Enhancing Equitable Access to Rare Disease Diagnosis and Treatment around the World: A Review of Evidence, Policies, and Challenges.

This document provides a comprehensive summary of evidence on the current situation of rare diseases (RDs) globally and regionally, including conditions, practices, policies, and regulations, as well as the challenges and barriers faced by RD patients, their families, and caregivers. The document builds on a review of academic literature and policies and a process of validation and feedback by a group of seven experts from across the globe. Panelists were selected based on their academic merit, expertise, and knowledge regarding the RD environment. The document is divided into five main sections: (1) methodology and objective; (2) background and context; (3) overview of the current situation and key challenges related to RDs covering six dimensions: burden of disease, patient journey, social impact, disease management, RD-related policies, and research and development; (4) recommendations; and (5) conclusions. The recommendations are derived from the discussion undertaken by the experts on the findings of this review and provide a set of actionable solutions to the challenges and barriers to improving access to RD diagnosis and treatment around the world. The recommendations can support critical decision-making, guiding efforts by a broad range of RDs stakeholders, including governments, international organizations, manufacturers, researchers, and patient advocacy groups.

The past, present, and future of child growth monitoring: A review and primer for clinical genetics.

Child growth measurements are critical vital signs to track, with every individual child growth curve potentially revealing a story about a child's health and well-being. Simply put, every baby born requires basic building blocks to grow and thrive: proper nutrition, love and care, and medical health. To ensure that every child who is missing one of these vital aspects is identified, growth is traditionally measured at birth and each well-child visit. While the blue and pink growth curves appear omnipresent in pediatric clinics, it is surprising to realize that their use only became standard of care in 1977 when the National Center for Health Statistics (NCHS) adopted the growth curve as a clinical tool for health. Behind this practice lies a socioeconomically, culturally, and politically complex interplay of individuals and institutions around the world. In this review, we highlight the often forgotten past, current state of practice, and future potential of this powerful clinical tool: the growth reference chart, with a particular focus on clinical genetics practice. The goal of this article is to understand ongoing work in the field of anthropometry (the scientific study of human measurements) and its direct impact on modern pediatric and genetic patient care.

Association of citrulline concentration at birth with lower respiratory tract infection in infancy: Findings from a multi-site birth cohort study.

Assessing the association of the newborn metabolic state with severity of subsequent respiratory tract infection may provide important insights on infection pathogenesis. In this multi-site birth cohort study, we identified newborn metabolites associated with lower respiratory tract infection (LRTI) in the first year of life in a discovery cohort and assessed for replication in two independent cohorts. Increased citrulline concentration was associated with decreased odds of LRTI (discovery cohort: aOR 0.83 [95% CI 0.70-0.99], p = 0.04; replication cohorts: aOR 0.58 [95% CI 0.28-1.22], p = 0.15). While our findings require further replication and investigation of mechanisms of action, they identify a novel target for LRTI prevention and treatment.

Amino acid signature during sickle cell pain crisis shows significant alterations related to nitric oxide and energy metabolism.

Nitric oxide depletion secondary to arginase induced arginine deficiency has been shown to be important in the pathophysiology of vaso-occlusion in sickle cell pain crisis. Our objective of this study was to perform a comprehensive amino acid evaluation during sickle cell pain crisis. In a total of 58 subjects (29 in steady-state sickle cell disease and 29 with sickle cell pain crisis), the amino acids related to nitric oxide pathway was significantly decreased during sickle cell pain crisis compared to steady-state sickle cell disease: arginine (p = 0.001), citrulline (p = 0.012), and ornithine (p = 0.03). In addition, the amino acids related to energy metabolism was significantly decreased during a pain crisis: asparagine (p < 0.001), serine (p = 0.002), histidine (p = 0.017), alanine (p = 0.004), tyrosine (p = 0.012), methionine (p = 0.007), cystine (p = 0.016), isoleucine (p = 0.016) and lysine (p = 0.006). The amino acid related to oxidative stress were significantly higher during a sickle cell pain crisis (glutamic acid (p < 0.001). Furthermore, multivariate analysis with partial least squares-discriminant analysis (PLS-DA) showed that deficiencies of the amino acids arginine, asparagine, citrulline, methionine and alanine were the most important related to sickle cell pain crisis.

