Fatty acid oxidation disorders: outcome and long-term prognosis

Long-term major clinical outcomes in patients with long chain fatty acid oxidation disorders before and after transition to triheptanoin treatment--A retrospective chart review

BACKGROUND

Long chain fatty acid oxidation disorders (LC-FAODs) are caused by defects in the metabolic pathway that converts stored long-chain fatty acids into energy, leading to a deficiency in mitochondrial energy production during times of physiologic stress and fasting. Severe and potentially life threatening clinical manifestations include rhabdomyolysis, hypoglycemia, hypotonia/weakness, cardiomyopathy and sudden death. We present the largest cohort of patients to date treated with triheptanoin, a specialized medium odd chain (C7) triglyceride, as a novel energy source for the treatment of LC-FAOD.

METHODS

This was a retrospective, comprehensive medical record review study of data from 20 of a total 24 patients with LC-FAOD who were treated for up to 12.5 years with triheptanoin, as part of a compassionate use protocol. Clinical outcomes including hospitalization event rates, number of hospitalization days/year, and abnormal laboratory values were determined for the total period of the study before and after triheptanoin treatment, as well as for specified periods before and after initiation of triheptanoin treatment. Other events of interest were documented including rhabdomyolysis, hypoglycemia, and cardiomyopathy.

RESULTS

LC-FAOD in these 20 subjects was associated with 320 hospitalizations from birth to the end date of study. The mean hospitalization days/year decreased significantly by 67% during the period after triheptanoin initiation (n=15; 5.76 vs 17.55 vs; P=0.0242) and a trend toward a 35% lower hospitalization event rate was observed in the period after triheptanoin initiation compared with the before-treatment period (n=16 subjects >6 months of age; 1.26 vs 1.94; P=0.1126). The hypoglycemia event rate per year in 9 subjects with hypoglycemia problems declined significantly by 96% (0.04 vs 0.92; P=0.0091) and related hospitalization days/year were also significantly reduced (n=9; 0.18 vs 8.42; P=0.0257). The rhabdomyolysis hospital event rate in 11 affected subjects was similar before and after treatment but the number of hospitalization days/year trended lower in the period after triheptanoin initiation (n=9; 2.36 vs 5.94; P=0.1224) and peak CK levels trended toward a 68% decrease from 85,855 to 27,597 units in 7 subjects with reported peak CK values before and after treatment (P=0.1279). Triheptanoin was generally well tolerated. Gastrointestinal symptoms were the most commonly reported side effects.

CONCLUSIONS

This retrospective study represents the largest analysis reported to date of treatment of LC-FAOD with triheptanoin. The data suggest that triheptanoin improves the course of disease by decreasing the incidence and duration of major clinical manifestations and should be the focus of prospective investigations. Significant heterogeneity in the routine clinical care provided to subjects during the periods studied and the natural variation of clinical course of LC-FAODs with time emphasize the need of additional study of the use of triheptanoin.

A semiquantitative metric for evaluating clinical actionability of incidental or secondary findings from genome-scale sequencing

PURPOSE

As genome-scale sequencing is increasingly applied in clinical scenarios, a wide variety of genomic findings will be discovered as secondary or incidental findings, and there is debate about how they should be handled. The clinical actionability of such findings varies, necessitating standardized frameworks for a priori decision making about their analysis.

METHODS

We established a semiquantitative metric to assess five elements of actionability: severity and likelihood of the disease outcome, efficacy and burden of intervention, and knowledge base, with a total score from 0 to 15.

RESULTS

The semiquantitative metric was applied to a list of putative actionable conditions, the list of genes recommended by the American College of Medical Genetics and Genomics (ACMG) for return when deleterious variants are discovered as secondary/incidental findings, and a random sample of 1,000 genes. Scores from the list of putative actionable conditions (median = 12) and the ACMG list (median = 11) were both statistically different than the randomly selected genes (median = 7) (P < 0.0001, two-tailed Mann-Whitney test).

CONCLUSION

Gene-disease pairs having a score of 11 or higher represent the top quintile of actionability. The semiquantitative metric effectively assesses clinical actionability, promotes transparency, and may facilitate assessments of clinical actionability by various groups and in diverse contexts.Genet Med 18 5, 467-475.

Medium-chain acyl-CoA dehydrogenase deficiency associated with a novel splice mutation in the ACADM gene missed by newborn screening

Background

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most common disorder of mitochondrial fatty acid β-oxidation and a target disease of newborn screening in many countries.

Case presentation

We report on two siblings with mild MCAD deficiency associated with a novel splice site mutation in the ACADM gene. The younger sibling was detected by newborn screening, while the older sister was missed, but diagnosed later on by genetic family testing. Both children were found to be compound heterozygous for the common c.985A > G (p.K329E) mutation and a novel splice site mutation, c.600-18G > A, in the ACADM gene. To determine the biological consequence of the c.600-18G > A mutation putative missplicing was investigated at RNA level in granulocytes and monocytes of one of the patients. The splice site mutation was shown to lead to partial missplicing of the ACADM pre-mRNA. Of three detected transcripts two result in truncated, non-functional MCAD proteins as reflected by the reduced octanoyl-CoA oxidation rate in both patients. In one patient a decrease of the octanoyl-CoA oxidation rate was found during a febrile infection indicating that missplicing may be temperature-sensitive.

Conclusions

Our data indicate that the c.600-18G > A variant activates a cryptic splice site, which competes with the natural splice site. Due to only partial missplicing sufficient functional MCAD protein remains to result in mild MCADD that may be missed by newborn screening.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0199-5) contains supplementary material, which is available to authorized users.

Uncoupling, metabolic inhibition and induction of mitochondrial permeability transition in rat liver mitochondria caused by the major long-chain hydroxyl monocarboxylic fatty acids accumulating in LCHAD deficiency

Patients with long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiency commonly present liver dysfunction whose pathogenesis is unknown. We studied the effects of long-chain 3-hydroxylated fatty acids (LCHFA) that accumulate in LCHAD deficiency on liver bioenergetics using mitochondrial preparations from young rats. We provide strong evidence that 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, the monocarboxylic acids that are found at the highest tissue concentrations in this disorder, act as metabolic inhibitors and uncouplers of oxidative phosphorylation. These conclusions are based on the findings that these fatty acids decreased ADP-stimulated (state 3) and uncoupled respiration, mitochondrial membrane potential and NAD(P)H content, and, in contrast, increased resting (state 4) respiration. We also verified that 3HTA and 3HPA markedly reduced Ca2+ retention capacity and induced swelling in Ca2+-loaded mitochondria. These effects were mediated by mitochondrial permeability transition (MPT) induction since they were totally prevented by the classical MPT inhibitors cyclosporin A and ADP, as well as by ruthenium red, a Ca2+ uptake blocker. Taken together, our data demonstrate that the major monocarboxylic LCHFA accumulating in LCHAD deficiency disrupt energy mitochondrial homeostasis in the liver. It is proposed that this pathomechanism may explain at least in part the hepatic alterations characteristic of the affected patients.

