Project GIVE: using a virtual genetics service platform to reduce health inequities and improve access to genomic care in an underserved region of Texas.

BACKGROUND: The utilization of genomic information to improve health outcomes is progressively becoming more common in clinical practice. Nonetheless, disparities persist in accessing genetic services among ethnic minorities, individuals with low socioeconomic status, and other vulnerable populations. The Rio Grande Valley (RGV) at the Texas-Mexico border is predominantly Hispanic/Latino with a high poverty rate and very limited access to genetic services. Funded by the National Center for Advancing Translational Sciences, Project GIVE (Genetic Inclusion by Virtual Evaluation) was launched in 2022 to reduce the time to diagnosis and increase provider knowledge of genomics in this region, with the goal of improving pediatric health outcomes. We describe our experience of establishing a virtual pediatric genomic service in this region to expeditiously identify, recruit, and evaluate pediatric patients with undiagnosed diseases. METHODS: We have utilized an innovative electronic health record (EHR) agnostic virtual telehealth and educational platform called Consultagene to receive referrals from healthcare providers in the RGV. Using this portal, genetic services, including virtual evaluation and genome sequencing (GS), are being delivered to children with rare diseases. The study has also integrated effective methods to involve and educate community providers through in-person meetings and Continuing Professional Education (CPE) events. RESULTS: The recruitment efforts have proven highly successful with the utilization of Consultagene in this medically underserved region. The project's ongoing engagement efforts with local healthcare providers have resulted in progressively more referrals to the study over time, thus improving inclusion and access to genomic care in the RGV. Additionally, the curated CPE content has been well received by healthcare providers in the region. CONCLUSIONS: Project GIVE study has allowed advanced genetic evaluation and delivery of GS through the virtual Consultagene portal, effectively circumventing the recognized socioeconomic and logistical barriers to accessing genetic services within this border community.

Natural history study of hepatic glycogen storage disease type IV and comparison to Gbe1ys/ys model.

BackgroundGlycogen storage disease type IV (GSD IV) is an ultrarare autosomal recessive disorder that causes deficiency of functional glycogen branching enzyme and formation of abnormally structured glycogen termed polyglucosan. GSD IV has traditionally been categorized based on primary hepatic or neuromuscular involvement, with hepatic GSD IV subclassified as discrete subtypes: classic (progressive) and nonprogressive.MethodsTo better understand the progression of liver disease in GSD IV, we present clinical and histopathology data from 23 patients from around the world and characterized the liver involvement in the Gbe1ys/ys knockin mouse model.ResultsWe propose an alternative to the established subtype-based terminology for characterizing liver disease in GSD IV and recognize 3 tiers of disease severity: (i) "severe progressive" liver disease, (ii) "intermediate progressive" liver disease, and (iii) "attenuated" liver disease. Analysis of liver pathology revealed that risk for liver failure cannot be predicted from liver biopsy findings alone in individuals affected by GSD IV. Moreover, analysis of postmortem liver pathology from an individual who died over 40 years after being diagnosed with nonprogressive hepatic GSD IV in childhood verified that liver fibrosis did not regress. Last, characterization of the liver involvement in a mouse model known to recapitulate the adult-onset neurodegenerative form of GSD IV (Gbe1ys/ys mouse model) demonstrated hepatic disease.ConclusionOur findings challenge the established subtype-based view of GSD IV and suggest that liver disease severity among patients with GSD IV represents a disease continuum.Trial registrationClinicalTrials.gov NCT02683512FundingNone.

Diagnosis and management of glycogen storage disease type IV, including adult polyglucosan body disease: A clinical practice resource.

