On the Creation, Utility and Sustaining of Rare Diseases Research Networks: Lessons learned from the Urea Cycle Disorders Consortium, the Japanese Urea Cycle Disorders Consortium and the European Registry and Network for Intoxication Type Metabolic Diseases

Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders

OBJECTIVE

Liver transplantation (LTx) is an intervention when medical management is not sufficiently preventing individuals with urea cycle disorders (UCDs) from the occurrence of hyperammonemic events. Supplementation with L-citrulline/arginine is regularly performed prior to LTx to support ureagenesis and is often continued after the intervention. However, systematic studies assessing the impact of long-term L-citrulline/arginine supplementation in individuals who have undergone LTx is lacking to date.

METHODS

Using longitudinal data collected systematically, a comparative analysis was carried out by studying the effects of long-term L-citrulline/arginine supplementation vs. no supplementation on health-related outcome parameters (i.e., anthropometric, neurological, and cognitive outcomes) in individuals with UCDs who have undergone LTx. Altogether, 52 individuals with male ornithine transcarbamylase deficiency, citrullinemia type 1 and argininosuccinic aciduria and a pre-transplant "severe" disease course who have undergone LTx were investigated by using recently established and validated genotype-specific in vitro enzyme activities.

RESULTS

Long-term supplementation of individuals with L-citrulline/arginine who have undergone LTx (n = 16) does neither appear to alter anthropometric nor neurocognitive endpoints when compared to their severity-adjusted counterparts that were not supplemented (n = 36) after LTx with mean observation periods between four to five years. Moreover, supplementation with L-citrulline/arginine was not associated with an increase of disease-specific plasma arithmetic mean values for the respective amino acids when compared to the non-supplemented control cohort.

CONCLUSION

Although supplementation with L-citrulline/arginine is often continued after LTx, this pilot study does neither identify altered long-term anthropometric or neurocognitive health-related outcomes nor does it find an adequate biochemical response as reflected by the unaltered plasma arithmetic mean values for L-citrulline or L-arginine. Further prospective analyses in larger samples and even longer observation periods will provide more insight into the usefulness of long-term supplementation with L-citrulline/arginine for individuals with UCDs who have undergone LTx.

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.

Natural history of arginase 1 deficiency and the unmet needs of patients: A systematic review of case reports

Background

Arginase 1 deficiency (ARG1‐D) is a rare, progressive and debilitating urea cycle disorder characterized by clinical manifestations including spasticity, seizures, developmental delay, and intellectual disability. The aim of this systematic review was to identify and summarize the natural history of ARG1‐D and the unmet needs of patients.

Methods

A comprehensive search of published case reports was undertaken to identify patients with ARG1‐D regardless of interventions, comparisons, or outcomes. MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and other evidence‐based medicine literature databases were searched on 20 April 2020. Quality was assessed using the Joanna Briggs Institute (JBI) Critical Appraisal Checklist. (PROSPERO registration: CRD42020212142.)

Results

One hundred and fifty seven ARG1‐D patients were included from 111 publications (good overall quality based on JBI's Checklist); 84 (53.5%) were males. Motor deficits (including spasticity), intellectual disability, and seizures were reported in >50% of the cases. Mean age (SD) at diagnosis was 6.4 years and the laboratory findings most commonly reported to support diagnosis included elevated plasma arginine (81.5%), mutation in ARG1 gene through genetic testing (60%), and absence/reduction of red blood cell arginase activity (51%). Reported management approaches mainly included dietary protein restriction (68%), nitrogen scavengers (45%), and essential amino acid supplements (21%). Author‐reported clinical improvement was documented for 26% of patients, 15% deteriorated, and 19% had limited or no change; notably, no indication of clinical outcome was reported for 40% cases.

Conclusion

This review illustrates a significant burden of disease and highlights a considerable unmet need for clinically effective treatment options for patients with ARG1‐D.

Developments in evidence creation for treatments of inborn errors of metabolism

Inborn errors of metabolism (IEM) represent the first group of genetic disorders, amenable to causal therapies. In addition to traditional medical diet and cofactor treatments, new treatment strategies such as enzyme replacement and small molecule therapies, solid organ transplantation, and cell-and gene-based therapies have become available. Inherent to the rare nature of the single conditions, generating high-quality evidence for these treatments in clinical trials and under real-world conditions has been challenging. Guidelines developed with standardized methodologies have contributed to improve the practice of care and long-term clinical outcomes. Adaptive trial designs allow for changes in sample size, group allocation and trial duration as the trial proceeds. n-of-1 studies may be used in small sample sized when participants are clinically heterogeneous. Multicenter observational and registry-based clinical trials are promoted via international research networks. Core outcome and standard data element sets will enhance comparative analysis of clinical trials and observational studies. Patient-centered outcome-research as well as patient-led research initiatives will further accelerate the development of therapies for IEM.