Rhabdomyolysis in a neonate due to very long chain acyl CoA dehydrogenase deficiency

Very long chain acyl CoA dehydrogenase deficiency (VLCADD) is an inborn error in long chain fatty acid oxidation with significant variability in the severity and timing of its clinical presentation. Neonatal presentations of VLCADD have included hypoglycemia and cardiomyopathy while rhabdomyolysis is usually a later onset complication. We describe a neonate with VLCADD presenting with rhabdomyolysis prior to the return of an abnormal newborn screen. This report suggests that evaluating for rhabdomyolysis, in addition to a cardiac and hepatic work-up, is an important part of the initial evaluation of an infant with an abnormal newborn screen suggesting a diagnosis of VLCADD.

Rare diseases in clinical endocrinology: a taxonomic classification system

PURPOSE

Rare endocrine-metabolic diseases (REMD) represent an important area in the field of medicine and pharmacology. The rare diseases of interest to endocrinologists involve all fields of endocrinology, including rare diseases of the pituitary, thyroid and adrenal glands, paraganglia, ovary and testis, disorders of bone and mineral metabolism, energy and lipid metabolism, water metabolism, and syndromes with possible involvement of multiple endocrine glands, and neuroendocrine tumors. Taking advantage of the constitution of a study group on REMD within the Italian Society of Endocrinology, consisting of basic and clinical scientists, a document on the taxonomy of REMD has been produced.

METHODS AND RESULTS

This document has been designed to include mainly REMD manifesting or persisting into adulthood. The taxonomy of REMD of the adult comprises a total of 166 main disorders, 338 including all variants and subtypes, described into 11 tables.

CONCLUSIONS

This report provides a complete taxonomy to classify REMD of the adult. In the future, the creation of registries of rare endocrine diseases to collect data on cohorts of patients and the development of common and standardized diagnostic and therapeutic pathways for each rare endocrine disease is advisable. This will help planning and performing intervention studies in larger groups of patients to prove the efficacy, effectiveness, and safety of a specific treatment.

Kruppel-like factors in muscle health and disease

Kruppel-like factors (KLF) are zinc-finger DNA-binding transcription factors that are critical regulators of tissue homeostasis. Emerging evidence suggests that KLFs are critical regulators of muscle biology in the context of cardiovascular health and disease. The focus of this review is to provide an overview of the current state of knowledge regarding the physiologic and pathologic roles of KLFs in the three lineages of muscle: cardiac, smooth, and skeletal.

Resuscitation of a neonate with medium chain acyl-coenzyme a dehydrogenase deficiency using extracorporeal life support

We report a neonate with medium chain acyl-coenzyme A dehydrogenase deficiency (MCAD) who had a cardiac arrest due to ventricular tachycardia and fibrillation. Extracorporeal life support (ECLS) was deployed, from which the baby was subsequently separated and discharged from hospital. This case was a rare neonatal presentation of MCAD and an uncommon indication for ECLS. We discuss the presentations of patients with MCAD and the use of ECLS for patients with possible inborn errors of metabolism and other unknown primary diagnoses.

Stable isotope dilution liquid chromatography/mass spectrometry analysis of cellular and tissue medium- and long-chain acyl-coenzyme A thioesters

RATIONALE

Acyl-Coenzyme A (CoA) thioesters are the principal form of activated carboxylates in cells and tissues. They are employed as acyl carriers that facilitate the transfer of acyl groups to lipids and proteins. Quantification of medium- and long-chain acyl-CoAs represents a significant bioanalytical challenge because of their instability.

METHODS

Stable isotope dilution liquid chromatography/selected reaction monitoring-mass spectrometry (LC/SRM-MS) provides the most specific and sensitive method for the analysis of CoA species. However, relevant heavy isotope standards are not available and they are challenging to prepare by chemical synthesis. Stable isotope labeling by essential nutrients in cell culture (SILEC), developed originally for the preparation of stable isotope labeled short-chain acyl-CoA thioester standards, has now been extended to medium-chain and long-chain acyl-CoAs and used for LC/SRM-MS analyses.

RESULTS

Customized SILEC standards with >98% isotopic purity were prepared using mouse Hepa 1c1c7 cells cultured in pantothenic-free media fortified with [(13) C3 (15) N1 ]-pantothenic acid and selected fatty acids. A SILEC standard in combination with LC/SRM-MS was employed to quantify cellular concentrations of arachidonoyl-CoA (a representative long-chain acyl-CoA) in two human colon cancer cell lines. A panel of SILEC standards was also employed in combination LC/SRM-MS to quantify medium- and long-chain acyl-CoAs in mouse liver.

CONCLUSIONS

This new SILEC-based method in combination with LC/SRM-MS will make it possible to rigorously quantify medium- and long-chain acyl-CoAs in cells and tissues. The method will facilitate studies of medium- and long-chain acyl-CoA dehydrogenase deficiencies as well as studies on the role of medium- and long-chain acyl-CoAs in cellular metabolism.

A case of an infant suffered from a fatal scald injury - validity and limitations of postmortem CT imaging

A 9months-old infant has died of scald burn by the hot water from the fallen electric pot at home. Postmortem computed tomography (CT) scanning prior to autopsy contributed to exclude the possibilities of old and new bone fractures or hidden massive hemorrhages. This procedure helped the pathologists to avoid dissecting all the extremities, which is time-consuming, laborious and often hurtful to the innocent parents of the deceased. On the other hand it did not successfully show the distribution of the scald burn injury on the skin, which reminded us of the importance of external examination even when the whole-body CT is performed. The manner of death was considered to be accident since the cause of death was burn shock and there was no significant evidence suggesting child abuse. Scene investigation and reproductive experiment have revealed that there was a structural problem in the lid of the pot, which comes off very easily in a certain condition. In order to prevent a similar accident, report of the case to the manufacturer is essential for the improvement of the apparatus. This case, however, has been remained to be unreported because of the confidentiality of the investigative information in judicial autopsy. Finally, we recommend a partial revision of the reporting system in Japan to prevent the recurrence of such tragic accidents.

