New variants expand the neurological phenotype of COQ7 deficiency.

The protein encoded by COQ7 is required for CoQ10 synthesis in humans, hydroxylating 3-demethoxyubiquinol (DMQ10) in the second to last steps of the pathway. COQ7 mutations lead to a primary CoQ10 deficiency syndrome associated with a pleiotropic neurological disorder. This study shows the clinical, physiological, and molecular characterization of four new cases of CoQ10 primary deficiency caused by five mutations in COQ7, three of which have not yet been described, inducing mitochondrial dysfunction in all patients. However, the specific combination of the identified variants in each patient generated precise pathophysiological and molecular alterations in fibroblasts, which would explain the differential in vitro response to supplementation therapy. Our results suggest that COQ7 dysfunction could be caused by specific structural changes that affect the interaction with COQ9 required for the DMQ10 presentation to COQ7, the substrate access to the active site, and the maintenance of the active site structure. Remarkably, patients' fibroblasts share transcriptional remodeling, supporting a modification of energy metabolism towards glycolysis, which could be an adaptive mechanism against CoQ10 deficiency. However, transcriptional analysis of mitochondria-associated pathways showed distinct and dramatic differences between patient fibroblasts, which correlated with the extent of pathophysiological and neurological alterations observed in the probands. Overall, this study suggests that the combination of precise genetic diagnostics and the availability of new structural models of human proteins could help explain the origin of phenotypic pleiotropy observed in some genetic diseases and the different responses to available therapies.

Carglumic acid in methylmalonic acidemia: Use of breast milk as an alternative vehicle to water.

WHAT IS KNOWN AND OBJECTIVE: Carbaglu® or N-carbamylglutamate (NCG) is not recommended for administration in a vehicle other than water. We aim to report the use of breast milk (BM) as an alternative vehicle in a neonate rejecting NCG diluted in water. CASE SUMMARY: A neonate diagnosed with methylmalonic acidemia presented symptomatology of acidemia and hyperammonemia. After the patient refused oral NCG administration, a dissolution test was conducted in BM showing correct dissolution. The NCG-BM solution was tolerated and plasma ammonium concentrations remained within range in subsequent analytical controls. WHAT IS NEW AND CONCLUSION: BM as a vehicle for NCG is a safe and effective option for patients who refuse suspension in water and could lead to better treatment compliance in paediatric patients.

A multicenter open-label extension study of intrathecal heparan-N-sulfatase in patients with Sanfilippo syndrome type A.

Sanfilippo syndrome type A (mucopolysaccharidosis type IIIA) is a rare autosomal recessive lysosomal disorder characterized by deficient heparan-N-sulfatase (HNS) activity, and subsequent accumulation of heparan sulfate, especially in the central nervous system. The disease is associated with progressive neurodegeneration in early childhood. For this open-label extension study of a phase 2b clinical trial, we report on safety and cognitive decline in patients receiving intrathecal (IT) administration of recombinant human HNS (rhHNS). Of 21 patients who completed the phase 2b study, 17 continued in the open-label extension. Patients receiving rhHNS IT 45 mg continued to receive the same treatment regimen (i.e., every 2 weeks or every 4 weeks) throughout the extension. Patients receiving no treatment in the phase 2b study were re-randomized to the treatment groups. Neurocognition was assessed using the Bayley Scales of Infant and Toddler Development®, Third Edition (BSID-III). Adverse events were recorded over the duration of the treatment period. Cognitive decline was observed in most patients in both treatment groups; however, improvements in BSID-III development quotient score were observed for two patients, in receptive and expressive communication scores for three patients each, in fine motor skills for one patient, and in gross motor skills for six patients. Treatment-emergent adverse events that occurred with rhHNS IT were mostly mild, none led to study discontinuation, and there were no deaths. The extension study was terminated early as the primary endpoints of the phase 2b study were not met, and no statistical analyses were carried out. Although cognitive decline was apparent in most patients, improvements were observed in a small group of patients. Greater declines were observed in patients at the higher end of the age range, suggesting earlier intervention may increase the possibility of a response to treatment. rhHNS IT treatment remained generally well tolerated up to 96 weeks.

Efficacy and safety of arimoclomol in Niemann-Pick disease type C: Results from a double-blind, randomised, placebo-controlled, multinational phase 2/3 trial of a novel treatment.