The Rare Disease Research Scholars Program: A training curriculum for clinical researchers with mixed methods evaluation study.

Rare disease clinician investigators are essential to ensure appropriate diagnosis, care, and treatment for the rapidly growing rare disease population. As these researchers are spread across many specialties, learning the unique skill set for rare disease research (RDR) can be a hurdle and may hinder progress in the field. The need for an RDR focused training program for investigators in many specialties and backgrounds was identified in a needs assessment of trainees in the NIH funded Rare Diseases Clinical Research Network. Based on this information, the Rare Disease Research Scholars Program (RDRSP) was developed. We describe the needs assessment, curriculum creation, scholar recruitment, and outcome evaluation based on four years of programmatic data (2015-2019). This one year-long RDRSP uses a blended approach that includes in-person, web-based, synchronous and asynchronous learning. We evaluated the RDRSP using quantitative and qualitative approaches. Quantitative measures included pre and post questionnaires about knowledge, self-efficacy, and intent to remain in RDR. Data were analyzed using descriptive statistics and a paired t-test. Qualitative semi-structured interviews explored the RDR scholars' perceptions of the RDRSP; thematic analysis examined the textual data. Quantitative pre- and post-measures were statistically significant in the following areas: 1) improved knowledge content in RDR, 2) enhanced self-efficacy in clinical research, and 3) intent to remain in the field of RDR. Qualitative data analysis found the program supported the development of the scholar's research skills as well as 'soft-skills'. By combining training of skills unique to RDR with the more general topics of leadership, mentorship and collaboration among participants in diverse specialties, we created a program that supports the development of the next generation of rare disease clinician investigators and serves as a model for training in other niche research areas.

Acylcarnitines and Genetic Variation in Fat Oxidation Genes in HIV-infected, Antiretroviral-treated Children With and Without Myopathy.

BACKGROUND: Mitochondrial toxicity resulting in myopathy and lactic acidosis has been described in antiretroviral (ARV)-exposed patients. We hypothesized that myopathy in HIV-infected, ARV-treated children would be associated with metabolic (acylcarnitines) and genetic (variants in metabolic genes) markers of dysfunctional fatty acid oxidation (FAO). METHODS: Acylcarnitine profiles (ACP) were analyzed for 74 HIV-infected children on nucleoside reverse transcriptase inhibitor (NRTI)-containing ARV. Thirty-seven participants with ≥2 creatine kinase measurements >500 IU (n = 18) or evidence of echocardiographic cardiomyopathy (n = 19) were matched with 37 participants without myopathy. Single nucleotide polymorphisms (SNPs) in FAO genes were also evaluated. RESULTS: Abnormal ACP was 73% (95% CI: 56%-86%) and 62% (95% CI: 45%-78%) in the myopathic and nonmyopathic groups, respectively. No significant association was found between myopathy and having an abnormal ACP (OR = 2.10, P = 0.22). In univariate analysis, a 1-year increase in NRTI use was associated with a 20% increase in odds of at least 1 ACP abnormality [OR (95% CI) = 1.20 (1.03-1.41); P = 0.02), and a 1-year increase in protease inhibitor use was associated with 28% increase in the odds of having at least 1 ACP abnormality [OR (95% CI) = 1.28 (1.07-1.52); P = 0.006). Three SNPs, all in the gene for the carnitine transporter ( SLC22A5 ), were associated with the cardiomyopathy phenotype. CONCLUSION: FAO appears to be altered in HIV-infected children with and without myopathy, but abnormal FAO does not fully explain myopathy in ARV-exposed children. Further study of SLC22A5 variation in ARV-exposed people is warranted carnitine transporter dysfunction-related cardiomyopathy may be treatable.