Birth Prevalence of Fatty Acid β-Oxidation Disorders in Iberia

Mitochondrial fatty acid β-oxidation disorders (FAOD) are main targets for newborn screening (NBS) programs, which are excellent data sources for accurate estimations of disease birth prevalence. Epidemiological data is of key importance for the understanding of the natural history of the disorders as well as to define more effective public health strategies. In order to estimate FAOD birth prevalence in Iberia, the authors collected data from six NBS programs from Portugal and Spain, encompassing the screening of more than 1.6 million newborns by tandem mass spectrometry (MS/MS), and compared it with available data from other populations. The participating NBS programs are responsible for the screening of about 46% of all Iberian newborns. Data reveals that Iberia has one of the highest FAOD prevalence in Europe (1:7,914) and that Portugal has the highest birth prevalence of FAOD reported so far (1:6,351), strongly influenced by the high prevalence of medium-chain acyl-CoA dehydrogenase deficiency (MCADD; 1:8,380), one of the highest ever reported. This is justified by the fact that more than 90% of Portuguese MCADD patients are of Gypsy origin, a community characterized by a high degree of consanguinity. From the comparative analysis of various populations with comparable data other differences emerge, which points to the existence of significant variations in FAOD prevalences among different populations, but without any clear European variation pattern. Considering that FAOD are one of the justifications for MS/MS NBS, the now estimated birth prevalences stress the need to screen all Iberian newborns for this group of inherited metabolic disorders.

Mitochondrial bioenergetics deregulation caused by long-chain 3-hydroxy fatty acids accumulating in LCHAD and MTP deficiencies in rat brain: a possible role of mPTP opening as a pathomechanism in these disorders?

Long-chain 3-hydroxylated fatty acids (LCHFA) accumulate in long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies. Affected patients usually present severe neonatal symptoms involving cardiac and hepatic functions, although long-term neurological abnormalities are also commonly observed. Since the underlying mechanisms of brain damage are practically unknown and have not been properly investigated, we studied the effects of LCHFA on important parameters of mitochondrial homeostasis in isolated mitochondria from cerebral cortex of developing rats. 3-Hydroxytetradecanoic acid (3 HTA) reduced mitochondrial membrane potential, NAD(P)H levels, Ca(2+) retention capacity and ATP content, besides inducing swelling, cytochrome c release and H2O2 production in Ca(2+)-loaded mitochondrial preparations. We also found that cyclosporine A plus ADP, as well as ruthenium red, a Ca(2+) uptake blocker, prevented these effects, suggesting the involvement of the mitochondrial permeability transition pore (mPTP) and an important role for Ca(2+), respectively. 3-Hydroxydodecanoic and 3-hydroxypalmitic acids, that also accumulate in LCHAD and MTP deficiencies, similarly induced mitochondrial swelling and decreased ATP content, but to a variable degree pending on the size of their carbon chain. It is proposed that mPTP opening induced by LCHFA disrupts brain bioenergetics and may contribute at least partly to explain the neurologic dysfunction observed in patients affected by LCHAD and MTP deficiencies.

From genome to phenome-Simple inborn errors of metabolism as complex traits

Sporadically, patients with a proven defect in either mFAO or OXPHOS are described presenting with a metabolic profile and clinical phenotype expressing concurrent defects in both pathways. Biochemical linkages between both processes are tight. Therefore, it is striking that concurrent dysfunction of both systems occurs so infrequent. In this review, the linkages between OXPHOS and mFAO and the hypothesized processes responsible for concurrent problems in both systems are reviewed, both from the point of view of primary biochemical connections and secondary cellular responses, i.e. signaling pathways constituting nutrient-sensing networks. We propose that affected signaling pathways may play an important role in the phenomenon of concurrent defects. Recent data indicate that interference in the affected signaling pathways may resolve the pathological phenotype even though the primary enzyme deficiency persists. This offers new (unexpected) prospects for treatment of these inborn errors of metabolism. This article is part of a Special Issue entitled: From Genome to Function.

Prolonged QTc interval in association with medium-chain acyl-coenzyme A dehydrogenase deficiency

Medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency is the most common disorder of mitochondrial fatty acid oxidation. We report a term male infant who presented at 3 days of age with hypoglycemia, compensated metabolic acidosis, hypocalcemia, and prolonged QTc interval. Pregnancy was complicated by maternal premature atrial contractions and premature ventricular contractions. Prolongation of the QTc interval resolved after correction of metabolic derangements. The newborn screen was suggestive for MCAD deficiency, a diagnosis that was confirmed on genetic analysis that showed homozygosity for the disease-associated missense A985G mutation in the ACADM gene. This is the first report of acquired prolonged QTc in a neonate with MCAD deficiency, and it suggests that MCAD deficiency should be considered in the differential diagnoses of acute neonatal illnesses associated with electrocardiographic abnormality. We review the clinical presentation and diagnosis of MCAD deficiency in neonates.

Infants suspected to have very-long chain acyl-CoA dehydrogenase deficiency from newborn screening

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a fatty acid oxidation disorder with widely varying presentations that has presented a significant challenge to newborn screening (NBS). The Western States Regional Genetics Services Collaborative developed a workgroup to study infants with NBS positive for VLCADD. We performed retrospective analysis of newborns with elevated C14:1-acylcarnitine on NBS in California, Oregon, Washington, and Hawai'i including available confirmatory testing and clinical information. Overall, from 2,802,504 children screened, there were 242 cases screen-positive for VLCADD. There were 34 symptomatic true positive cases, 18 asymptomatic true positives, 112 false positives, 55 heterozygotes, 11 lost to follow-up, and 12 other disorders. One in 11,581 newborns had an abnormal NBS for suspected VLCADD. Comparison of analytes and analyte ratios from the NBS demonstrated statistically significant differences between true positive and false positive groups for C14:1, C14, C14:1/C2, and C14:1/C16. The positive predictive value for all true positive cases was 94%, 54%, and 23% when C14:1 was ≥2.0 μM, ≥1.0 μM, and ≥0.7 μM, respectively. Sequential post-analytical analysis could reduce the referral rate in 25.8% of cases. This study is the largest reported follow-up of infants with NBS screen-positive results for suspected VLCADD and demonstrates the necessity of developing comprehensive and consistent long-term follow-up NBS systems. Application of clinical information revealed differences between symptomatic and asymptomatic children with VLCADD. Comparison of NBS analytes and analyte ratios may be valuable in developing more effective diagnostic algorithms.

Performance of serum and dried blood spot acylcarnitine profiles for detection of fatty acid β-oxidation disorders in adult patients with rhabdomyolysis

BACKGROUND

Plasma/serum and dried blood spot (DBS) acylcarnitine profiles (ACPs) are key to the diagnosis of mitochondrial fatty acid β-oxidation disorders (FAODs). Despite their significant clinical applications, limited published data exists to compare their sensitivities and specificities. We retrospectively evaluated these two methods in adult patients with a history of rhabdomyolysis; investigated for an underlying FAOD.