Niemann-Pick disease type C (NPC) is a rare, genetic, progressive neurodegenerative disorder with high unmet medical need. We investigated the safety and efficacy of arimoclomol, which amplifies the heat shock response to target NPC protein misfolding and improve lysosomal function, in patients with NPC. In a 12-month, prospective, randomised, double-blind, placebo-controlled, phase 2/3 trial (ClinicalTrials.gov identifier: NCT02612129), patients (2-18 years) were randomised 2:1 to arimoclomol:placebo, stratified by miglustat use. Routine clinical care was maintained. Arimoclomol was administered orally three times daily. The primary endpoint was change in 5-domain NPC Clinical Severity Scale (NPCCSS) score from baseline to 12 months. Fifty patients enrolled; 42 completed. At month 12, the mean progression from baseline in the 5-domain NPCCSS was 0.76 with arimoclomol vs 2.15 with placebo. A statistically significant treatment difference in favour of arimoclomol of -1.40 (95% confidence interval: -2.76, -0.03; P = .046) was observed, corresponding to a 65% reduction in annual disease progression. In the prespecified subgroup of patients receiving miglustat as routine care, arimoclomol resulted in stabilisation of disease severity over 12 months with a treatment difference of -2.06 in favour of arimoclomol (P = .006). Adverse events occurred in 30/34 patients (88.2%) receiving arimoclomol and 12/16 (75.0%) receiving placebo. Fewer patients had serious adverse events with arimoclomol (5/34, 14.7%) vs placebo (5/16, 31.3%). Treatment-related serious adverse events (n = 2) included urticaria and angioedema. Arimoclomol provided a significant and clinically meaningful treatment effect in NPC and was well tolerated.

Delineating the neurological phenotype in children with defects in the ECHS1 or HIBCH gene.

The neurological phenotype of 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) and short-chain enoyl-CoA hydratase (SCEH) defects is expanding and natural history studies are necessary to improve clinical management. From 42 patients with Leigh syndrome studied by massive parallel sequencing, we identified five patients with SCEH and HIBCH deficiency. Fourteen additional patients were recruited through collaborations with other centres. In total, we analysed the neurological features and mutation spectrum in 19 new SCEH/HIBCH patients. For natural history studies and phenotype to genotype associations we also included 70 previously reported patients. The 19 newly identified cases presented with Leigh syndrome (SCEH, n = 11; HIBCH, n = 6) and paroxysmal dystonia (SCEH, n = 2). Basal ganglia lesions (18 patients) were associated with small cysts in the putamen/pallidum in half of the cases, a characteristic hallmark for diagnosis. Eighteen pathogenic variants were identified, 11 were novel. Among all 89 cases, we observed a longer survival in HIBCH compared to SCEH patients, and in HIBCH patients carrying homozygous mutations on the protein surface compared to those with variants inside/near the catalytic region. The SCEH p.(Ala173Val) change was associated with a milder form of paroxysmal dystonia triggered by increased energy demands. In a child harbouring SCEH p.(Ala173Val) and the novel p.(Leu123Phe) change, an 83.6% reduction of the protein was observed in fibroblasts. The SCEH and HIBCH defects in the catabolic valine pathway were a frequent cause of Leigh syndrome in our cohort. We identified phenotype and genotype associations that may help predict outcome and improve clinical management.

Gene Therapy for Neuronopathic Mucopolysaccharidoses: State of the Art.

The need for long-lasting and transformative therapies for mucopolysaccharidoses (MPS) cannot be understated. Currently, many forms of MPS lack a specific treatment and in other cases available therapies, such as enzyme replacement therapy (ERT), do not reach important areas such as the central nervous system (CNS). The advent of newborn screening procedures represents a major step forward in early identification and treatment of individuals with MPS. However, the treatment of brain disease in neuronopathic MPS has been a major challenge to date, mainly because the blood brain barrier (BBB) prevents penetration of the brain by large molecules, including enzymes. Over the last years several novel experimental therapies for neuronopathic MPS have been investigated. Gene therapy and gene editing constitute potentially curative treatments. However, despite recent progress in the field, several considerations should be taken into account. This review focuses on the state of the art of in vivo and ex vivo gene therapy-based approaches targeting the CNS in neuronopathic MPS, discusses clinical trials conducted to date, and provides a vision for the future implications of these therapies for the medical community. Recent advances in the field, as well as limitations relating to efficacy, potential toxicity, and immunogenicity, are also discussed.