Folic acid, either solely or combined with L-citrulline, improves NO signaling and ameliorates chronic hypoxia-induced pulmonary hypertension in newborn pigs.

Concomitant with developing pulmonary hypertension (PH), newborn piglets exposed to chronic hypoxia develop pulmonary vascular NO signaling impairments. PH is reduced and NO signaling is improved in chronically hypoxic piglets treated with the NO-arginine precursor, L-citrulline. Folic acid positively impacts NO signaling. We evaluated whether the effect on NO signaling and PH is greater using co-treatment with folic acid and L-citrulline than either alone. From day 3 to day 10 of hypoxia, piglets were treated solely with folic acid, solely with L-citrulline, or co-treated with both. Catheters were placed to measure in vivo hemodynamics. NO production was measured in vitro in dissected pulmonary arteries. Compared to normoxic piglets, pulmonary vascular resistance (PVR) was elevated and NO production was reduced in untreated hypoxic piglets. Regardless of treatment strategy, PVR was less in all three treated groups of hypoxic piglets when compared to the untreated hypoxic group. In addition, for all three groups of treated hypoxic piglets, NO production was higher than the untreated group. Improvements in PVR and NO production did not differ between piglets co-treated with folic acid and L-citrulline and those treated solely with either. Thus, the impact on NO production and PVR was not augmented by combining folic acid and L-citrulline treatments. Nonetheless, treatment with folic acid, either singly or when combined with L-citrulline, increases NO production and inhibits PH in chronically hypoxic newborn piglets. Folic acid merits consideration as a therapy for PH in human infants with chronic heart and lung conditions that are associated with chronic hypoxia.

Development and evaluation of a machine learning-based point-of-care screening tool for genetic syndromes in children: a multinational retrospective study.

BACKGROUND: Delays in the diagnosis of genetic syndromes are common, particularly in low and middle-income countries with limited access to genetic screening services. We, therefore, aimed to develop and evaluate a machine learning-based screening technology using facial photographs to evaluate a child's risk of presenting with a genetic syndrome for use at the point of care. METHODS: In this retrospective study, we developed a facial deep phenotyping technology based on deep neural networks and facial statistical shape models to screen children for genetic syndromes. We trained the machine learning models on facial photographs from children (aged <21 years) with a clinical or molecular diagnosis of a genetic syndrome and controls without a genetic syndrome matched for age, sex, and race or ethnicity. Images were obtained from three publicly available databases (the Atlas of Human Malformations in Diverse Populations of the National Human Genome Research Institute, Face2Gene, and the dataset available from Ferry and colleagues) and the archives of the Children's National Hospital (Washington, DC, USA), in addition to photographs taken on a standard smartphone at the Children's National Hospital. We designed a deep learning architecture structured into three neural networks, which performed image standardisation (Network A), facial morphology detection (Network B), and genetic syndrome risk estimation, accounting for phenotypic variations due to age, sex, and race or ethnicity (Network C). Data were divided randomly into 40 groups for cross validation, and the performance of the model was evaluated in terms of accuracy, sensitivity, and specificity in both the total population and stratified by race or ethnicity, age, and sex. FINDINGS: Our dataset included 2800 facial photographs of children (1318 [47%] female and 1482 [53%] male; 1576 [56%] White, 432 [15%] African, 430 [15%] Hispanic, and 362 [13%] Asian). 1400 children with 128 genetic conditions were included (the most prevalent being Williams-Beuren syndrome [19%], Cornelia de Lange syndrome [17%], Down syndrome [16%], 22q11.2 deletion [13%], and Noonan syndrome [12%] syndrome) in addition to 1400 photographs of matched controls. In the total population, our deep learning-based model had an accuracy of 88% (95% CI 87-89) for the detection of a genetic syndrome, with 90% sensitivity (95% CI 88-92) and 86% specificity (95% CI 84-88). Accuracy was greater in White (90%, 89-91) and Hispanic populations (91%, 88-94) than in African (84%, 81-87) and Asian populations (82%, 78-86). Accuracy was also similar in male (89%, 87-91) and female children (87%, 85-89), and similar in children younger than 2 years (86%, 84-88) and children aged 2 years or older (eg, 89% [87-91] for those aged 2 years to <5 years). INTERPRETATION: This genetic screening technology could support early risk stratification at the point of care in global populations, which has the potential accelerate diagnosis and reduce mortality and morbidity through preventive care. FUNDING: Children's National Hospital and Government of Abu Dhabi.

