Molecular basis of intermittent maple syrup urine disease: novel mutations in the E2 gene of the branched-chain α-keto acid dehydrogenase complex

The E2 gene of the branched-chain α-keto acid dehydrogenase (BCKDH) complex was studied at the molecular level in three patients with intermittent maple syrup urine disease (MSUD). All three patients had higher BCKDH activity than did those with the classical phenotype. In the first patient, a single base substitution from A to G in intron 8 created a new 5′ splice site and caused an insertion of 126 nucleotides between exons 8 and 9 by activating an upstream cryptic 3′ splice site in the same intron. The predicted mRNA encoded a truncated protein with 282 amino acids including 4 novel ones at the carboxyl terminus, compared with the normal protein with 421 amino acids. In vitro, the region from the patient but not from a normal control was recognized and was recovered as a novel exon, indicating that the single substitution was responsible for incorporation of the region into mRNA. This mutation probably supports an exon definition model in which the spliceosome recognizes a 3′ splice site and then scans downstream for an acceptable 5′ splice site, thereby defining an exon. The second patient was homozygous for a G to T transversion at nucleotide 1463 in exon 11, which predicted a substitution of the termination codon by a leucine residue and the addition of 7 extra amino acids at the carboxyl terminus. For each mutation, these two patients were homozygous and their parents were heterozygous. The third patient was a compound heterozygote for a C to G transversion at nucleotide 309 in exon 4 and a G to A transition at nucleotide 1165 in exon 9, causing an Ile-to-Met substitution at amino acid 37 and a Gly-to-Ser substitution at amino acid 323, respectively. Taken together, these results indicate that the molecular basis of intermittent phenotype MSUD in some patients can be due to mutations in the E2 gene, giving rise to a low but significant residual activity of the BCKDH complex. Received: October 29, 1997 / Accepted: November 27, 1997     

连续血液净化治疗先天性代谢缺陷病重症有机酸血症

目的　分析、评价连续血液净化 (continuousbloodpurification ,CBP)对先天性代谢缺陷病 (inbornerrorsofmetabolism ,IEM )重症有机酸血症的治疗效果 ,探讨其治疗机制。方法　用BaxterBM 2 5机对 9例IEM重症有机酸血症患儿行CBP治疗 ,对比治疗前后血气、生化值 ,并比较症状、体征改善情况。结果　 9例患儿入院时 pH值 (6 87± 0 2 5 )、BB(1 6± 0 0 8)mmol/L、SB(4 0± 0 5 8)mmol/L、BE(- 2 6 1± 2 80 )mmol/L、乳酸 (15 2± 3 6 4 )mmol/L ,血氨 (2 87 5 3± 132 4 3) μmol/L ,呈重度代谢性酸中毒。经 1～ 2次 ,9～ 32hCBP治疗 ,患儿症状、体征好转 ,酸碱平衡部分纠正 ,pH(7 33± 0 18)mmol/L、BB(18 0± 2 5 6 )mmol/L、SB(19 1± 2 2 5 )mmol/L、BE(- 3 4± 1 6 2 )mmol/L、乳酸 (3 1±0 5 5 )mmol/L ,血氨 (39 2 1± 2 2 85 ) μmol/L ,较治疗前显著好转。 结论　临床观察提示 ,CBP是治疗IEM有机酸血症的一种快速有效的方法     

Diagnostic yield from routine metabolic screening tests in evaluation of global developmental delay and intellectual disability

Global developmental delay and intellectual disability (GDD/ID) affect 3% of the paediatric population. Although inborn errors of metabolism (IEM) are not a common cause of GDD/ID, early therapeutic intervention can improve neurodevelopmental manifestations. In 2012, a first-tier test panel, including specialized metabolic and routine chemistry tests, was piloted to community-based paediatricians in British Columbia with aims to achieve earlier diagnosis of treatable IEM.ObjectiveThe aim of this retrospective review was to evaluate the diagnostic yield from these first-tier tests in the 7 years before (2006 to 2012) and after (2013 to 2019) implementation at the community paediatrician level.ResultsPrior and postimplementation diagnostic yield of an IEM from first-tier metabolic testing was 9 out of 986 (0.91%) and 11 out of 4,345 children (0.25%), respectively. Disorders of creatine metabolism and organic acidurias were the most frequently established diagnoses in both time periods. No diagnoses were established through acylcarnitine copper/ceruloplasmin, lactate, or ammonia testing. Twenty out of 24 patients had specific neurological or other red flag signs in addition to GDD/ID. Four boys diagnosed with an x-linked creatine transporter defect (CTD) had speech-language delay as the most prominent finding.ConclusionsThe expansion of first-tier metabolic testing to community-based paediatricians in BC did not yield an increase in IEM diagnoses. A modified first-tier test panel should be offered to patients with GDD/ID, neurologic, and/or red flag signs. Urine creatine testing in boys with speech-language delay warrants consideration to detect CTD.     