HNRNPH1-related syndromic intellectual disability: Seven additional cases suggestive of a distinct syndromic neurodevelopmental syndrome.

Pathogenic variants in HNRNPH1 were first reported in 2018. The reported individual, a 13 year old boy with a c.616C>T (p.R206W) variant in the HNRNPH1 gene, was noted to have overlapping symptoms with those observed in HNRNPH2-related X-linked intellectual disability, Bain type (MRXSB), specifically intellectual disability and dysmorphic features. While HNRNPH1 variants were initially proposed to represent an autosomal cause of MRXSB, we report an additional seven cases which identify phenotypic differences from MRXSB. Patients with HNRNPH1 pathogenic variants diagnosed via WES were identified using clinical networks and GeneMatcher. Features unique to individuals with HNRNPH1 variants include distinctive dysmorphic facial features; an increased incidence of congenital anomalies including cranial and brain abnormalities, genitourinary malformations, and palate abnormalities; increased incidence of ophthalmologic abnormalities; and a decreased incidence of epilepsy and cardiac defects compared to those with MRXSB. This suggests that pathogenic variants in HNRNPH1 result in a related, but distinct syndromic cause of intellectual disability from MRXSB, which we refer to as HNRNPH1-related syndromic intellectual disability.

Gaucher disease type 3c: New patients with unique presentations and review of the literature.

Gaucher disease (GD) is the most prevalent lysosomal disorder caused by GBA mutations and abnormal glucocerebrosidase function, leading to glucocerebrosideaccumulation mainly in the liver, spleen, bone marrow, lungs, and occasionally in the central nervous system. Gaucher disease type 3c (GD3c) is a rare subtype of the subacute/chronic neuronopathic GD3, caused by homozygosity for the GBA p.Asp448His (D409H) mutation. GD3c is characterized mainly by cardiovascular and neuro-ophthalmological findings. In this paper, we describe four new GD3c patients exhibiting rare cardiovascular, pulmonary and psychiatric findings, as well as atypical disease courses. Review of the GD3c-related literature revealed clinical descriptions of 36 patients, presenting predominantly with cardiovascular calcifications; 15%, including Patient 1b in this study, had non-calcified lesions - fibrosis and atherosclerosis. Only 7.5% of patients have been described without heart disease, including Patient 3; however, Patient 2 had a fulminant coronary disease. Neurological findings in GD3c consist mainly of oculomotor apraxia (80%), which is absent in Patient 3, while other neurological findings are common (65%) but diverse. Patient 1b developed a psychiatric behavioral disorder, which has not been previously described in GD3c. Patient 1b also had interstitial lung disease, which was only described in one GD3c patient as pulmonary fibrosis. In view of these unique features, we recommend a revised surveillance protocol; however, further studies are required to establish the management of these patients and the role of GBA in the described pathologies.

Intrathecal heparan-N-sulfatase in patients with Sanfilippo syndrome type A: A phase IIb randomized trial.

BACKGROUND: Sanfilippo syndrome type A (mucopolysaccharidosis type IIIA) is a lysosomal disorder wherein deficient heparan-N-sulfatase (HNS) activity results in the accumulation of heparan sulfate in the central nervous system and is associated with progressive neurodegeneration in early childhood. We report on the efficacy, pharmacokinetics, safety, and tolerability of intrathecal (IT) administration of recombinant human HNS (rhHNS) from a phase IIb randomized open-label trial. METHODS: Twenty-one patients, randomized 1:1:1 to rhHNS IT 45 mg administered every 2 weeks (Q2W), every 4 weeks (Q4W), or no treatment, were assessed for amelioration in neurocognitive decline as determined by the Bayley Scales of Infant and Toddler Development®, Third Edition. The primary efficacy goal was defined as ≤10-point decline (responder) in at least three patients in a dosing cohort after 48 weeks. Other efficacy assessments included adaptive behavioral function, assessments of cortical gray matter volume, and glycosaminoglycan (GAG) levels in urine. RESULTS: A clinical response to rhHNS IT was observed in three treated patients (two in the Q2W group, one in the Q4W group). Cerebrospinal fluid heparan sulfate and urine GAG levels were reduced in all treated patients. However, most secondary efficacy assessments were similar between treated patients (n = 14; age, 17.8-47.8 months) and untreated controls (n = 7; age, 12.6-45.0 months). Treatment-emergent adverse events that occurred with rhHNS IT were mostly mild, none led to study discontinuation, and there were no deaths. CONCLUSION: rhHNS IT treatment reduced heparan sulfate and GAG levels in treated patients. Though the primary neurocognitive endpoint was not met, important lessons in the design and endpoints for evaluation of cognitive and behavioral diseases resulted. TRIAL REGISTRATION: ClinicalTrials.govNCT02060526; EudraCT 2013-003450-24.