Factors Influencing the Generation of Evidence from Simple Data Held in International Rare Disease Patient Registries

BACKGROUND

Rare diseases (defined as affecting < 1 in 2000 Europeans) may collectively affect up to approximately 8% of the population. The low prevalence of individual diseases limits patient studies and data collection is a key challenge; international rare disease patient registries are essential for optimal data collection and research. Registry data achieves value when research conducted on them are published-this is termed evidence generation.

OBJECTIVE

The aim of this study was to examine selected factors and their association with evidence generation, via scientific publication, from international rare disease patient registry data.

METHODS

All international rare disease patient registries listed in the Orphanet 2018 report were analysed. Rates of scientific publications were compared by funding stream, disease area and registry size using multivariable regression analyses. Publication characteristics, such as novelty of findings, were also compared by registry funding stream, disease area and duration of operation.

RESULTS

Privately funded registries had approximately two to four times higher rates of scientific publication compared with publically funded registries, with adjusted rate ratios of 1.85 (95% confidence interval [CI] 1.07-3.22) and 4.18 (95% CI 2.54-6.87) for private not-for-profit and private for-profit funding, respectively. The inclusion of outcomes, use of pharmaceutical medicines, novel findings and citation rate for publications generated from patient registries with any private funding was not significantly different from those attributed to only publicly funded registries.

CONCLUSION

The results of this study indicate that privately funded international rare disease patient registries produce significantly more evidence than their publicly funded counterparts. Examination of the quality indicators of these publications showed they were of the same high quality as those generated from publicly funded patient registry data.

Impact of Diagnosis and Therapy on Cognitive Function in Urea Cycle Disorders

OBJECTIVE

Individuals with urea cycle disorders (UCDs) often present with intellectual and developmental disabilities. The major aim of this study was to evaluate the impact of diagnostic and therapeutic interventions on cognitive outcomes in UCDs.

METHODS

This prospective, observational, multicenter study includes data from 503 individuals with UCDs who had comprehensive neurocognitive testing with a cumulative follow-up of 702 patient-years.

RESULTS

The mean cognitive standard deviation score (cSDS) was lower in symptomatic than in asymptomatic (p < 0.001, t test) individuals with UCDs. Intellectual disability (intellectual quotient < 70, cSDS < -2.0) was associated with the respective subtype of UCD and early disease onset, whereas height of the initial peak plasma ammonium concentration was inversely associated with neurocognitive outcomes in mitochondrial (proximal) rather than cytosolic (distal) UCDs. In ornithine transcarbamylase and argininosuccinate synthetase 1 deficiencies, we did not find evidence that monoscavenger therapy with sodium or glycerol phenylbutyrate was superior to sodium benzoate in providing cognitive protection. Early liver transplantation appears to be beneficial for UCDs. It is noteworthy that individuals with argininosuccinate synthetase 1 and argininosuccinate lyase deficiencies identified by newborn screening had better neurocognitive outcomes than those diagnosed after the manifestation of first symptoms.

INTERPRETATION

Cognitive function is related to interventional and non-interventional variables. Early detection by newborn screening and early liver transplantation appear to offer greater cognitive protection, but none of the currently used nitrogen scavengers was superior with regard to long-term neurocognitive outcome. Further confirmation could determine these variables as important clinical indicators of neuroprotection for individuals with UCDs. ANN NEUROL 2019.

Transatlantic combined and comparative data analysis of 1095 patients with urea cycle disorders-A successful strategy for clinical research of rare diseases

BACKGROUND

To improve our understanding of urea cycle disorders (UCDs) prospectively followed by two North American (NA) and European (EU) patient cohorts.

AIMS

Description of the NA and EU patient samples and investigation of the prospects of combined and comparative analyses for individuals with UCDs.

METHODS

Retrieval and comparison of the data from 1095 individuals (NA: 620, EU: 475) from two electronic databases.