Stem Cell Through Present and Future

Stem cell transplantation (SCT) has the potential to transform the lives of children with a wide variety of genetic diseases, ranging from inherent defects of hemopoietic cell production or function through to metabolic diseases mostly affecting solid organs. For these children life expectancy or quality of life would otherwise be very poor.1 It ranks as one of the most remarkable therapeutic advances of the past 40 years. Despite rapid technological improvements, however, there are still many short term risks and potential long term toxicities. Consequently, the rapid emergence of alternative therapies (including new drugs, enzyme and gene therapies), necessitate constant re-evaluation of the risk/benefit ratio for each disease and hence the appropriateness of SCT. This review describes the major aspects of the transplant process, indications for transplantation, outcome statistics, and areas where alternative therapies are becoming available. SCT remains a highly experimental therapy. Due to the relatively short history of the discipline no data exists on truly long term follow up. This is important as some organs benefit relatively poorly or problems may emerge which were never apparent as part of the untreated disease. The speed of technological change makes randomised trials on these diseases, which are individually quite rare, almost impossible to perform.     

Impact of inborn errors of metabolism on admission and mortality in a pediatric intensive care unit

The authors conducted a retrospective analysis of the patients admitted to a pediatric intensive care unit (PICU) during a five-year period, with specific focus on those with a suspected or confirmed diagnosis of inborn errors of metabolism (IEM), in order to ascertain the resources required to care for these patients. Medical records were reviewed for all admissions between January 1998 and December 2002 in a single metabolic referral center, and a subset of patients were identified with suspected IEM at admission or diagnosed IEM at hospital discharge. These patient charts were then further reviewed and the following information was extracted: IEM diagnosis, demographic data, biochemical characteristics at admission, need for mechanical ventilation, use of extracorporeal removal therapy, and outcome at PICU discharge. The study population comprised 70 patients (2.2% of all admissions during the study period) and included 33 neonates and 37 children aged >28 days. IEM diagnosis was known at the time of admission to the PICU in 9/33 of the neonates and 23/37 of the older children. Forty-three of the patients required invasive mechanical ventilation, while continuous extracorporeal removal therapy was used in 27 children. The median length of PICU stay was 3 days (range, 1 to 13 days) and 20 patients (28.6%) died. In conclusion, these observations show that inherited metabolic disease may be as frequent a primary diagnosis as septic shock in some PICUs. In neonates, these diseases are not usually diagnosed prior to PICU admission. Patients with IEM admitted to a PICU require aggressive support (including mechanical ventilation and extracorporeal removal therapies), and consume significant resources for relatively short PICU stays. These patients constitute a significant diagnostic and therapeutic challenge for pediatric intensivists.     

CONTINUOUS ARTERIOVENOUS HEMODIAFILTRATION IN THE ACUTE TREATMENT OF HYPERAMMONAEMIA DUE TO ORNITHINE TRANSCARBAMYLASE DEFICIENCY

Background. Acute hyperammonemia caused by urea cycle disorder is a medical emergency for which immediate managements should be taken to minimize permanent brain damage. Among different enzyme defects, ornithine transcarbamylase deficiency (OTC) is one of the most common enzyme defect in urea cycle disorders. We utilized continuous renal replacement therapy techniques in the acute treatment of hyperammonemia due to ornithine transcarbamylase deficiency.

Patients and methods. Three male neonates with elevated serum ammonia levels were shown, based on urine organic acid analysis and serum amino acid studies, to have OTC deficiency. Administration of sodium benzoate and sodium phenylacetate for activating alternative nitrogen waste pathway were used associated with protein restriction. Other modalities, including blood exchange transfusion, peritoneal dialysis, continuous renal replacement therapy were utilized in an attempt to lower serum ammonia concentration.

