in long-term culture. We aimed to generate and test a 3D culture system that allows long-term maintenance of human liver cell characteristics. The in vitro whole-organ "Bioreactor grown Artificial Liver Model" (BALM) employs a custom-designed bioreactor for long-term 3D culture of human induced pluripotent stem cells-derived hepatocyte-like cells (hiHEPs) in a mouse decellularized liver scaffold. Adeno-associated viral (AAV) and lentiviral (LV) vectors were introduced by intravascular injection. Substantial AAV and LV transgene expression in the BALM-grown hiHEPs was detected. Measurement of secreted proteins in the media allowed non-invasive monitoring of the system. We demonstrated that humanized whole-organ BALM is a valuable tool to generate pre-clinical data for investigational medicinal products.

Clinical Pharmacokinetics and Pharmacodynamics of Cerliponase Alfa, Enzyme Replacement Therapy for CLN2 Disease by Intracerebroventricular Administration

Cerliponase alfa is recombinant human tripeptidyl peptidase 1 (TPP1) delivered by i.c.v. infusion for CLN2, a pediatric neurodegenerative disease caused by deficiency in lysosomal enzyme TPP1. We report the pharmacokinetics (PK) and pharmacodynamics of cerliponase alfa, the first i.c.v. enzyme replacement therapy, characterized in a phase I/II study. Escalating doses (30-300 mg Q2W) followed by 300 mg Q2W for ≥ 48 weeks were administered in 24 patients aged ≥ 3 years. Concentrations peaked in cerebrospinal fluid (CSF) at the end of ~ 4-hour i.c.v. infusion and 8 hours thereafter in plasma. Plasma exposure was 300-1,000-fold lower than in CSF, with no correlation in the magnitude of peak concentration (C_max ) or area under the concentration-time curve (AUC) among body sites. There was no apparent accumulation in CSF or plasma exposure with Q2W dosing. Interpatient and intrapatient variability of AUC, respectively, were 31-49% and 24% in CSF vs. 59-103% and 80% in plasma. PK variability was not explained by baseline demographics, as sex, age, weight, and CLN2 disease severity score did not appear to impact CSF or plasma PK. No apparent correlation was noted between CSF or plasma PK and incidence of adverse events (pyrexia, hypersensitivity, seizure, and epilepsy) or presence of antidrug antibodies in CSF and serum. There was no relationship between magnitude of CSF exposure and efficacy (change in CLN2 score from baseline), indicating maximum benefit was obtained across the range of exposures with 300 mg Q2W. Data from this small trial of ultra-rare disease were leveraged to adequately profile cerliponase alfa and support 300 mg i.c.v. Q2W for CLN2 treatment.

Loss-of-Function Variants in HOPS Complex Genes VPS16 and VPS41 Cause Early Onset Dystonia Associated with Lysosomal Abnormalities

OBJECTIVES

The majority of people with suspected genetic dystonia remain undiagnosed after maximal investigation, implying that a number of causative genes have not yet been recognized. We aimed to investigate this paucity of diagnoses.

METHODS

We undertook weighted burden analysis of whole-exome sequencing (WES) data from 138 individuals with unresolved generalized dystonia of suspected genetic etiology, followed by additional case-finding from international databases, first for the gene implicated by the burden analysis (VPS16), and then for other functionally related genes. Electron microscopy was performed on patient-derived cells.

RESULTS

Analysis revealed a significant burden for VPS16 (Fisher's exact test p value, 6.9 × 10⁹ ). VPS16 encodes a subunit of the homotypic fusion and vacuole protein sorting (HOPS) complex, which plays a key role in autophagosome-lysosome fusion. A total of 18 individuals harboring heterozygous loss-of-function VPS16 variants, and one with a microdeletion, were identified. These individuals experienced early onset progressive dystonia with predominant cervical, bulbar, orofacial, and upper limb involvement. Some patients had a more complex phenotype with additional neuropsychiatric and/or developmental comorbidities. We also identified biallelic loss-of-function variants in VPS41, another HOPS-complex encoding gene, in an individual with infantile-onset generalized dystonia. Electron microscopy of patient-derived lymphocytes and fibroblasts from both patients with VPS16 and VPS41 showed vacuolar abnormalities suggestive of impaired lysosomal function.

INTERPRETATION

Our study strongly supports a role for HOPS complex dysfunction in the pathogenesis of dystonia, although variants in different subunits display different phenotypic and inheritance characteristics. ANN NEUROL 2020;88:867-877.