METHODS

A retrospective study was completed for adult patients (investigated between 2003 and 2011) meeting the inclusion criteria of a history of recurrent rhabdomyolysis or one episode of rhabdomyolysis with a history of exercise intolerance. All subjects underwent investigations for an underlying FAOD including DBS and serum ACP analysis concurrently collected during a symptom-free period, and skin biopsy for cultured fibroblast fatty acid oxidation studies or enzyme activity measurement, as indicated, with or without molecular confirmation. Their medical records were reviewed, and the performance of the two methods were compared.

RESULTS

Seven out of 31 subjects (22.6 %) were diagnosed with an underlying FAOD. Long chain acylcarnitines were more markedly elevated in serum samples from confirmed CPTII cases (n = 4) as compared to matched DBS profiles. The sensitivity and specificity of DBS ACP was 71.4 % (95 % CI, 0.30-0.95) and 100 % (95 % CI, 0.79-1.00), respectively, compared to a sensitivity of 100 % (95 % CI, 0.56-1.00) and a specificity of 94.7 % (95 % CI, 0.72-1.00) for serum ACP.

CONCLUSION

FAODs appear to be a common cause of recurrent rhabdomyolysis or rhabdomyolysis with a history of exercise induced myalgia. At least historically, FAODs maybe underdiagnosed in adults with rhabdomyolysis. This study suggests that serum ACP might be more sensitive than DBS ACP for detection of an underlying FAOD in adults with rhabdomyolysis while asymptomatic.

Clinical and biological features at diagnosis in mitochondrial fatty acid beta-oxidation defects: a French pediatric study of 187 patients

INTRODUCTION

Mitochondrial fatty acid β-oxidation defects (FAODs) are a group of severe inherited metabolic diseases, most of which can be treated with favorable prognosis following diagnosis. A description of the broad range of phenotypes resulting from these defects remains incomplete, and for this study, we sought to investigate the semiology at diagnosis in a country without a newborn screening program for FAODs.

METHODS

Using a retrospective French multicentre study, we analyzed 187 children aged <6 years at diagnosis with FAOD confirmed by enzymatic and/or molecular analyses. Clinical and biological parameters at diagnosis were assessed to screen liver, heart, neurological, and muscle symptoms. Information concerning the long-term prognosis was also collected.

RESULTS

Predominant hepatic symptoms were observed in 89 % of patients regardless of the underlying defect. The most frequent symptoms observed were hepatomegaly (92 %), increased blood alanine aminotransferase (ALAT) level (82 %), and steatosis (88 %). Other frequent features included Reye syndrome (49 %), increased gamma-glutamyltranspeptidase (GGT) (37 %), and liver failure (27 %). Extrahepatic features were often associated in the foreground. Hypoglycemia (75 %), neurological (64 %), muscle (61 %), or cardiac features (55 %) [as either cardiomyopathy (47 %) or arrhythmias (31 %)] were frequently documented. Hemodynamic events (41 %) were represented by shock (31 %) or sudden death (35 %). Hyperammonemia (73 %) and hyperlactacidemia (57 %) were the two main biochemical features. Total, very-long-chain acyl-CoA dehydrogenase (VLCADD), long-chain 3-hydroxyacylCoA dehydrogenase (LCHADD), and medium-chain acyl-CoA dehydrogenase (MCADD) deficiency mortality rates were 48 %, 60 %, 63 %, and 20 % respectively.

CONCLUSION

This study presents clinical features of a large cohort of patients with FAODs in a country without neonatal screening for FAODs. Our results highlight liver as the main organ involved at diagnosis regardless of age at diagnosis, classical phenotype (i.e., cardiac, hepatic, or muscular), or enzyme deficiency. Although steatosis may be observed in various inherited metabolic defects, it is a reliable indicator of FAOD and should prompt systematic screening when the diagnosis is suspected. The poor long-term prognoses reported are a strong argument for inclusion of FAODs in newborn screening programs.

Newborn screening for medium-chain acyl-CoA dehydrogenase deficiency: regional experience and high incidence of carnitine deficiency

Background

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most common inherited defect in the mitochondrial fatty acid oxidation pathway, resulting in significant morbidity and mortality in undiagnosed patients.

Newborn screening (NBS) has considerably improved MCADD outcome, but the risk of complication remains in some patients. The aim of this study was to evaluate the relationship between genotype, biochemical parameters and clinical data at diagnosis and during follow-up, in order to optimize monitoring of these patients.

Methods

We carried out a multicenter study in southwest Europe, of MCADD patients detected by NBS. Evaluated NBS data included free carnitine (C0) and the acylcarnitines C8, C10, C10:1 together with C8/C2 and C8/C10 ratios, clinical presentation parameters and genotype, in 45 patients. Follow-up data included C0 levels, duration of carnitine supplementation and occurrence of metabolic crises.

Results

C8/C2 ratio and C8 were the most accurate biomarkers of MCADD in NBS. We found a high number of patients homozygous for the prevalent c.985A > G mutation (75%). Moreover, in these patients C8, C8/C10 and C8/C2 were higher than in patients with other genotypes, while median value of C0 was significantly lower (23 μmol/L vs 36 μmol/L).

The average follow-up period was 43 months. To keep carnitine levels within the normal range, carnitine supplementation was required in 82% of patients, and for a longer period in patients homozygotes for the c.985A>G mutation than in patients with other genotypes (average 31 vs 18 months). Even with treatment, median C0 levels remained lower in homozygous patients than in those with other genotypes (14 μmol/L vs 22 μmol/L).

Two patients died and another three suffered a metabolic crisis, all of whom were homozygous for the c.985 A>G mutation.

Conclusions

Our data show a direct association between homozygosity for c.985A>G and lower carnitine values at diagnosis, and a higher dose of carnitine supplementation for maintenance within the normal range. This study contributes to a better understanding of the relationship between genotype and phenotype in newborn patients with MCADD detected through screening which could be useful in improving follow-up strategies and clinical outcome.

Regulation of mitochondrial fatty acid β-oxidation in human: what can we learn from inborn fatty acid β-oxidation deficiencies?