Results. We report the successful use of continuous arteriovenous hemofiltration (CAVH), continuous arteriovenous hemodialysis (CAVHD), continuous arteriovenous hemodiafiltration (CAVHDF) in the acute management of hyperammonemia due to OTC deficiency. We also compared the ammonia clearance between peritoneal dialysis, exchange transfusion, CAVH, CAVHD and CAVHDF. It demonstrated the evidence that CAVHDF provides the best ammonia clearance.

Conclusion. Continuous renal replacement therapy including CAVH, CAVHD, and CAVHDF may be the alternative techniques for acute management of hyperammonemia in inborn error of metabolism when dialysis machine is not available. Our data suggests CAVHDF provides the best ammonia clearance.     

Hepatocyte transplantation program: Lessons learned and future strategies

This review aims to share the lessons we learned over time during the setting of the hepatocyte transplantation(HT) program at the Hepatic Cell Therapy Unit at Hospital La Fe in Valencia. New sources of liver tissue for hepatocyte isolation have been explored. The hepatocyte isolation and cryopreservation procedures have been optimized and quality criteria for assessment of functionality of hepatocyte preparations and suitability for HT have been established. The results indicate that:(1) Only highly viable and functional hepatocytes allow to recover those functions lacking in the native liver;(2) Organs with steatosis(≥ 40%) and from elderly donors are declined since low hepatocyte yields, viability and cell survival after cryopreservation, are obtained;(3) Neonatal hepatocytes are cryopreserved without significant loss of viability or function representing high-quality cells to improve human HT;(4) Cryopreservation has the advantage of providing hepatocytes constantly available and of allowing the quality evaluation and suitability for transplantation; and(5) Our results from 5 adults with acute liver failure and 4 from children with inborn metabolic diseases, indicate that HT could be a veryuseful and safe cell therapy, as long as viable and metabolically functional human hepatocytes are used.     

Vaccination in children with inborn errors of metabolism

Inborn errors of metabolism (IEMs) are a large group of very heterogeneous diseases, and the impact of the available vaccines on children with IEMs may vary depending on the child's metabolic characteristics. The main aim of this review is to re-analyse the administration of vaccines to such children in the light of the most recent data. As a whole, these indicate that children with stable or slowly progressing IEMs can receive the recommended schedules of all of the recommended vaccinations. However, vaccines should be administered more cautiously to children with IEMs associated with a significant risk of morbidity and/or mortality with catabolic events: i.e. under strict medical supervision, and only when the children are clinically well and their metabolic condition is acceptably controlled. Furthermore, a number of IEMs have been associated with immune deficiency although, in most cases, the immunological abnormalities disappear or are significantly reduced when the metabolic defect is corrected. The response to vaccines is therefore unpredictable, but it is reasonable to think that it may be inadequate in children with the most severe immune defects. In addition to defective protection, vaccines administered to children with IEM and severe immunodeficiency can actually cause the disease they were meant to prevent. This explains why experts suggest that vaccines based on live attenuated viruses should not be given to such children, although all of the other vaccines can be administered without limitation regardless of the type of immune defect. Nevertheless, only specific multicentre studies will make it possible to say when and how to use vaccines in children with different types of IEM in order to protect them from vaccine-preventable diseases without any risk of worsening their metabolic situation.     

Inborn Errors of Immunity: how to diagnose them?

ObjectivesInborn Errors of Immunity are characterized by infectious conditions and manifestations of immune dysregulation. The diversity of clinical phenotypes can make it difficult to direct the laboratory investigation. This article aims to update the investigation of immunological competence in the context of primary defects of the immune system.Source of dataSearches were carried out on Pubmed to review articles published in the last five years, in English, French or Spanish, using the terms “diagnosis” OR “investigation” AND “immunodeficiency” or “primary immunodeficiency” or “inborn errors of immunity” NOT “HIV”. Recent textbook editions have also been consulted.Summary of findingsThe immune system competence investigation should be started based on clinical phenotypes. Relevant data are: characterization of infectious conditions (location, recurrence, types of infectious agents, response to treatment), age during symptom onset and associated manifestations (growth impairment, allergy, autoimmunity, malignancies, fever and signs of inflammation without the identification of infection or autoimmunity) and family history. These data contribute to the selection of tests to be performed.ConclusionsThe diagnostic investigation of Inborn Errors of Immunity should be guided by the clinical characterization of patients, aiming to optimize the use of complementary tests. Many diagnoses are attained only through genetic tests, which are not always available. However, the absence of a diagnosis of certainty should never delay the implementation of therapeutic measures that preserve patient life and health.