Mutations in the mitochondrial complex I assembly factor NDUFAF6 cause isolated bilateral striatal necrosis and progressive dystonia in childhood.

AIM: To perform a deep phenotype characterisation in a pedigree of 3 siblings with Leigh syndrome and compound heterozygous NDUFAF6 mutations. METHOD: A multi-gene panel of childhood-onset basal ganglia neurodegeneration inherited conditions was analysed followed by functional studies in fibroblasts. RESULTS: Three siblings developed gait dystonia in infancy followed by rapid progression to generalised dystonia and psychomotor regression. Brain magnetic resonance showed symmetric and bilateral cytotoxic lesions in the putamen and proliferation of the lenticular-striate arteries, latter spreading to the caudate and progressing to cavitation and volume loss. We identified a frameshift novel change (c.554_558delTTCTT; p.Tyr187AsnfsTer65) and a pathogenic missense change (c.371T>C; p.Ile124Thr) in the NDUFAF6 gene, which segregated with an autosomal recessive inheritance within the family. Patient mutations were associated with the absence of the NDUFAF6 protein and reduced activity and assembly of mature complex I in fibroblasts. By functional complementation assay, the mutant phenotype was rescued by the canonical version of the NDUFAF6. A literature review of 14 NDUFAF6 patients showed a consistent phenotype of an early childhood insidious onset neurological regression with prominent dystonia associated with basal ganglia degeneration and long survival. INTERPRETATION: NDUFAF6-related Leigh syndrome is a relevant cause of childhood onset dystonia and isolated bilateral striatal necrosis. By genetic complementation, we could demonstrate the pathogenicity of novel genetic variants in NDUFAF6.

The Role of Liver Transplantation in Propionic Acidemia.

Despite optimal medical treatment and strict low-protein diet, the prognosis of propionic acidemia (PA) patients is generally poor. We aim to report our experience with liver transplantation (LT) in the management of PA patients. Six patients with PA received a LT at a mean age of 5.2 years (1.3-7.5 years). The indications for LT were frequent metabolic decompensations in the first 4 patients and preventative in the last 2 patients. Two patients presented hepatic artery thromboses that were solved through an interventional radiologist approach. These patients showed a very high procoagulant state that was observed by thromboelastography. Arterial vasospasm without thrombus was observed in 2 patients during the LT surgery. In order to avoid hepatic artery thrombosis, an arterial conduit from the recipient aorta to the hepatic artery of the donor was used in the fifth patient. After LT, patients presented improvement in propionyl byproducts without complete normalization, but no decompensations have been observed. In conclusion, LT could be a good therapeutic option to improve the metabolic control and the quality of life of PA patients. Improved surgical strategies along with new techniques of interventional radiology allow us to perform the LT minimizing the complications derived from the higher risk of hepatic artery thrombosis.

A fatal mitochondrial disease is associated with defective NFU1 function in the maturation of a subset of mitochondrial Fe-S proteins.

We report on ten individuals with a fatal infantile encephalopathy and/or pulmonary hypertension, leading to death before the age of 15 months. Hyperglycinemia and lactic acidosis were common findings. Glycine cleavage system and pyruvate dehydrogenase complex (PDHC) activities were low. Homozygosity mapping revealed a perfectly overlapping homozygous region of 1.24 Mb corresponding to chromosome 2 and led to the identification of a homozygous missense mutation (c.622G > T) in NFU1, which encodes a conserved protein suggested to participate in Fe-S cluster biogenesis. Nine individuals were homozygous for this mutation, whereas one was compound heterozygous for this and a splice-site (c.545 + 5G > A) mutation. The biochemical phenotype suggested an impaired activity of the Fe-S enzyme lipoic acid synthase (LAS). Direct measurement of protein-bound lipoic acid in individual tissues indeed showed marked decreases. Upon depletion of NFU1 by RNA interference in human cell culture, LAS and, in turn, PDHC activities were largely diminished. In addition, the amount of succinate dehydrogenase, but no other Fe-S proteins, was decreased. In contrast, depletion of the general Fe-S scaffold protein ISCU severely affected assembly of all tested Fe-S proteins, suggesting that NFU1 performs a specific function in mitochondrial Fe-S cluster maturation. Similar biochemical effects were observed in Saccharomyces cerevisiae upon deletion of NFU1, resulting in lower lipoylation and SDH activity. Importantly, yeast Nfu1 protein carrying the individuals' missense mutation was functionally impaired. We conclude that NFU1 functions as a late-acting maturation factor for a subset of mitochondrial Fe-S proteins.