Glycogen storage disease type IV (GSD IV) is an ultra-rare autosomal recessive disorder caused by pathogenic variants in GBE1 which results in reduced or deficient glycogen branching enzyme activity. Consequently, glycogen synthesis is impaired and leads to accumulation of poorly branched glycogen known as polyglucosan. GSD IV is characterized by a remarkable degree of phenotypic heterogeneity with presentations in utero, during infancy, early childhood, adolescence, or middle to late adulthood. The clinical continuum encompasses hepatic, cardiac, muscular, and neurologic manifestations that range in severity. The adult-onset form of GSD IV, referred to as adult polyglucosan body disease (APBD), is a neurodegenerative disease characterized by neurogenic bladder, spastic paraparesis, and peripheral neuropathy. There are currently no consensus guidelines for the diagnosis and management of these patients, resulting in high rates of misdiagnosis, delayed diagnosis, and lack of standardized clinical care. To address this, a group of experts from the United States developed a set of recommendations for the diagnosis and management of all clinical phenotypes of GSD IV, including APBD, to support clinicians and caregivers who provide long-term care for individuals with GSD IV. The educational resource includes practical steps to confirm a GSD IV diagnosis and best practices for medical management, including (a) imaging of the liver, heart, skeletal muscle, brain, and spine, (b) functional and neuromusculoskeletal assessments, (c) laboratory investigations, (d) liver and heart transplantation, and (e) long-term follow-up care. Remaining knowledge gaps are detailed to emphasize areas for improvement and future research.

Natural history of TANGO2 deficiency disorder: Baseline assessment of 73 patients.

PURPOSE: TANGO2 deficiency disorder (TDD), an autosomal recessive disease first reported in 2016, is characterized by neurodevelopmental delay, seizures, intermittent ataxia, hypothyroidism, and life-threatening metabolic and cardiac crises. The purpose of this study was to define the natural history of TDD. METHODS: Data were collected from an ongoing natural history study of patients with TDD enrolled between February 2019 and May 2022. Data were obtained through phone or video based parent interviews and medical record review. RESULTS: Data were collected from 73 patients (59% male) from 57 unrelated families living in 16 different countries. The median age of participants at the time of data collection was 9.0 years (interquartile range = 5.3-15.9 years, range = fetal to 31.8 years). A total of 24 different TANGO2 alleles were observed. Patients showed normal development in early infancy, with progressive delay in developmental milestones thereafter. Symptoms included ataxia, dystonia, and speech difficulties, typically starting between the ages of 1 to 3 years. A total of 46/71 (65%) patients suffered metabolic crises, and of those, 30 (65%) developed cardiac crises. Metabolic crises were significantly decreased after the initiation of B-complex or multivitamin supplementation. CONCLUSION: We provide the most comprehensive review of natural history of TDD and important observational data suggesting that B-complex or multivitamins may prevent metabolic crises.

Reducing Time to Diagnosis of Rare Genetic Diseases in a Medically Underserved Hispanic Population- Lessons Learned for Meaningful Engagement.

Background: The utilization of genomic information to improve health outcomes is progressively becoming more common in clinical practice. Nonetheless, disparities persist in accessing genetic services among ethnic minorities, individuals with low socioeconomic status, and other vulnerable populations. The Rio Grande Valley at the Texas-Mexico border is predominantly Hispanic with a high poverty rate and an increased prevalence of birth defects, with very limited access to genetics services. The cost of a diagnosis is often times out of reach for these underserved families. Funded by the National Center for Advancing Translational Sciences (NCATS), Project GIVE (Genetic Inclusion by Virtual Evaluation) was launched in 2022 to shorten the time to diagnosis and alleviate healthcare inequities in this region, with the goal of improving pediatric health outcomes. Methods: Utilizing Consultagene, an innovative electronic health record (EHR) agnostic virtual telehealth and educational platform, we designed the study to recruit 100 children with rare diseases over a period of two years from this region, through peer-to-peer consultation and referral. Conclusions: Project GIVE study has allowed advanced genetic evaluation and delivery of genome sequencing through the virtual portal, effectively circumventing the recognized socioeconomic and other barriers within this population. This paper explores the successful community engagement process and implementation of an alternate genomics evaluation platform and testing approach, aiming to reduce the diagnostic journey for individuals with rare diseases residing in a medically underserved region.

Untargeted metabolomic profiling in a patient with glycogen storage disease Ib receiving empagliflozin treatment.