The mitochondrial fatty acid β-oxidation (FAO) pathway plays a crucial role in ATP production in many tissues with high-energy demand. This is highlighted by the diverse and possibly severe clinical manifestations of inborn fatty acid β-oxidation deficiencies. More than fifteen genetic FAO enzyme defects have been described to date, forming a large group of rare diseases. Inborn FAO disorders are characterized by a high genetic heterogeneity, with a variety of gene mutations resulting in complete or partial loss-of-function of the corresponding enzyme. The panel of observed phenotypes varies from multi-organ failure in the neonate with fatal outcome, up to milder late onset manifestations associated with significant disabilities. Diagnosis of FAO disorders has markedly improved over the last decades, but few treatments are available. The clinical, biochemical, and molecular analysis of these disorders provided new, and sometimes unexpected, data on the organization and regulation of mitochondrial FAO in humans, in various tissues, and at various stages of development. This will be illustrated by examples of FAO defects affecting enzymes of long-chain fatty acid import into the mitochondria, or Lynen helix enzymes. The involvement of the transcriptional network regulating FAO gene expression, in particular the PGC-1α/PPAR axis, as a target for pharmacological therapy of these genetic disorders, will also be discussed.

Molecular and cellular pathology of very-long-chain acyl-CoA dehydrogenase deficiency

BACKGROUND

Very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency (VLCADD) is diagnosed in the US through newborn screening (NBS). NBS often unequivocally identifies affected individuals, but a growing number of variant patterns can represent mild disease or heterozygous carriers.

AIMS

To evaluate the validity of standard diagnostic procedures for VLCADD by using functional in vitro tools.

METHODS

We retrospectively investigated 13 patient samples referred to our laboratory because of a suspicion of VLCADD but with some uncertainty to the diagnosis. All 13 patients were suspected of having VLCADD either because of abnormal NBS or suggestive clinical findings. ACADVL genomic DNA sequencing data were available for twelve of them. Ten of the patients had an abnormal NBS suggestive of VLCADD, with three samples showing equivocal results. Three exhibited suggestive clinical findings and blood acylcarnitine profile (two of them had a normal NBS and the third one was unscreened). Assay of VLCAD activity and immunoblotting or immunohistologic staining for VLCAD were performed on fibroblasts. Prokaryotic mutagenesis and expression studies were performed for nine uncharacterized ACADVL missense mutations.

RESULTS

VLCAD activity was abnormal in fibroblast cells from 9 patients (8 identified through abnormal NBS, 1 through clinical symptoms). For these 9 patients, immunoblotting/staining showed the variable presence of VLCAD; all but one had two mutated alleles. Two patients with equivocal NBS results (and a heterozygous genotype) and the two patients with normal NBS exhibited normal VLCAD activity and normal VLCAD protein on immunoblotting/staining thus ruling out VLCAD deficiency. Nine pathogenic missense mutations were characterized with prokaryotic expression studies and showed a decrease in enzyme activity and variable stability of VLCAD antigen.

CONCLUSIONS

These results emphasize the importance of functional investigation of abnormal NBS or clinical testing suggestive but not diagnostic of VLCADD. A larger prospective study is necessary to better define the clinical and metabolic ramifications of the defects identified in such patients.

Metabolic and mitochondrial effects of antiretroviral drug exposure in pregnancy and postpartum: implications for fetal and future health

Antiretroviral drugs (ARVs) are indispensable in the treatment and prevention of human immunodeficiency virus infection. Although their use before, during and after pregnancy is considered safe for mother and child, there are still lingering concerns about their long-term health consequences and the ramifications of their effects on lipid, glucose, intermediary and mitochondrial metabolism. This article reviews the known effects of ARVs on macromolecular and mitochondrial metabolism as well as the potential maternal, fetal, neonatal and adult health risks associated with abnormal energy metabolism during gestation. Recommendations about enhanced monitoring for these risks in affected populations are being provided.

Abnormal newborn screens and acylcarnitines in HIV-exposed and ARV-exposed infants

BACKGROUND

Antiretroviral drugs (ARV), specifically nucleoside analogs, are toxic to mitochondrial oxidative phosphorylation. Other metabolic pathways, such as fatty acid oxidation, organic acid metabolism and amino acid metabolism, are dependent on normal oxidative phosphorylation but remain unexamined as potential points of ARV toxicity.

METHODS

We analyzed newborn screening data from New York and compared proportions of abnormal newborn metabolic screens in HIV antibody screen-positive and HIV screen-negative neonates. Subsequently, we compared acylcarnitine levels in ARV-exposed (n = 16) and ARV-unexposed (n = 14) HIV-exposed infants to assess for dysfunctional fatty and organic acid metabolism.

RESULTS

: The rate of abnormal newborn metabolic screens in HIV screen-positive infants was higher than that in the general population (2.2% versus 1.2%; P = 0.00025), most of which were for disorders of mitochondria-related metabolism. Abnormal acylcarnitine levels occurred more frequently in ARV-exposed compared with ARV-unexposed infants (43% versus 0%; P = 0.02).

CONCLUSIONS

A higher proportion of positive metabolic screens in HIV screen-positive neonates suggests that HIV or ARV exposure is associated with dysfunctional intermediary metabolism in newborns. Abnormal acylcarnitine levels were more frequent in ARV-exposed infants, suggesting that ARV may perturb normal fatty acid oxidation in some infants. Studies designed to validate and determine the clinical significance of these findings are warranted.

Stoffwechselerkrankungen

Entsprechend ihrer Wanderung bei isoelektrischer Fokussierung werden die allelen Varianten des α1-AT als Proteinaseinhibitorphänotypen (Pi) klassifiziert. Die dominierende Isoform ist der normale Phänotyp M, daneben gibt es die Mangelvarianten S und Z sowie eine 0-Variante.

Achieving the "triple aim" for inborn errors of metabolism: a review of challenges to outcomes research and presentation of a new practice-based evidence framework

Across all areas of health care, decision makers are in pursuit of what Berwick and colleagues have called the “triple aim”: improving patient experiences with care, improving health outcomes, and managing health system impacts. This is challenging in a rare disease context, as exemplified by inborn errors of metabolism. There is a need for evaluative outcomes research to support effective and appropriate care for inborn errors of metabolism. We suggest that such research should consider interventions at both the level of the health system (e.g., early detection through newborn screening, programs to provide access to treatments) and the level of individual patient care (e.g., orphan drugs, medical foods). We have developed a practice-based evidence framework to guide outcomes research for inborn errors of metabolism. Focusing on outcomes across the triple aim, this framework integrates three priority themes: tailoring care in the context of clinical heterogeneity; a shift from “urgent care” to “opportunity for improvement”; and the need to evaluate the comparative effectiveness of emerging and established therapies. Guided by the framework, a new Canadian research network has been established to generate knowledge that will inform the design and delivery of health services for patients with inborn errors of metabolism and other rare diseases.