Protein expression profiles in patients carrying NFU1 mutations. Contribution to the pathophysiology of the disease.

Cofactor disorders of mitochondrial energy metabolism are a heterogeneous group of diseases with a wide variety of clinical symptoms, particular metabolic profiles and variable enzymatic defects. Mutations in NFU1 were recently identified in patients with fatal encephalopathy displaying a biochemical phenotype consistent with defects in lipoic acid-dependent enzymatic activities and respiratory chain complexes. This discovery highlighted the molecular function of NFU1 as an iron-sulfur(Fe-S) cluster protein necessary for lipoic acid biosynthesis and respiratory chain complexes activities. To understand the pathophysiological mechanisms underlying this disease we have characterized the protein expression profiles of patients carrying NFU1 mutations. Fibroblasts from patients with the p.Gly208Cys mutation showed complete absence of protein-bound lipoic acid and decreased SDHA and SDHB subunits of complex II. In contrast, subunits of other respiratory chain complexes were normal. Protein lipoylation was also decreased in muscle and liver but not in other tissues available (brain, kidney, lung) from NFU1 patients. Although levels of the respiratory chain subunits were unaltered in tissues, BN-PAGE showed an assembly defect for complex II in muscle, consistent with the low enzymatic activity of this complex. This study provides new insights into the molecular bases of NFU1 disease as well as into the regulation of NFU1 protein in human tissues. We demonstrate a ubiquitous expression of NFU1 protein and further suggest that defects in lipoic acid biosynthesis and complex II are the main molecular signature of this disease, particularly in patients carrying the p.Gly208Cys mutation.

ClinPrior: an algorithm for diagnosis and novel gene discovery by network-based prioritization.

BACKGROUND: Whole-exome sequencing (WES) and whole-genome sequencing (WGS) have become indispensable tools to solve rare Mendelian genetic conditions. Nevertheless, there is still an urgent need for sensitive, fast algorithms to maximise WES/WGS diagnostic yield in rare disease patients. Most tools devoted to this aim take advantage of patient phenotype information for prioritization of genomic data, although are often limited by incomplete gene-phenotype knowledge stored in biomedical databases and a lack of proper benchmarking on real-world patient cohorts. METHODS: We developed ClinPrior, a novel method for the analysis of WES/WGS data that ranks candidate causal variants based on the patient's standardized phenotypic features (in Human Phenotype Ontology (HPO) terms). The algorithm propagates the data through an interactome network-based prioritization approach. This algorithm was thoroughly benchmarked using a synthetic patient cohort and was subsequently tested on a heterogeneous prospective, real-world series of 135 families affected by hereditary spastic paraplegia (HSP) and/or cerebellar ataxia (CA). RESULTS: ClinPrior successfully identified causative variants achieving a final positive diagnostic yield of 70% in our real-world cohort. This includes 10 novel candidate genes not previously associated with disease, 7 of which were functionally validated within this project. We used the knowledge generated by ClinPrior to create a specific interactome for HSP/CA disorders thus enabling future diagnoses as well as the discovery of novel disease genes. CONCLUSIONS: ClinPrior is an algorithm that uses standardized phenotype information and interactome data to improve clinical genomic diagnosis. It helps in identifying atypical cases and efficiently predicts novel disease-causing genes. This leads to increasing diagnostic yield, shortening of the diagnostic Odysseys and advancing our understanding of human illnesses.

Molecular analysis of mucopolysaccharidosis IVA (Morquio A) in Spain.