Glycogen storage disease type Ib (GSD-Ib) is a rare inborn error of glycogen metabolism uniquely associated with neutropenia and neutrophil dysfunction, causing severe infections, inflammatory bowel disease (IBD), and impaired wound healing. Recently, kidney sodium-glucose co-transporter-2 (SGLT2) inhibitors such as empagliflozin known to reduce plasma levels of 1,5-anhydroglucitol (1,5-AG) and its toxic derivatives in neutrophils, have been described as a new treatment option in case reports of patients with GSD-Ib from Europe and Asia. We report our experience with an 11-year-old girl with GSD-Ib presenting with short fasting hypoglycemia, neutropenia with neutrophil dysfunction, recurrent infections, suboptimal growth, iron-deficiency anemia, and IBD. Treatment with daily empagliflozin improved neutrophil counts and function with a significant reduction in G-CSF needs. Significant improvement in IBD has led to weight gain with improved nutritional markers and improved fasting tolerance. Reduction of maximum empagliflozin dose was needed due to arthralgia. No other significant side effects of empagliflozin were observed. This report uniquely highlights the novel use of untargeted metabolomics profiling for monitoring plasma levels of 1,5-AG to assess empagliflozin dose responsiveness and guide dietary management and G-CSF therapy. Clinical improvement correlated to rapid normalization of 1,5-AG levels in plasma sustained after dose reduction. In conclusion, empagliflozin appeared to be a safe treatment option for GSD-Ib-associated neutropenia and neutrophil dysfunction. Global untargeted metabolomics is an efficient method to assess biochemical responsiveness to treatment.

Cardiac crises: Cardiac arrhythmias and cardiomyopathy during TANGO2 deficiency related metabolic crises.

BACKGROUND: TANGO2 deficiency disorder (TDD) is an autosomal recessive disease associated with metabolic crisis, lethal cardiac arrhythmias, and cardiomyopathy. Data regarding treatment, management, and outcomes of cardiac manifestations of TDD are lacking. OBJECTIVE: The purpose of this study was to describe TDD-related cardiac crises. METHODS: Retrospective multicenter chart review was made of TDD patients admitted with cardiac crises, defined as development of ventricular tachycardia (VT), cardiomyopathy, or cardiac arrest during metabolic crises. RESULTS: Twenty-seven children were admitted for 43 cardiac crises (median age 6.4 years; interquartile range [IQR] 2.4-9.8 years) at 14 centers. During crisis, QTc prolongation occurred in all (median 547 ms; IQR 504-600 ms) and a type I Brugada pattern in 8 (26%). Arrhythmias included VT in 21 (78%), supraventricular tachycardia in 3 (11%), and heart block in 1 (4%). Nineteen patients (70%) developed cardiomyopathy, and 20 (74%) experienced a cardiac arrest. There were 10 deaths (37%), 6 related to arrhythmias. In 5 patients, recalcitrant VT occurred despite use of antiarrhythmic drugs. In 6 patients, arrhythmias were controlled after extracorporeal membrane oxygenation (ECMO) support; 5 of these patients survived. Among 10 patients who survived VT without ECMO, successful treatment included intravenous magnesium, isoproterenol, and atrial pacing in multiple cases and verapamil in 1 patient. Initiation of feeds seemed to decrease VT events. CONCLUSION: TDD-related cardiac crises are associated with a high risk of arrhythmias, cardiomyopathy, cardiac arrest, and death. Although further studies are needed, early recognition and appropriate treatment are critical. Acutely, intravenous magnesium, isoproterenol, atrial pacing, and ECMO as a last resort seem to be the best current treatment options, and early initiation of feeds may prevent VT events.

Exome sequencing in children with clinically suspected maturity-onset diabetes of the young.

OBJECTIVE: Commercial gene panels identify pathogenic variants in as low as 27% of patients suspected to have MODY, suggesting the role of yet unidentified pathogenic variants. We sought to identify novel gene variants associated with MODY. RESEARCH DESIGN AND METHODS: We recruited 10 children with a clinical suspicion of MODY but non-diagnostic commercial MODY gene panels. We performed exome sequencing (ES) in them and their parents. RESULTS: Mean age at diabetes diagnosis was 10 (± 3.8) years. Six were females; 4 were non-Hispanic white, 5 Hispanic, and 1 Asian. Our variant prioritization analysis identified a pathogenic, de novo variant in INS (c.94G > A, p.Gly32Ser), confirmed by Sanger sequencing, in a proband who was previously diagnosed with "autoantibody-negative type 1 diabetes (T1D)" at 3 y/o. This rare variant, absent in the general population (gnomAD database), has been reported previously in neonatal diabetes. We also identified a frameshift deletion (c.2650delC, p.Gln884AsnfsTer57) in RFX6 in a child with a previous diagnosis of "autoantibody-negative T1D" at 12 y/o. The variant was inherited from the mother, who was diagnosed with "thin type 2 diabetes" at 25 y/o. Heterozygous protein-truncating variants in RFX6 gene have been recently reported in individuals with MODY. CONCLUSIONS: We diagnosed two patients with MODY using ES in children initially classified as "T1D". One has a likely pathogenic novel gene variant not previously associated with MODY. We demonstrate the clinical utility of ES in patients with clinical suspicion of MODY.