A novel small molecule approach for the treatment of propionic and methylmalonic acidemias.

Propionic Acidemia (PA) and Methylmalonic Acidemia (MMA) are inborn errors of metabolism affecting the catabolism of valine, isoleucine, methionine, threonine and odd-chain fatty acids. These are multi-organ disorders caused by the enzymatic deficiency of propionyl-CoA carboxylase (PCC) or methylmalonyl-CoA mutase (MUT), resulting in the accumulation of propionyl-coenzyme A (P-CoA) and methylmalonyl-CoA (M-CoA in MMA only). Primary metabolites of these CoA esters include 2-methylcitric acid (MCA), propionyl-carnitine (C3), and 3-hydroxypropionic acid, which are detectable in both PA and MMA, and methylmalonic acid, which is detectable in MMA patients only (Chapman et al., 2012). We deployed liver cell-based models that utilized PA and MMA patient-derived primary hepatocytes to validate a small molecule therapy for PA and MMA patients. The small molecule, HST5040, resulted in a dose-dependent reduction in the levels of P-CoA, M-CoA (in MMA) and the disease-relevant biomarkers C3, MCA, and methylmalonic acid (in MMA). A putative working model of how HST5040 reduces the P-CoA and its derived metabolites involves the conversion of HST5040 to HST5040-CoA driving the redistribution of free and conjugated CoA pools, resulting in the differential reduction of the aberrantly high P-CoA and M-CoA. The reduction of P-CoA and M-CoA, either by slowing production (due to increased demands on the free CoA (CoASH) pool) or enhancing clearance (to replenish the CoASH pool), results in a net decrease in the CoA-derived metabolites (C3, MCA and MMA (MMA only)). A Phase 2 study in PA and MMA patients will be initiated in the United States.

Rapid deployment of a telemedicine care model for genetics and metabolism during COVID-19.

The national importance of telemedicine for safe and effective patient care has been highlighted by the current COVID-19 pandemic. Prior to the 2020 pandemic the Division of Genetics and Metabolism piloted a telemedicine program focused on initial and follow-up visits in the patients' home. The goals were to increase access to care, decrease missed work, improve scheduling, and avoid the transport and exposure of medically fragile patients. Visits were conducted by physician medical geneticists, genetic counselors, and biochemical dietitians, together and separately. This allowed the program to develop detailed standard operating procedures. At the onset of the COVID-19 pandemic, this pilot-program was deployed by the full team of 22 providers in one business day. Two physicians remained on-site for patients requiring in-person evaluations. This model optimized patient safety and workforce preservation while providing full access to patients during a pandemic. We provide initial data on visit numbers, types of diagnoses, and no-show rates. Experience in this implementation before and during the pandemic has confirmed the effectiveness and value of telemedicine for a highly complex medical population. This program is a model that can and will be continued well-beyond the current crisis.

Biochemical and anaplerotic applications of in vitro models of propionic acidemia and methylmalonic acidemia using patient-derived primary hepatocytes.