Mucopolysaccharidosis type IVA (Morquio A) is an inherited metabolic disease with autosomal recessive inheritance. The pathology is due to a deficient activity of N-acetylgalactosamine-6-sulfate-sulfatase, which is involved in the degradation of keratan sulfate and chondroitin-6-sulfate. To date more than 150 mutations have been described in the GALNS gene in different populations. The aim of this study was to analyze the mutations and polymorphisms in Spain in order to know the epidemiology of our population and also to offer genetic counseling to affected families. We found 30 mutant alleles in the 15 families analyzed completing all the genotypes. Most of the mutations that we found were missense mutations, six of which were novel: p.S74F, p.E121D, p.Y254C, p.E260K, p.T394P and p.N495Y; we also found a small deletion (c.1142delC) and a probable deep intronic mutation that causes the loss of exon 5 (c.423_566del) found in cDNA. Both mutations are described in this study for the first time. We also identified 20 polymorphisms previously reported and 2 novel ones: (c.633+222T/C and c.898+25C>G). In conclusion, we have identified the mutations responsible for Mucopolysaccharidosis IV A in Spain. We found great allelic heterogeneity, as occurs in other populations, which hinders the establishment of genotype-phenotype correlations in Spain. This study has been very useful for genetic counseling to the affected families.

The LINCE Project: A Pathway for Diagnosing NCL2 Disease.

Introduction: Neuronal Ceroid Lipofuscinosis (NCL) comprises a clinically and genetically heterogeneous group of 13 neurodegenerative lysosomal storage disorders. Neuronal Ceroid lipofuscinosis type 2 disease (NCL2), caused by the deficient lysosomal enzyme tripeptidyl peptidase 1 (TPP1), is the only one with an approved enzyme replacement treatment (ERT). Early initiation of ERT appears to modify significantly the natural history of the disease. We aimed to shorten the time to diagnosis of NCL2. Methods: In March 2017, we started per first time in Spain a selective screening program, the LINCE project, in pediatric patients with clinical symptoms compatible with NCL2 disease. The program covered the whole country. We distributed kits to pediatricians with the necessary material to assess patients. All samples in this study were received within one week of collection. Enzymatic activity determined on dried blood spots was the main method used to screen for TPP1 and palmitoyl protein thioesterase 1 (PPT1) for the differential diagnosis with neuronal ceroid lipofuscinosis type 1 (NCL1). Results: Over a period of three years, we received 71 samples. The analysis was minimally invasive, relatively cheap and fast-executing. Three cases identified as a direct result of the selective screening strategy were confirmed by genetic study of NCL2 disease with a median age of 4.5 years. Our screening method has a specificity of 100%, and, with the absence to date of false negatives. We did not detect any NCL1-positive cases. Conclusions: LINCE proved to be a simple, useful, and reliable tool for the diagnosis of NCL2, enabling clinicians to diagnose NCL2 faster. The presence of NCL2-positive cases in our population and availability of treatment may facilitate the inclusion of NCL2 in neonatal screening programs for early diagnosis.

Diagnosis of Genetic White Matter Disorders by Singleton Whole-Exome and Genome Sequencing Using Interactome-Driven Prioritization.

BACKGROUND AND OBJECTIVES: Genetic white matter disorders (GWMD) are of heterogeneous origin, with >100 causal genes identified to date. Classic targeted approaches achieve a molecular diagnosis in only half of all patients. We aimed to determine the clinical utility of singleton whole-exome sequencing and whole-genome sequencing (sWES-WGS) interpreted with a phenotype- and interactome-driven prioritization algorithm to diagnose GWMD while identifying novel phenotypes and candidate genes. METHODS: A case series of patients of all ages with undiagnosed GWMD despite extensive standard-of-care paraclinical studies were recruited between April 2017 and December 2019 in a collaborative study at the Bellvitge Biomedical Research Institute (IDIBELL) and neurology units of tertiary Spanish hospitals. We ran sWES and WGS and applied our interactome-prioritization algorithm based on the network expansion of a seed group of GWMD-related genes derived from the Human Phenotype Ontology terms of each patient. RESULTS: We evaluated 126 patients (101 children and 25 adults) with ages ranging from 1 month to 74 years. We obtained a first molecular diagnosis by singleton WES in 59% of cases, which increased to 68% after annual reanalysis, and reached 72% after WGS was performed in 16 of the remaining negative cases. We identified variants in 57 different genes among 91 diagnosed cases, with the most frequent being RNASEH2B, EIF2B5, POLR3A, and PLP1, and a dual diagnosis underlying complex phenotypes in 6 families, underscoring the importance of genomic analysis to solve these cases. We discovered 9 candidate genes causing novel diseases and propose additional putative novel candidate genes for yet-to-be discovered GWMD. DISCUSSION: Our strategy enables a high diagnostic yield and is a good alternative to trio WES/WGS for GWMD. It shortens the time to diagnosis compared to the classical targeted approach, thus optimizing appropriate management. Furthermore, the interactome-driven prioritization pipeline enables the discovery of novel disease-causing genes and phenotypes, and predicts novel putative candidate genes, shedding light on etiopathogenic mechanisms that are pivotal for myelin generation and maintenance.