Genet Med 2013:15(6):415–422

Molecular diagnosis for a fatal case of very long-chain acyl-CoA dehydrogenase deficiency in Hong Kong Chinese with a novel mutation: a preventable death by newborn screening

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is one of the most common fatty acid oxidation defects that cause sudden unexpected deaths in infants. The death attributed to VLCAD deficiency can be prevented by early diagnosis with expanded newborn screening using tandem mass spectrometry. A favorable outcome can be achieved with early diagnosis and prompt treatment. However, such newborn screening has not yet been available in Hong Kong. We report a 2-month-old boy who succumbed 5 hours after admission with the diagnosis of VLCAD deficiency confirmed by genetic analysis performed after death. The patient was compound heterozygous for a novel splicing mutation ACADVL NM_000018.2:c.277+2T>G; NC_000017.10:g.7123997T>G and a known disease-causing mutation ACADVL NM_000018.2:c.388_390del; NP_000009.1: p.Glu130del. Family screening was performed for at-risk siblings. The rapid downhill course of the patient clearly illustrates the need of newborn screening for early diagnosis. Our patient was asymptomatic before metabolic decompensation. However, once metabolic decompensation occurred, rapid deterioration and death followed, which obviated the opportunity to diagnose and treat. The only way to save these patients' lives and improve their outcome is early diagnosis and appropriate treatment. Therefore, we strongly urge the implementation of newborn screening using tandem mass spectrometry for VLCAD deficiency and other highly treatable inborn errors of metabolism in Hong Kong.

Ablation of steroid receptor coactivator-3 resembles the human CACT metabolic myopathy

Oxidation of lipid substrates is essential for survival in fasting and other catabolic conditions, sparing glucose for the brain and other glucose-dependent tissues. Here we show Steroid Receptor Coactivator-3 (SRC-3) plays a central role in long chain fatty acid metabolism by directly regulating carnitine/acyl-carnitine translocase (CACT) gene expression. Genetic deficiency of CACT in humans is accompanied by a constellation of metabolic and toxicity phenotypes including hypoketonemia, hypoglycemia, hyperammonemia, and impaired neurologic, cardiac and skeletal muscle performance, each of which is apparent in mice lacking SRC-3 expression. Consistent with human cases of CACT deficiency, dietary rescue with short chain fatty acids drastically attenuates the clinical hallmarks of the disease in mice devoid of SRC-3. Collectively, our results position SRC-3 as a key regulator of β-oxidation. Moreover, these findings allow us to consider platform coactivators such as the SRCs as potential contributors to syndromes such as CACT deficiency, previously considered as monogenic.

Disruption of redox homeostasis in cerebral cortex of developing rats by acylcarnitines accumulating in medium-chain acyl-CoA dehydrogenase deficiency

Medium-chain fatty acids and acylcarnitines accumulate in medium-chain acyl-CoA dehydrogenase deficiency (MCADD), the most frequent fatty acid oxidation defect clinically characterized by episodic crises with vomiting, seizures and coma. Considering that the pathophysiology of the neurological symptoms observed in MCADD is poorly known and, to our knowledge, there is no report on the involvement of acylcarnitines in the brain damage presented by the affected patients, the objective of the present study was to investigate the in vitro effects of hexanoylcarnitine (HC), octanoylcarnitine, decanoylcarnitine (DC) and cis-4-decenoylcarnitine (cDC) at concentrations varying from 0.01 to 1.0mM on important oxidative stress parameters in cerebral cortex of young rats. HC, DC and cDC significantly induced lipid peroxidation, as determined by increased thiobarbituric acid-reactive substances (TBA-RS) values. In addition, carbonyl formation was significantly augmented and sulfhydryl content diminished by DC, reflecting induction of protein oxidative damage. HC, DC and cDC also decreased glutathione (GSH) levels, the most important brain antioxidant defense. Furthermore, DC-induced elevation of TBA-RS values and decrease of GSH levels were prevented by the free radical scavengers melatonin and α-tocopherol, indicating the involvement of reactive oxygen species in these effects. We also found that l-carnitine itself did not induce lipid and protein oxidative damage, neither reduced the antioxidant defenses. Our present data show that the major medium-chain acylcarnitines accumulating in MCADD elicit oxidative stress in rat brain. It is therefore presumed that these compounds may be involved to a certain extent in the pathogenesis of the neurologic dysfunction of MCADD.

Long-term correction of very long-chain acyl-coA dehydrogenase deficiency in mice using AAV9 gene therapy

Very long-chain acyl-coA dehydrogenase (VLCAD) is the rate-limiting step in mitochondrial fatty acid oxidation. VLCAD-deficient mice and patients clinical symptoms stem from not only an energy deficiency but also long-chain metabolite accumulations. VLCAD-deficient mice were treated systemically with 1 × 10¹² vector genomes of recombinant adeno-associated virus 9 (rAAV9)-VLCAD. Biochemical correction was observed in vector-treated mice beginning 2 weeks postinjection, as characterized by a significant drop in long-chain fatty acyl accumulates in whole blood after an overnight fast. Changes persisted through the termination point around 20 weeks postinjection. Magnetic resonance spectroscopy (MRS) and tandem mass spectrometry (MS/MS) revealed normalization of intramuscular lipids in treated animals. Correction was not observed in liver tissue extracts, but cardiac muscle extracts showed significant reduction of long-chain metabolites. Disease-specific phenotypes were characterized, including thermoregulation and maintenance of euglycemia after a fasting cold challenge. Internal body temperatures of untreated VLCAD^−/− mice dropped below 20 °C and the mice became lethargic, requiring euthanasia. In contrast, all rAAV9-treated VLCAD^−/− mice and the wild-type controls maintained body temperatures. rAAV9-treated VLCAD^−/− mice maintained euglycemia, whereas untreated VLCAD^−/− mice suffered hypoglycemia following a fasting cold challenge. These promising results suggest rAAV9 gene therapy as a potential treatment for VLCAD deficiency in humans.

Lethal Undiagnosed Very Long-Chain Acyl-CoA Dehydrogenase Deficiency with Mild C14-Acylcarnitine Abnormalities on Newborn Screening

Newborn screening identifies patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency with disease-specific acylcarnitine profiles. We here present a patient who died at 16 months during a gastrointestinal infection because of undiagnosed VLCADD. The primary acylcarnitine profile on newborn screening performed at 55 h of life revealed C14-acylcarnitine values and ratios within the 1st percentile VLCAD disease range and C12-acylcarnitine values and ratios within the 10th percentile disease range. The acylcarnitine cumulative percentiles in neonatal dried blood spots analyzed by tandem mass spectrometry have been obtained by participants of the Region 4 Stork collaborative project. A secondary screen was requested by the screening laboratory as a result of the initial screen and was normal on day 8 of life. With the initial acylcarnitines only within the 1st-10th percentile disease range, newborn screening for VLCAD deficiency was in the end considered normal. The most important lesson learned is that acylcarnitine profiles from healthy newborns during catabolism and VLCAD-deficient patients can in certain cases not be distinguished by any means. With a known high incidence of false positive cases for VLCADD on newborn screening, it finally remains unknown, whether forced anabolism in the first days of life may result in normal acylcarnitine profiles in VLCAD-deficient patients resulting in missed cases and false negatives on newborn screening. Our observations are of great significance since they demonstrate the limitations of acylcarnitine analysis as screening tool for VLCAD-deficiency.