Propionic acidemia (PA) and methylmalonic acidemia (MMA) are autosomal recessive disorders of propionyl-CoA (P-CoA) catabolism, which are caused by a deficiency in the enzyme propionyl-CoA carboxylase or the enzyme methylmalonyl-CoA (MM-CoA) mutase, respectively. The functional consequence of PA or MMA is the inability to catabolize P-CoA to MM-CoA or MM-CoA to succinyl-CoA, resulting in the accumulation of P-CoA and other metabolic intermediates, such as propionylcarnitine (C3), 3-hydroxypropionic acid, methylcitric acid (MCA), and methylmalonic acid (only in MMA). P-CoA and its metabolic intermediates, at high concentrations found in PA and MMA, inhibit enzymes in the first steps of the urea cycle as well as enzymes in the tricarboxylic acid (TCA) cycle, causing a reduction in mitochondrial energy production. We previously showed that metabolic defects of PA could be recapitulated using PA patient-derived primary hepatocytes in a novel organotypic system. Here, we sought to investigate whether treatment of normal human primary hepatocytes with propionate would recapitulate some of the biochemical features of PA and MMA in the same platform. We found that high levels of propionate resulted in high levels of intracellular P-CoA in normal hepatocytes. Analysis of TCA cycle intermediates by GC-MS/MS indicated that propionate may inhibit enzymes of the TCA cycle as shown in PA, but is also incorporated in the TCA cycle, which does not occur in PA. To better recapitulate the disease phenotype, we obtained hepatocytes derived from livers of PA and MMA patients. We characterized the PA and MMA donors by measuring key proximal biomarkers, including P-CoA, MM-CoA, as well as clinical biomarkers propionylcarnitine-to-acetylcarnitine ratios (C3/C2), MCA, and methylmalonic acid. Additionally, we used isotopically-labeled amino acids to investigate the contribution of relevant amino acids to production of P-CoA in models of metabolic stability or acute metabolic crisis. As observed clinically, we demonstrated that the isoleucine and valine catabolism pathways are the greatest sources of P-CoA in PA and MMA donor cells and that each donor showed differential sensitivity to isoleucine and valine. We also studied the effects of disodium citrate, an anaplerotic therapy, which resulted in a significant increase in the absolute concentration of TCA cycle intermediates, which is in agreement with the benefit observed clinically. Our human cell-based PA and MMA disease models can inform preclinical drug discovery and development where mouse models of these diseases are inaccurate, particularly in well-described species differences in branched-chain amino acid catabolism.

Combined l-citrulline and tetrahydrobiopterin therapy improves NO signaling and ameliorates chronic hypoxia-induced pulmonary hypertension in newborn pigs.

Newborn pigs with chronic hypoxia-induced pulmonary hypertension (PH) have evidence of endothelial nitric oxide synthase (eNOS) uncoupling. In this model, we showed that therapies that promote eNOS coupling, either tetrahydrobiopterin (BH4), a NOS cofactor, or l-citrulline, a NO-l-arginine precursor, inhibit PH. We wanted to determine whether cotreatment with l-citrulline and a BH4 compound, sapropterin dihydrochloride, improves NO signaling and chronic hypoxia-induced PH more markedly than either alone. Normoxic (control) and hypoxic piglets were studied. Some hypoxic piglets received sole treatment with l-citrulline or BH4, or were cotreated with l-citrulline and BH4, from day 3 through day 10 of hypoxia. Catheters were placed for hemodynamic measurements, and pulmonary arteries were dissected to assess eNOS dimer-to-monomer ratios and NO production. In untreated hypoxic piglets, pulmonary vascular resistance (PVR) was higher and NO production and eNOS dimer-to-monomer ratios were lower than in normoxic piglets. Compared with the untreated hypoxic group, PVR was lower in hypoxic piglets cotreated with l-citrulline and BH4 and in those treated with l-citrulline alone but not for those treated solely with BH4. NO production and eNOS dimer-to-monomer ratios were greater for all three treated hypoxic groups compared with the untreated group. Notably, greater improvements in PVR, eNOS dimer-to-monomer ratios, and NO production were found in hypoxic piglets cotreated with l-citrulline and BH4 than in piglets treated with either alone. Cotreatment with l-citrulline and BH4 more effectively improves NO signaling and inhibits chronic hypoxia-induced PH than either treatment alone. Combination therapies may offer enhanced therapeutic capacity for challenging clinical conditions, such as chronic neonatal PH.