Switching to Glycerol Phenylbutyrate in 48 Patients with Urea Cycle Disorders: Clinical Experience in Spain.

Background and objectives: Glycerol phenylbutyrate (GPB) has demonstrated safety and efficacy in patients with urea cycle disorders (UCDs) by means of its clinical trial program, but there are limited data in clinical practice. In order to analyze the efficacy and safety of GPB in clinical practice, here we present a national Spanish experience after direct switching from another nitrogen scavenger to GPB. Methods: This observational, retrospective, multicenter study was performed in 48 UCD patients (age 11.7 ± 8.2 years) switching to GPB in 13 centers from nine Spanish regions. Clinical, biochemical, and nutritional data were collected at three different times: prior to GPB introduction, at first follow-up assessment, and after one year of GPB treatment. Number of related adverse effects and hyperammonemic crisis 12 months before and after GPB introduction were recorded. Results: GPB was administered at a 247.8 ± 102.1 mg/kg/day dose, compared to 262.6 ± 126.1 mg/kg/day of previous scavenger (46/48 Na-phenylbutyrate). At first follow-up (79 ± 59 days), a statistically significant reduction in ammonia (from 40.2 ± 17.3 to 32.6 ± 13.9 µmol/L, p < 0.001) and glutamine levels (from 791.4 ± 289.8 to 648.6 ± 247.41 µmol/L, p < 0.001) was observed. After one year of GPB treatment (411 ± 92 days), we observed an improved metabolic control (maintenance of ammonia and glutamine reduction, with improved branched chain amino acids profile), and a reduction in hyperammonemic crisis rate (from 0.3 ± 0.7 to less than 0.1 ± 0.3 crisis/patients/year, p = 0.02) and related adverse effects (RAE, from 0.5 to less than 0.1 RAEs/patients/year p < 0.001). Conclusions: This study demonstrates the safety of direct switching from other nitrogen scavengers to GPB in clinical practice, which improves efficacy, metabolic control, and RAE compared to previous treatments.

Tyrosinemia type 1 in Spain: mutational analysis, treatment and long-term outcome.

BACKGROUND: Tyrosinemia type 1 (HT1) is a rare but treatable disease. The aim of the present study was to review the efficacy of long-term treatment of HT1 with nitisinone, expand knowledge about the clinical spectrum of the disease and assess a possible genotype-phenotype correlation. METHODS: A retrospective multicenter study was carried out based on questionnaires on genotype, phenotype, therapy and outcome in 34 Spanish patients with HT1. RESULTS: The main manifestations that led to the diagnosis were acute liver failure (55.8%), asymptomatic hepatomegaly (44.1%) and renal tubular dysfunction (29.4%). Laboratory analysis indicated a marked increase of α-fetoprotein and coagulopathy. The most common mutation was IVS6-1(G > T; 66.6% of 24/34 patients for whom mutation analysis was available) and these patients presented less nephrocalcinosis and more hepatomegaly at diagnosis; two novel mutations (c.974C>T, c.398A>T) were found. The mean duration of treatment was 6.73 years. Dietary compliance was very good in 47.1% and good in 20.6%; nitisinone treatment adherence was very good in 85.2% of cases. Mean dose of nitisinone was 0.87 mg/kg per day with average plasma levels of 45.67 µmol/L. Only one patient required liver transplantation after nitisinone and none had hepatocellular carcinoma. CONCLUSIONS: Treatment with nitisinone has improved the prognosis of HT1, and compliance is good. In Spain, screening for HT1 by plasma tyrosine and urine succinylacetone determination may be implemented with IVS6-1(G > T) mutational analysis. A correlation between low frequency of nephrocalcinosis and IVS6-1(G > T) mutation was observed.