PPP3CA truncating variants clustered in the regulatory domain cause early-onset refractory epilepsy.

PPP3CA encodes the catalytic subunit of calcineurin, a calcium-calmodulin-regulated serine-threonine phosphatase. Loss-of-function (LoF) variants in the catalytic domain have been associated with epilepsy, while gain-of-function (GoF) variants in the auto-inhibitory domain cause multiple congenital abnormalities. We herein report five new patients with de novo PPP3CA variants. Interestingly, the two frameshift variants in this study and the six truncating variants reported previously are all located within a 26-amino acid region in the regulatory domain (RD). Patients with a truncating variant had more severe earlier onset seizures compared to patients with a LoF missense variant, while autism spectrum disorder was a more frequent feature in the latter. Expression studies of a truncating variant showed apparent RNA expression from the mutant allele, but no detectable mutant protein. Our data suggest that PPP3CA truncating variants clustered in the RD, causing more severe early-onset refractory epilepsy and representing a type of variants distinct from LoF or GoF missense variants.

Acute Strokelike Presentation and Long-term Evolution of Diffusion Restriction Pattern in Ethylmalonic Encephalopathy.

Ethylmalonic encephalopathy is a rare autosomal recessive mitochondrial disorder caused by pathogenic biallelic variants in the ETHE1 gene. The phenotype of this disease has been attributed to deficiency in the mitochondrial sulfur dioxygenase leading to many downstream effects. Ethylmalonic encephalopathy classically presents with developmental regression, petechiae, acrocyanosis, and chronic diarrhea. The neurologic phenotype includes hypotonia, spastic diplegia, ataxia, and developmental delay. As more patients with this condition are described, the neurologic phenotype continues to expand. Although strokelike episodes or metabolic strokes have been studied in other mitochondrial disorders, they have not been thoroughly reported in this disorder. Herein, we describe 3 patients with ethylmalonic encephalopathy who presented clinically with strokelike episodes and strokelike abnormalities on brain magnetic resonance imaging in the setting of acute illness, and the long-term sequelae with evolution into cystic changes in one of these subjects.

TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.

TRMU is a nuclear gene crucial for mitochondrial DNA translation by encoding tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase, which thiolates mitochondrial tRNA. Biallelic pathogenic variants in TRMU are associated with transient infantile liver failure. Other less common presentations such as Leigh syndrome, myopathy, and cardiomyopathy have been reported. Recent studies suggested that provision of exogenous L-cysteine or N-acetylcysteine may ameliorate the effects of disease-causing variants and improve the natural history of the disease. Here, we report six infants with biallelic TRMU variants, including four previously unpublished patients, all treated with exogenous cysteine. We highlight the first report of an affected patient undergoing orthotopic liver transplantation, the long-term effects of cysteine supplementation, and the ability of the initial presentation to mimic multiple inborn errors of metabolism. We propose that TRMU deficiency should be suspected in all children presenting with persistent lactic acidosis and hypoglycemia, and that combined N-acetylcysteine and L-cysteine supplementation should be considered prior to molecular diagnosis, as this is a low-risk approach that may increase survival and mitigate the severity of the disease course.

Clinical trials in mitochondrial disorders, an update.