Tricarboxylic acid cycle enzyme activities in a mouse model of methylmalonic aciduria.

Methylmalonic acidemia (MMA) is a propionate pathway disorder caused by dysfunction of the mitochondrial enzyme methylmalonyl-CoA mutase (MMUT). MMUT catalyzes the conversion of methylmalonyl-CoA to succinyl-CoA, an anaplerotic reaction which feeds into the tricarboxylic acid (TCA) cycle. As part of the pathological mechanisms of MMA, previous studies have suggested there is decreased TCA activity due to a "toxic inhibition" of TCA cycle enzymes by MMA related metabolites, in addition to reduced anaplerosis. Here, we have utilized mitochondria isolated from livers of a mouse model of MMA (Mut-ko/ki) and their littermate controls (Ki/wt) to examine the amounts and enzyme functions of most of the TCA cycle enzymes. We have performed mRNA quantification, protein semi-quantitation, and enzyme activity quantification for TCA cycle enzymes in these samples. Expression profiling showed increased mRNA levels of fumarate hydratase in the Mut-ko/ki samples, which by contrast had reduced protein levels as detected by immunoblot, while all other mRNA levels were unaltered. Immunoblotting also revealed decreased protein levels of 2-oxoglutarate dehydrogenase and malate dehydrogenase 2. Interesting, the decreased protein amount of 2-oxoglutarate dehydrogenase was reflected in decreased activity for this enzyme while there is a trend towards decreased activity of fumarate hydratase and malate dehydrogenase 2. Citrate synthase, isocitrate dehydrogenase 2/3, succinyl-CoA synthase, and succinate dehydrogenase are not statistically different in terms of quantity of enzyme or activity. Finally, we found decreased activity when examining the function of methylmalonyl-CoA mutase in series with succinate synthase and succinate dehydrogenase in the Mut-ko/ki mice compared to their littermate controls, as expected. This study demonstrates decreased activity of certain TCA cycle enzymes and by corollary decreased TCA cycle function, but it supports decreased protein quantity rather than "toxic inhibition" as the underlying mechanism of action. SUMMARY: Methylmalonic acidemia (MMA) is an inborn metabolic disorder of propionate catabolism. In this disorder, toxic metabolites are considered to be the major pathogenic mechanism for acute and long-term complications. However, despite optimized therapies aimed at reducing metabolite levels, patients continue to suffer from late complications, including metabolic stroke and renal insufficiency. Since the propionate pathway feeds into the tricarboxylic acid (TCA) cycle, we investigated TCA cycle function in a constitutive MMA mouse model. We demonstrated decreased amounts of the TCA enzymes, Mdh2 and Ogdh as semi-quantified by immunoblot. Enzymatic activity of Ogdh is also decreased in the MMA mouse model compared to controls. Thus, when the enzyme amounts are decreased, we see the enzymatic activity also decreased to a similar extent for Ogdh. Further studies to elucidate the structural and/or functional links between the TCA cycle and propionate pathways might lead to new treatment approaches for MMA patients.

Decreased plasma l-arginine levels in organic acidurias (MMA and PA) and decreased plasma branched-chain amino acid levels in urea cycle disorders as a potential cause of growth retardation: Options for treatment.