Expanded newborn screening: articulating the ontology of diseases with bridging work in the clinic

Population screening follows the logic of secondary prevention: a population is screened to detect disease early and to initiate treatment before symptoms emerge. However, not all population screening is justifiable under all circumstances. In this article, we unpack Wilson and Jungner's requirement that knowledge about the natural history of a disease must be 'adequate' for screening to proceed. We argue that any prior understanding of disease is inevitably found to be insufficient once population screening is instituted. Drawing upon ethnographic observations of clinical consultations and staff meetings conducted in a California regional clinical centre for metabolic-genetic disorders, we introduce the notion of bridging work to draw attention to the collective activities of the genetics team to revise the ontological nature of conditions unsettled by population-based newborn screening. Bridging work refers to the many activities required to reconcile the promise of technologies with the realities of their implementation. We illustrate how clinicians bridge the gap between what was known about a disease prior to screening and anomalous screening results, leading to an ontological transformation of disease categories.

Extended newborn screening: an update for the general paediatrician

Extended newborn screening (ENBS) with the use of tandem mass spectrometry technology is well established in all Australian states and in New Zealand. ENBS has afforded a marked reduction in morbidity and mortality in select conditions such as medium-chain acyl-CoA dehydrogenase deficiency. While this technology has been of great benefit to newborn screening, it comes with many inherent and unforeseen challenges. In this review, we discuss the successes and challenges associated with ENBS.

[Medium-chain acyl-CoA-dehydrogenase (MCAD) deficiency: French consensus for neonatal screening, diagnosis, and management]

MCAD deficiency is the most common fatty acid oxidation disorder, with the prevalence varying from 1/10,000 to 1/27,000 in the countries adjacent to France. As the High Authority for Health has recently proposed including MCAD deficiency in the panel of diseases neonatally screened for in France, a consensus was written for the management of MCAD deficiency diagnosed either clinically or by neonatal screening. Patients may present acutely with hyperammonemia, hypoglycemia, encephalopathy, and hepatomegaly, mainly after a prolonged fast of intercurrent infection. Sudden death related to heartbeat disorders may also occur. The diagnosis of MCAD deficiency is suspected on the plasma acylcarnitine and/or the urinary organic acid profile. The diagnosis is confirmed by molecular biology and the enzymatic activity for patients who are not homozygous for the main mutation c.985A>G. However, some MCAD-deficient individuals may remain asymptomatic throughout life. The mainstay of treatment consists in avoiding prolonged fast and prescribing l-carnitine for patients who exhibit a deficiency in plasma carnitine. This management has radically modified the natural history of MCAD deficiency. This consensus will allow homogeneous management of these patients once the neonatal screening of MCAD deficiency has been introduced in France.

Variability in the clinical management of fatty acid oxidation disorders: results of a survey of Canadian metabolic physicians

INTRODUCTION

There is little robust empirical evidence on which to base treatment recommendations for fatty acid oxidation disorders. While consensus guidelines are important, understanding areas where there is a lack of consensus is also critical to inform priorities for future evaluative research.

METHODS

We surveyed Canadian metabolic physicians on the treatment of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, and mitochondrial trifunctional protein (MTP) deficiency. We ascertained physicians' opinions on the use of different interventions for the long-term management of patients as well as for the management of acute illness, focusing on identifying interventions characterized by high variability in opinions. We also investigated factors influencing treatment decisions.

RESULTS

We received 18 responses (response rate 45%). Participants focused on avoidance of fasting and increased meal frequency as interventions for the management of MCAD deficiency. For the long-chain disorders, avoidance of fasting remained the most consistently endorsed intervention, with additional highly endorsed treatments differing for VLCAD versus LCHAD/MTP deficiency. L-carnitine supplementation and restriction of dietary fat were characterized by high variability in physicians' opinions, as were several interventions specific to long-chain disorders. Social factors and patient characteristics were important influences on treatment decisions.

CONCLUSIONS

Based on our findings we suggest that high priority treatments for rigorous effectiveness studies could include L-carnitine supplementation (MCAD and LCHAD/MTP deficiencies), restriction of dietary fat, and, for the long-chain disorders, feeding practices for breastfed infants and the use of various supplements (essential fatty acids, carbohydrates, cornstarch, multivitamins).

Propionic acidemia: neonatal versus selective metabolic screening

BACKGROUND

Whereas propionic acidemia (PA) is a target disease of newborn screening (NBS) in many countries, it is not in others. Data on the benefit of NBS for PA are sparse.

STUDY DESIGN

Twenty PA patients diagnosed through NBS were compared to 35 patients diagnosed by selective metabolic screening (SMS) prompted by clinical findings, family history, or routine laboratory test results. Clinical and biochemical data of patients from 16 metabolic centers in Germany, Austria, and Switzerland were evaluated retrospectively. Additionally, assessment of the intelligent quotient (IQ) was performed. In a second step, the number of PA patients who have died within the past 20 years was estimated based on information provided by the participating metabolic centers.

RESULTS

Patients diagnosed through NBS had neither a milder clinical course regarding the number of metabolic crises nor a better neurological outcome. Among NBS patients, 63% were already symptomatic at the time of diagnosis, and <10% of all patients remained asymptomatic. Among all PA patients, 76% were found to be at least mildly mentally retarded, with an IQ <69. IQ was negatively correlated with the number of metabolic decompensations, but not simply with the patients' age. Physical development was also impaired in the majority of patients. Mortality rates tended to be lower in NBS patients compared with patients diagnosed by SMS.

CONCLUSION

Early diagnosis of PA through NBS seems to be associated with a lower mortality rate. However, no significant benefit could be shown for surviving patients with regard to their clinical course, including the number of metabolic crises, physical and neurocognitive development, and long-term complications.

Newborn screening for medium chain acyl-CoA dehydrogenase deficiency in England: prevalence, predictive value and test validity based on 1.5 million screened babies

BACKGROUND

Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is a rare, life-threatening condition. Early diagnosis by screening asymptomatic newborns may improve outcome, but the benefit to newborns identified with variants not encountered clinically is uncertain.

OBJECTIVE

To estimate, overall and by ethnic group: screen-positive prevalence and predictive value (PPV); MCADD prevalence; proportion MCADD variants detected of predicted definite or uncertain clinical importance.

