Medium-chain acyl-CoA dehydrogenase deficiency: sudden and unexpected death of a 45 year old woman

Causes of Sudden Unexpected Death in Childhood: Autopsy Findings from a Specialist Centre

OBJECTIVES

To investigate the aetiologies of sudden unexpected death from natural causes in children aged 1-18 years by retrospective examination of autopsy records from a single centre.

MATERIALS AND METHODS

The post-mortem findings from 548 children (1996-2015) were examined. Details were entered into an established research database and categorized according to >400 pre-defined criteria.

RESULTS

There were 265 previously apparently healthy children and 283 with pre-existing, potentially life-limiting, conditions. There were more males than females (M:F 1.4:1), and deaths were more frequent in the winter. Infection was commonest accounting for 43% of all deaths. Non-infectious diseases were identified as cause of death in 28%, and 29% of all deaths were unexplained. There was no significant difference in the proportions of deaths in each category between the previously healthy children and those with pre-existing conditions.

CONCLUSION

Sudden unexpected death is a rare presentation of death in childhood and those with pre-existing conditions may be more at risk. Standardisation of the post-mortem procedure in such cases may result in more ancillary investigations performed as routine and may reduce the number of cases that are 'unexplained'.

Management Principles for Acute Illness in Patients With Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency

Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is a fatty acid oxidation disorder in which the patient is unable to break down fats to produce energy. This disorder places children at risk for metabolic decompensation during periods of stress, such as routine childhood illnesses. The intent of this clinical report is to provide pediatricians with additional information regarding the acute clinical care of patients with MCADD. Although each patient with MCADD will still be expected to have a primary metabolic physician, the involvement of the primary care provider is crucial as well. Appropriate treatment of children with MCADD can lead to avoidance of morbidity and mortality.

Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature

Background Short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency is a rare inborn error of metabolism with uncertain clinical significance. As it leads to C5-carnitine (i.e. isovalerylcarnitine, 2methylbutyrilcarnitine, or pivaloylcarnitine) elevation, SBCAD deficiency is detectable at newborn screening, requiring differential diagnosis from isovaleric acidemia and pivalic acid administration. Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency. Methods We report two cases of SBCAD deficiency and provide a review of the available literature on this condition. Results Two siblings newly diagnosed with SBCAD deficiency are reported. Newborn screening allowed the early diagnosis in the second-born (C5=0.5 μmol/L, normal 0.05-0.3 μmol/L) and addressed selective screening in the 5-year asymptomatic brother (C5=1.9 μmol/L). Both patients showed increased urinary excretion of 2MBG and two mutations in the ACADSB gene (c.443C>T/c.1145C>T). Currently, both the patients are asymptomatic. Longitudinal biochemical monitoring of the two patients while on treatment with carnitine (100 mg/kg/day) was provided. Based on our experience and the literature review (162 patients), SBCAD deficiency is symptomatic in about 10% of reported patients. Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive. On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop. Acute metabolic decompensation due to catabolic stressors can occur, as observed in one newly reported patient. Fifteen mutations in the ACADSB gene are known, including the newly identified variant c.1145C>T (p.Thr382Met), variably associated to the phenotype. In the Hmong population, SBCAD deficiency is highly prevalent, mostly due to the founder mutation c.1165A>G, and is largely asymptomatic. Conclusions Although mostly asymptomatic, considering SBCAD deficiency as a non-disease in non-Hmong subjects appears unsafe. Catabolic situations can precipitate acute metabolic decompensation. Carnitine supplementation and valproate avoidance appear to be indicated. Providing an emergency protocol for the management of acute catabolic episodes seems reasonable in asymptomatic patients with SBCAD deficiency. Longitudinal follow-up is recommended.

cis-4-Decenoic and decanoic acids impair mitochondrial energy, redox and Ca(2+) homeostasis and induce mitochondrial permeability transition pore opening in rat brain and liver: Possible implications for the pathogenesis of MCAD deficiency