Mitochondrial disorders comprise a molecular and clinically diverse group of diseases that are associated with mitochondrial dysfunction leading to multi-organ disease. With recent advances in molecular technologies, the understanding of the pathomechanisms of a growing list of mitochondrial disorders has been greatly expanded. However, the therapeutic approaches for mitochondrial disorders have lagged behind with treatment options limited mainly to symptom specific therapies and supportive measures. There is an increasing number of clinical trials in mitochondrial disorders aiming for more specific and effective therapies. This review will cover different treatment modalities currently used in mitochondrial disorders, focusing on recent and ongoing clinical trials.

Short stature and growth hormone deficiency in a subset of patients with Potocki-Lupski syndrome: Expanding the phenotype of PTLS.

Potocki-Lupski Syndrome (PTLS, MIM 610883), or duplication of chromosome 17p11.2, is a clinically recognizable condition characterized by infantile hypotonia, failure to thrive, developmental delay, intellectual disability, and congenital anomalies. Short stature, classified as greater than two standard deviations below the mean, has not previously been considered a major feature of PTLS. Retrospective chart review on a cohort of 37 individuals with PTLS was performed to investigate the etiology of short stature. Relevant data included anthropometric measurements, insulin growth factor-1 (IGF-1), insulin-like growth factor binding protein 3 (IGFBP-3), growth hormone (GH) stimulation testing, blood glucose levels, brain MRI, and bone age. Approximately 25% (9/37) of individuals with PTLS had short stature. Growth hormone deficiency (GHD) was definitively identified in two individuals. These two PTLS patients with growth hormone deficiency, as well as three others with short stature and no documented GHD, received growth hormone and obtained improvement in linear growth. One individual was identified to have pituitary abnormalities on MRI and had complications of hypoglycemia due to unrecognized GHD. Individuals with PTLS can benefit from undergoing evaluation for GHD should they present with short stature or hypoglycemia. Early identification of GHD could facilitate potential therapeutic benefit for individuals with PTLS, including linear growth, musculoskeletal, and in cases of hypoglycemia, potentially cognitive development as well.

De Novo Variants in CNOT1, a Central Component of the CCR4-NOT Complex Involved in Gene Expression and RNA and Protein Stability, Cause Neurodevelopmental Delay.

CNOT1 is a member of the CCR4-NOT complex, which is a master regulator, orchestrating gene expression, RNA deadenylation, and protein ubiquitination. We report on 39 individuals with heterozygous de novo CNOT1 variants, including missense, splice site, and nonsense variants, who present with a clinical spectrum of intellectual disability, motor delay, speech delay, seizures, hypotonia, and behavioral problems. To link CNOT1 dysfunction to the neurodevelopmental phenotype observed, we generated variant-specific Drosophila models, which showed learning and memory defects upon CNOT1 knockdown. Introduction of human wild-type CNOT1 was able to rescue this phenotype, whereas mutants could not or only partially, supporting our hypothesis that CNOT1 impairment results in neurodevelopmental delay. Furthermore, the genetic interaction with autism-spectrum genes, such as ASH1L, DYRK1A, MED13, and SHANK3, was impaired in our Drosophila models. Molecular characterization of CNOT1 variants revealed normal CNOT1 expression levels, with both mutant and wild-type alleles expressed at similar levels. Analysis of protein-protein interactions with other members indicated that the CCR4-NOT complex remained intact. An integrated omics approach of patient-derived genomics and transcriptomics data suggested only minimal effects on endonucleolytic nonsense-mediated mRNA decay components, suggesting that de novo CNOT1 variants are likely haploinsufficient hypomorph or neomorph, rather than dominant negative. In summary, we provide strong evidence that de novo CNOT1 variants cause neurodevelopmental delay with a wide range of additional co-morbidities. Whereas the underlying pathophysiological mechanism warrants further analysis, our data demonstrate an essential and central role of the CCR4-NOT complex in human brain development.

Survival and Neurologic Recovery After Prompt Diagnosis and Aggressive Management of Severe Idiopathic Hyperammonemic Encephalopathy in a Patient with Acute Myeloid Leukemia.