BACKGROUND AND AIM: Patients with methylmalonic acidemia (MMA) and propionic acidemia (PA) and urea cycle disorders (UCD), treated with a protein restricted diet, are prone to growth failure. To obtain optimal growth and thereby efficacious protein incorporation, a diet containing the essential and functional amino acids for growth is necessary. Optimal growth will result in improved protein tolerance and possibly a decrease in the number of decompensations. It thus needs to be determined if amino acid deficiencies are associated with the growth retardation in these patient groups. We studied the correlations between plasma L-arginine levels, plasma branched chain amino acids (BCAA: L-isoleucine, L-leucine and L-valine) levels (amino acids known to influence growth), and height in MMA/PA and UCD patients. METHODS: We analyzed data from longitudinal visits made in stable metabolic periods by patients registered at the European Registry and Network for Intoxication Type Metabolic Diseases (E-IMD, Chafea no. 2010 12 01). RESULTS: In total, 263 MMA/PA and 311 UCD patients were included, all aged below 18 years of age. In patients with MMA and PA, height z-score was positively associated with patients' natural-protein-to-energy prescription ratio and their plasma L-valine and L-arginine levels, while negatively associated with the amount of synthetic protein prescription and their age at visit. In all UCDs combined, height z-score was positively associated with the natural-protein-to-energy prescription ratio. In those with carbamylphosphate synthetase 1 deficiency (CPS1-D), those with male ornithine transcarbamylase deficiency (OTC-D), and those in the hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome subgroup, height z-score was positively associated with patients' plasma L-leucine levels. In those with argininosuccinate synthetase deficiency (ASS-D) and argininosuccinate lyase deficiency (ASL-D), height was positively associated with patients' plasma L-valine levels. CONCLUSION: Plasma L-arginine and L-valine levels in MMA/PA patients and plasma L-leucine and L-valine levels in UCD patients, as well as the protein-to-energy prescription ratio in both groups were positively associated with height. Optimization of these plasma amino acid levels is essential to support normal growth and increase protein tolerance in these disorders. Consequently this could improve the protein-to-energy intake ratio.

Evaluation of dietary treatment and amino acid supplementation in organic acidurias and urea-cycle disorders: On the basis of information from a European multicenter registry.

Organic acidurias (OAD) and urea-cycle disorders (UCD) are rare inherited disorders affecting amino acid and protein metabolism. As dietary practice varies widely, we assessed their long-term prescribed dietary treatment against published guideline and studied plasma amino acids levels. We analyzed data from the first visit recorded in the European registry and network for intoxication type metabolic diseases (E-IMD, Chafea no. 2010 12 01). In total, 271 methylmalonic aciduria (MMA) and propionic aciduria (PA) and 361 UCD patients were included. Median natural protein prescription was consistent with the recommended daily allowance (RDA), plasma L-valine (57%), and L-isoleucine (55%) levels in MMA and PA lay below reference ranges. Plasma levels were particularly low in patients who received amino acid mixtures (AAMs-OAD) and L-isoleucine:L-leucine:L-valine (BCAA) ratio was 1.0:3.0:3.2. In UCD patients, plasma L-valine, L-isoleucine, and L-leucine levels lay below reference ranges in 18%, 30%, and 31%, respectively. In symptomatic UCD patients who received AAM-UCD, the median natural protein prescription lay below RDA, while their L-valine and L-isoleucine levels and plasma BCAA ratios were comparable to those in patients who did not receive AAM-UCD. Notably, in patients with ornithine transcarbamylase syndrome (OTC-D), carbamylphosphate synthetase 1 syndrome (CPS1-D) and hyperammonemia-hyperornithinemia-homocitrullinemia (HHH) syndrome selective L-citrulline supplementation resulted in higher plasma L-arginine levels than selective L-arginine supplementation. In conclusion, while MMA and PA patients who received AAMs-OAD had very low BCAA levels and disturbed plasma BCAA ratios, AAMs-UCD seemed to help UCD patients obtain normal BCAA levels. In patients with OTC-D, CPS1-D, and HHH syndrome, selective L-citrulline seemed preferable to selective L-arginine supplementation.

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.