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is biochemically characterized by tissue accumulation of octanoic (OA), decanoic (DA) and cis-4-decenoic (cDA) acids, as well as by their carnitine by-products. Untreated patients present episodic encephalopathic crises and biochemical liver alterations, whose pathophysiology is poorly known. We investigated the effects of OA, DA, cDA, octanoylcarnitine (OC) and decanoylcarnitine (DC) on critical mitochondrial functions in rat brain and liver. DA and cDA increased resting respiration and diminished ADP- and CCCP-stimulated respiration and complexes II-III and IV activities in both tissues. The data indicate that these compounds behave as uncouplers and metabolic inhibitors of oxidative phosphorylation. Noteworthy, metabolic inhibition was more evident in brain as compared to liver. DA and cDA also markedly decreased mitochondrial membrane potential, NAD(P)H content and Ca(2+) retention capacity in Ca(2+)-loaded brain and liver mitochondria. The reduction of Ca(2+) retention capacity was more pronounced in liver and totally prevented by cyclosporine A and ADP, as well as by ruthenium red, demonstrating the involvement of mitochondrial permeability transition (mPT) and Ca(2+). Furthermore, cDA induced lipid peroxidation in brain and liver mitochondria and increased hydrogen peroxide formation in brain, suggesting the participation of oxidative damage in cDA-induced alterations. Interestingly, OA, OC and DC did not alter the evaluated parameters, implying lower toxicity for these compounds. Our results suggest that DA and cDA, in contrast to OA and medium-chain acylcarnitines, disturb important mitochondrial functions in brain and liver by multiple mechanisms that are possibly involved in the neuropathology and liver alterations observed in MCAD deficiency.

Mitochondrial dysfunction in fatty acid oxidation disorders: insights from human and animal studies

Patients affected by FAOD commonly present with hepatopathy, cardiomyopathy, skeletal myopathy and encephalopathy. Human and animal evidences indicate that mitochondrial functions are disrupted by fatty acids and derivatives accumulating in these disorders, suggesting that lipotoxicity may contribute to their pathogenesis.

Mitochondrial fatty acid oxidation (FAO) plays a pivotal role in maintaining body energy homoeostasis mainly during catabolic states. Oxidation of fatty acids requires approximately 25 proteins. Inherited defects of FAO have been identified in the majority of these proteins and constitute an important group of inborn errors of metabolism. Affected patients usually present with severe hepatopathy, cardiomyopathy and skeletal myopathy, whereas some patients may suffer acute and/or progressive encephalopathy whose pathogenesis is poorly known. In recent years growing evidence has emerged indicating that energy deficiency/disruption of mitochondrial homoeostasis is involved in the pathophysiology of some fatty acid oxidation defects (FAOD), although the exact underlying mechanisms are not yet established. Characteristic fatty acids and carnitine derivatives are found at high concentrations in these patients and more markedly during episodes of metabolic decompensation that are associated with worsening of clinical symptoms. Therefore, it is conceivable that these compounds may be toxic. We will briefly summarize the current knowledge obtained from patients and genetic mouse models with these disorders indicating that disruption of mitochondrial energy, redox and calcium homoeostasis is involved in the pathophysiology of the tissue damage in the more common FAOD, including medium-chain acyl-CoA dehydrogenase (MCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies. We will also provide evidence that the fatty acids and derivatives that accumulate in these diseases disrupt mitochondrial homoeostasis. The elucidation of the toxic mechanisms of these compounds may offer new perspectives for potential novel adjuvant therapeutic strategies in selected disorders of this group.

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.

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.

[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.

Toxicity of octanoate and decanoate in rat peripheral tissues: evidence of bioenergetic dysfunction and oxidative damage induction in liver and skeletal muscle

The accumulation of octanoic (OA) and decanoic (DA) acids in tissue is the common finding in medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD), the most frequent defect of fatty acid oxidation. Affected patients present hypoketotic hypoglycemia, rhabdomyolysis, hepatomegaly, seizures and lethargy, which may progress to coma and death. At present, the pathophysiological mechanisms underlying hepatic and skeletal muscle alterations in affected patients are poorly known. Therefore, in the present work, we investigated the in vitro effects of OA and DA, the accumulating metabolites in MCADD, on various bioenergetics and oxidative stress parameters. It was verified that OA and DA decreased complexes I-III, II-III and IV activities in liver and also inhibit complex IV activity in skeletal muscle. In addition, DA decreased complexes II-III activity in skeletal muscle. We also verified that OA and DA increased TBA-RS levels and carbonyl content in both tissues. Finally, DA, but not OA, significantly decreased GSH levels in rat skeletal muscle. Our present data show that the medium-chain fatty acids that accumulate in MCADD impair electron transfer through respiratory chain and elicit oxidative damage in rat liver and skeletal muscle. It may be therefore presumed that these mechanisms are involved in the pathophysiology of the hepatopathy and rhabdomyolysis presented by MCADD-affected patients.