A case of a 19-year-old female with low-risk acute myeloid leukemia is presented who was diagnosed with idiopathic hyperammonemic encephalopathy following the development of abrupt neurologic decline, respiratory alkalosis, and elevated plasma ammonia levels of unknown etiology. Delayed symptom recognition of this exceedingly rare condition contributes to the often fatal outcomes of idiopathic hyperammonemic encephalopathy. As illustrated by this case, prompt diagnosis and utilization of a variety of ammonia-modulating treatment modalities can result in remarkable clinical recovery. This case provides guidance to clinicians in counseling families about the possibility of neurologic recovery in similar clinical scenarios.

Liver transplantation in propionic and methylmalonic acidemia: A single center study with literature review.

BACKGROUND: Organic acidemias, especially propionic acidemia (PA) and methylmalonic acidemia (MMA), may manifest clinically within the first few hours to days of life. The classic presentation in the newborn period includes metabolic acidosis, hyperlactatemia, and hyperammonemia that is precipitated by unrestricted protein intake. Implementation of newborn screening to diagnose and initiate early treatment has facilitated a reduction in neonatal mortality and improved survival. Despite early diagnosis and appropriate management, these individuals are prone to have recurrent episodes of metabolic acidosis and hyperammonemia resulting in frequent hospitalizations. Liver transplantation (LT) has been proposed as a treatment modality to reduce metabolic decompensations which are not controlled by medical management. Published reports on the outcome of LT show heterogeneous results regarding clinical and biochemical features in the post transplantation period. As a result, we evaluated the outcomes of LT in our institution and compared it to the previously published data. STUDY DESIGN/METHODS: We performed a retrospective chart review of nine individuals with PA or MMA who underwent LT and two individuals with MMA who underwent LT and kidney transplantation (KT). Data including number of hospitalizations, laboratory measures, cardiac and neurological outcomes, dietary protein intake, and growth parameters were collected. RESULTS: The median age of transplantation for subjects with MMA was 7.2 years with a median follow up of 4.3 years. The median age of transplantation for subjects with PA was 1.9 years with a median follow up of 5.4 years. The survival rate at 1 year and 5 years post-LT was 100%. Most of our subjects did not have any episodes of hyperammonemia or pancreatitis post-LT. There was significant reduction in plasma glycine post-LT. One subject developed mild elevation in ammonia post-LT on an unrestricted protein diet, suggesting that protein restriction may be indicated even after LT. CONCLUSION: In a large single center study of LT in MMA and PA, we show that LT may reduce the incidence of metabolic decompensation. Moreover, our data suggest that LT may be associated with reduced number of hospitalizations and improved linear growth in individuals with PA and MMA.

Case report and novel treatment of an autosomal recessive Leigh syndrome caused by short-chain enoyl-CoA hydratase deficiency.

Short chain enoyl-CoA hydratase (SCEH) deficiency leads to a severe form of autosomal recessive Leigh syndrome with inevitable neurological decline and early mortality. SCEH is most notably involved in valine catabolism, a deficiency of which results in various metabolic alterations, including increased levels of the highly reactive metabolite 2-methacrylyl-CoA. With no proven treatments available to date, it has been speculated that patients may respond to a valine restricted diet and/or N-acetylcysteine supplementation, as suggested by early studies of a very similar inborn error of metabolism, 3-hydroxyisobutyryl-CoA hydrolase deficiency. We describe a patient with typical Leigh syndrome clinical findings and identified compound heterozygous variants in ECSH1. Valine-restricted diet was initiated at 6 months of age and N-acetylcysteine supplementation at 9 months with subsequent improvement in growth and slow progress in developmental milestones. However, at 15 months, the patient aspirated during a breakthrough seizure from which he did not recover and died soon after from related complications. This report highlights some of the challenges that remain in the management and treatment of SCEH deficiency, while demonstrating that a valine restricted diet and N-acetylcysteine can be safely administered with the potential for clinical improvement.

L-Cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.