SETTING

All births in areas of high ethnic minority prevalence in England.

METHODS

Prospective multicentre pilot screening service; testing at age five to eight days; standardized screening, diagnostic and management protocols; independent expert review of screen-positive cases to assign MCADD diagnosis and predicted clinical importance (definite or uncertain).

RESULTS

Approximately 1.5 million babies (79% white; 10% Asian) were screened. MCADD was confirmed in 147 of 190 babies with a positive screening result (screen-positive prevalence: 1.20 per 10,000; MCADD prevalence: 0.94 per 10,000; PPV 77% [95% CI 71-83]), comprising 103 (70%) with MCADD variants of definite clinical importance (95 white [95%]; 2 Asian [2%]) and 44 (30%) with variants of uncertain clinical importance (29 white [67%]; 12 Asian [28%]).

CONCLUSION

One baby in every 10,000 born in England is diagnosed with MCADD by newborn screening; around 60 babies each year. While the majority of MCADD variants detected are predicted to be of definite clinical importance, this varies according to ethnic group, with variants of uncertain importance most commonly found in Asian babies. These findings provide support for MCADD screening but highlight the need to take account of the ethnic diversity of the population tested at implementation.

Metabolic myopathies: clinical features and diagnostic approach

The rheumatologist is frequently called on to evaluate patients with complaints of myalgia, muscle cramps, and fatigue. The evaluation of these patients presents a diagnostic challenge given the nonspecific and intermittent nature of their complaints, often leading to inappropriate diagnostic testing. When these symptoms are associated with physical exertion, a metabolic myopathy should be suspected Although inflammatory myopathies may present with similar features, such a pattern should prompt a thorough evaluation for an underlying metabolic myopathy. This review discusses the most common causes of metabolic myopathies and reviews the current diagnostic options available to the clinician.

Data mining methods for classification of Medium-Chain Acyl-CoA dehydrogenase deficiency (MCADD) using non-derivatized tandem MS neonatal screening data

Newborn screening programs for severe metabolic disorders using tandem mass spectrometry are widely used. Medium-Chain Acyl-CoA dehydrogenase deficiency (MCADD) is the most prevalent mitochondrial fatty acid oxidation defect (1:15,000 newborns) and it has been proven that early detection of this metabolic disease decreases mortality and improves the outcome. In previous studies, data mining methods on derivatized tandem MS datasets have shown high classification accuracies. However, no machine learning methods currently have been applied to datasets based on non-derivatized screening methods. A dataset with 44,159 blood samples was collected using a non-derivatized screening method as part of a systematic newborn screening by the PCMA screening center (Belgium). Twelve MCADD cases were present in this partially MCADD-enriched dataset. We extended three data mining methods, namely C4.5 decision trees, logistic regression and ridge logistic regression, with a parameter and threshold optimization method and evaluated their applicability as a diagnostic support tool. Within a stratified cross-validation setting, a grid search was performed for each model for a wide range of model parameters, included variables and classification thresholds. The best performing model used ridge logistic regression and achieved a sensitivity of 100%, a specificity of 99.987% and a positive predictive value of 32% (recalibrated for a real population), obtained in a stratified cross-validation setting. These results were further validated on an independent test set. Using a method that combines ridge logistic regression with variable selection and threshold optimization, a significantly improved performance was achieved compared to the current state-of-the-art for derivatized data, while retaining more interpretability and requiring less variables. The results indicate the potential value of data mining methods as a diagnostic support tool.

The first three years of screening for medium chain acyl-CoA dehydrogenase deficiency (MCADD) by newborn screening ontario

Background

Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is a disorder of mitochondrial fatty acid oxidation and is one of the most common inborn errors of metabolism. Identification of MCADD via newborn screening permits the introduction of interventions that can significantly reduce associated morbidity and mortality. This study reports on the first three years of newborn screening for MCADD in Ontario, Canada.

Methods

Newborn Screening Ontario began screening for MCADD in April 2006, by quantification of acylcarnitines (primarily octanoylcarnitine, C8) in dried blood spots using tandem mass spectrometry. Babies with positive screening results were referred to physicians at one of five regional Newborn Screening Treatment Centres, who were responsible for diagnostic evaluation and follow-up care.

Results

From April 2006 through March 2009, approximately 439 000 infants were screened for MCADD in Ontario. Seventy-four infants screened positive, with a median C8 level of 0.68 uM (range 0.33-30.41 uM). Thirty-one of the screen positive infants have been confirmed to have MCADD, while 36 have been confirmed to be unaffected. Screening C8 levels were higher among infants with MCADD (median 8.93 uM) compared to those with false positive results (median 0.47 uM). Molecular testing was available for 29 confirmed cases of MCADD, 15 of whom were homozygous for the common c.985A > G mutation. Infants homozygous for the common mutation tended to have higher C8 levels (median 12.13 uM) relative to compound heterozygotes for c.985A > G and a second detectable mutation (median 2.01 uM). Eight confirmed mutation carriers were identified among infants in the false positive group. The positive predictive value of a screen positive for MCADD was 46%. The estimated birth prevalence of MCADD in Ontario is approximately 1 in 14 000.

Conclusions

The birth prevalence of MCADD and positive predictive value of the screening test were similar to those identified by other newborn screening programs internationally. We observed some evidence of correlation between genotype and biochemical phenotype (C8 levels), and between C8 screening levels and eventual diagnosis. Current research priorities include further examining the relationships among genotype, biochemical phenotype, and clinical phenotype, with the ultimate goal of improving clinical risk prediction in order to provide tailored disease management advice and genetic counselling to families.

Expanded newborn screening: reducing harm, assessing benefit

Achieving the goals of newborn screening is, as for any screening, a balancing act: getting the maximum benefit from screening while producing the minimum harm. The advent of "expanded" newborn screening, with a large number of disorders detectable using a single test, has also posed problems, not new, but now more obvious. One is the finding of many more cases by screening, the extra cases being largely patients who have attenuated phenotypes and may remain asymptomatic for many years, even throughout life. These may or may not require active management in the short term, but do need lifelong awareness. Additionally, disorders have been included that are now thought benign or largely so. Babies risk being unnecessarily medicalized. Assessing outcome has also proved difficult because of the rarity of some disorders and the impracticality of randomized controlled trials. The requirements for valid studies include the need for case definitions, comparable comparison groups and probably assessment on a whole-population basis. An Australia-wide study of tandem mass spectrometry newborn screening involving 2 million screened and unscreened babies has demonstrated benefits overall to screened patients at age 6 years. The study was too small to provide conclusions for individual disorders other than for medium-chain acyl-CoA dehydrogenase deficiency.