RESULTS

The proportion of females with ornithine transcarbamylase deficiency (fOTC-D), particularly those being asymptomatic (asfOTC-D), was higher in the NA than in the EU sample. Exclusion of asfOTC-D resulted in similar distributions in both samples. The mean age at first symptoms was higher in NA than in EU patients with late onset (LO), but similar for those with early (≤ 28 days) onset (EO) of symptoms. Also, the mean age at diagnosis and diagnostic delay for EO and LO patients were similar in the NA and EU cohorts. In most patients (including fOTC-D), diagnosis was made after the onset of symptoms (59.9%) or by high-risk family screening (24.7%), and less often by newborn screening (8.9%) and prenatal testing (3.7%). Analysis of clinical phenotypes revealed that EO patients presented with more symptoms than LO individuals, but that numbers of symptoms correlated with plasma ammonium concentrations in EO patients only. Liver transplantation was reported for 90 NA and 25 EU patients.

CONCLUSIONS

Combined analysis of databases drawn from distinct populations opens the possibility to increase sample sizes for natural history questions, while comparative analysis utilizing differences in approach to treatment can evaluate therapeutic options and enhance long-term outcome studies.

Cohort study of neurocognitive functioning and adaptive behaviour in children and adolescents with Niemann-Pick Disease type C1

AIM

To describe the neurocognitive and adaptive behavior profile of children and adolescents with Niemann-Pick Disease type C1 (NPC1), a rare genetic disease that frequently presents in childhood, with variable onset and symptom complex involving neurodegeneration.

METHOD

Thirty-eight participants (20 males, 18 females; mean age 8y 10mo, SD 4y 8mo, range 1-18y) with NPC1 were evaluated through a natural history protocol.

RESULTS

NPC1 severity was in the mild to moderate range for most participants. Cognitive scores (n=32) ranged from very low to above average; about half of the participants exhibited a clinically significant advantage of Verbal IQ over Non-verbal IQ. Adaptive behavior scores (n=21) were generally in the borderline to impaired range. Longitudinal cognitive data (n=19) suggested a pattern of decreasing scores over time. However, most participants remained at the same general level of functioning throughout the study.

INTERPRETATION

This study begins to systematically describe the neurocognitive phenotype of children and adolescents with NPC1, identifying heterogeneity and decline, aiding in understanding the natural history of the disease to plan treatment studies.

Pediatric registries at the Food and Drug Administration: design aspects that increase their likelihood of success

PURPOSE

To determine aspects of the design of pediatric registries that contribute to the success of registries conducted as a postmarketing study following approval of drugs or biological products by the US Food and Drug Administration.

METHODS

Pediatric registries for drugs and biological products were identified by searching the US Food and Drug Administration Postmarketing Requirements and Commitments database. Based on the recruitment of patients, the meeting of predetermined deadlines, and the submission of data, we classified studies as successful, unsuccessful, or unevaluable. Design aspects of successful and unsuccessful registries were examined for commonalities.

RESULTS

Thirty-eight studies were identified, and ten registries met the criteria for successful. Four (40%) successful registries utilized a registry established prior to product approval, and six (60%) were disease-based. Among unsuccessful registries, none were disease-based or utilized a pre-existing registry.

CONCLUSIONS

Characteristics identified as more common to successful registries included utilizing a disease-based registry and a registry established prior to product approval. Future studies might examine a larger sample of registries to see if these aspects consistently result in successful studies. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Genotype-Phenotype Correlations in Ornithine Transcarbamylase Deficiency: A Mutation Update

Ornithine transcarbamylase (OTC) deficiency is an X-linked trait that accounts for nearly half of all inherited disorders of the urea cycle. OTC is one of the enzymes common to both the urea cycle and the bacterial arginine biosynthesis pathway; however, the role of OTC has changed over evolution. For animals with a urea cycle, defects in OTC can trigger hyperammonemic episodes that can lead to brain damage and death. This is the fifth mutation update for human OTC with previous updates reported in 1993, 1995, 2002, and 2006. In the 2006 update, 341 mutations were reported. This current update contains 417 disease-causing mutations, and also is the first report of this series to incorporate information about natural variation of the OTC gene in the general population through examination of publicly available genomic data and examination of phenotype/genotype correlations from patients participating in the Urea Cycle Disorders Consortium Longitudinal Study and the first to evaluate the suitability of systematic computational approaches to predict severity of disease associated with different types of OTC mutations.