Early recognition of rare mitochondrial respiratory chain defects has become readily available with the routine use of whole exome sequencing. Patients with oxidative phosphorylation defects present with a heterogenous phenotype, often rapidly progressive, and lethal. Clinicians aim for prompt identification of the specific molecular defect to provide timely management, decrease morbidity, and potentially improve survival rates. More recently, bi-allelic pathogenic variants in the TRMU gene responsible for encoding the mitochondrial tRNA-specific 2-thiouridylase were found in a syndrome characterized by infantile hepatopathy due to a mitochondrial translation defect (OMIM# 613070). This nuclear encoded enzyme catalyzes the addition of a sulfur-containing thiol group to the wobble position of mitochondrial specific tRNAs. TRMU deficiency is characterized by a combined respiratory chain deficiency without associated mitochondrial DNA depletion. This mitochondrial tRNA-modifying enzyme requires sulfur for its activity. Previous cellular models have suggested supplementation with cysteine, one of the sulfur containing amino acids, may play a role in increasing thiouridylation levels of mt-tRNAs by increasing sulfur availability for TRMU activity. Cysteine is considered a conditional essential amino acid due to limited availability in infants caused by immature cystathionine gamma-lyase (cystathionase) enzyme activity. The potential benefit of L-cysteine supplementation in TRMU deficiency has been previously proposed to ameliorate the severity and insidious course of the disease. Here we report the clinical, biochemical, and genetic findings of two siblings presenting with hepatopathy associated with hyperlactatemia due to bi-allelic pathogenic variants in TRMU. One patient died due to related complications. The other case was diagnosed prenatally allowing early implementation of L-cysteine supplementation, recovery of liver function, and avoidance of liver transplantation.

Identification of HIBCH gene mutations causing autosomal recessive Leigh syndrome: a gene involved in valine metabolism.

BACKGROUND: Leigh syndrome is a progressive neurodegenerative disorder with usual onset of symptoms during the first year of life. The disorder has been associated with mutations in over 30 genes. This difficulty with genetic heterogeneity makes whole exome sequencing a more cost-effective approach for investigation of etiology. PATIENT AND RESULTS: We describe an individual with typical Leigh syndrome who was found to have compound heterozygous mutations in the gene HIBCH (3-hydroxyisobutyryl coenzyme A hydrolase), an enzyme involved in the catabolism of valine. She exhibited significant clinical improvement after a valine-restricted diet. CONCLUSIONS: A subset of patients with uncharacterized Leigh syndrome present with specific biochemical abnormalities. This report highpoints the challenges and restrictions of routine metabolic testing and features the recognition of inborn errors of metabolism as potential treatable causes of Leigh syndrome.

Improved standards for prenatal diagnosis of citrullinemia.

Citrullinemia type I is a urea cycle disorder caused by autosomal recessive mutations in argininosuccinate synthetase 1 (ASS1). In the classical form of this disease, symptoms manifest during the neonatal period as progressive lethargy, poor feeding, and central nervous system depression secondary to hyperammonemia. In pregnancies involving two carrier parents, prenatal diagnosis is important for both reproductive decisions and advanced preparation for neonatal care. The current gold standard for prenatal diagnosis has been the citrulline incorporation assay in addition to DNA mutation analysis. Herein, we review our experience with prenatal diagnosis of citrullinemia type I over the span of 11 years in 41 at-risk pregnancies. During this time, we identified 15 affected fetuses using a combination of molecular and biochemical testing. Given the established limitations of both the citrulline incorporation assay as well DNA mutation analysis, we probed our data to assess the value of amniotic fluid amino acid levels in prenatal diagnosis. Previous publications have proposed using the amniotic fluid ratio of citrulline/(arginine+ornithine) in prenatal diagnosis; however, we noted that amniotic fluid arginine levels were normal in our cohort and hypothesized that the amniotic fluid citrulline/ornithine ratio may be superior. Indeed, our analyses revealed that the ratio of amniotic fluid citrulline/ornithine alone correctly distinguished affected from unaffected fetuses in all cases. During the establishment of a normal reference range we discovered significant elevations in amniotic fluid citrulline levels in at-risk pregnancies compared to the normal population even when the fetus was unaffected. This highlights the importance of using amniotic fluid from carrier mothers when setting up a normal reference range. Finally, we report our experience as one of the first centers to adopt Sanger sequencing for prospective prenatal diagnosis of citrullinemia. While this is clearly a useful tool in many cases, we encountered families for whom molecular analysis uncovered variants of unknown clinical significance or no mutation at all. Based upon these new findings, we recommend a combinatorial approach involving ASS1 sequencing and amniotic fluid citrulline/ornithine for the prenatal diagnosis of citrullinemia type I.