Maternal medium-chain acyl-CoA dehydrogenase deficiency identified by newborn screening

Prior to the advent of expanded newborn screening, sudden and unexplained death was often the first and only symptom of medium-chain acyl-CoA dehydrogenase deficiency (MCADD). With the use of tandem mass spectrometry, infants can now be identified and treated before a life threatening metabolic decompensation occurs. Newborn screening has also been shown to detect previously undiagnosed maternal inborn errors of metabolism. We have now diagnosed two women with MCADD following the identification of low free carnitine in their newborns. While one of the women reported prior symptoms of fasting intolerance, neither had a history of metabolic decompensation or other symptoms consistent with a fatty acid oxidation disorder. These cases illustrate the importance of including urine organic acid analysis and an acylcarnitine profile as part of the confirmatory testing algorithm for mothers when low free carnitine is identified in their infants.

The clinical manifestation of MCAD deficiency: challenges towards adulthood in the screened population

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most common fatty acid oxidation disorder. Typically, undiagnosed individuals are asymptomatic until an episode of increased energy demand and fasting occurs, resulting in metabolic derangement. Phenotypic heterogeneity has been increasingly realized, with reports of both neonates and adults manifesting with life-threatening symptoms including encephalopathy, rhabdomyolysis, and cardiac failure. If diagnosed presymptomatically, outcome is favorable basically by avoidance of fasting. Early detection by newborn screening (NBS) has significantly reduced the incidence of severe adverse events including deaths. In this manuscript we focus on the natural course of the disease in both children and adults. Although NBS for MCADD has been successfully established, continuing efforts need to be made to avoid acute crises and deterioration of outcome in screened patients entering adolescence and adulthood.

Sudden death in medium chain acyl-coenzyme a dehydrogenase deficiency (MCADD) despite newborn screening

INTRODUCTION

Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is the most frequent of the fatty acid oxidation disorders (FAOD), a group caused by defects in the mitochondrial B-oxidation of fatty acids. Fatty acid oxidation is critical in supplying energy during periods when glucose is limited or when energy needs are increased beyond the availability of glucose. In MCADD, this energy shortage can result in acute metabolic episodes or sudden death. The prevention of sudden death from MCADD served as the primary impetus to expand newborn screening. However, we have experienced sudden death in four children with MCADD despite their detection by newborn screening. The purpose of this report is to alert others to the danger of sudden death in MCADD even when it is detected by newborn screening, to identify the clinical symptoms that precede sudden death, and to examine the relationship between the newborn screening result and the risk for sudden death.

METHODS

We describe these children and their metabolic findings with emphasis on their newborn screening octanoylcarnitine (C8) level, the primary marker for newborn detection of MCADD. We also performed a literature search of cases of sudden death in MCADD in which the clinical status preceding death is described.

RESULTS

The newborn screening C8 levels in our four cases were markedly elevated, ranging from 8.4 to 24.8micromol/L (cut off<0.8micromol/L). Only two of the children were homozygous for the common c.985A>G MCAD mutation; the other two were heterozygous for this mutation. Similarly, among the eight reported cases which included MCAD genotypes, five were homozygous for the c.985A>G mutation, while two were heterozygous and one was homozygous for a splice site mutation. Vomiting 12-24h before sudden death was present in all four of our cases, and the review of reported cases of sudden death in MCADD disclosed vomiting as a frequent symptom.

CONCLUSION

We suggest that in MCADD (1) a newborn screening C8 level of 6micromol/L or greater represents particular risk of sudden death; (2) that MCAD genotypes other than homozygosity for the c.985A>G mutation are also associated with sudden death; (3) that vomiting is a frequent symptom preceding sudden death; and (4) social support and medical follow-up of these families are crucial in reducing the occurrence of sudden death.

Maternal systemic primary carnitine deficiency uncovered by newborn screening: clinical, biochemical, and molecular aspects

BACKGROUND

Systemic primary carnitine deficiency is an autosomal recessive disorder of the carnitine cycle caused by mutations in the SLC22A5 gene that encodes the carnitine transporter, organic cation transporter. Systemic primary carnitine deficiency typically presents in childhood with either metabolic decompensation or cardiomyopathy. We report five families in which low free carnitine levels in the infants' newborn screening have led to the diagnosis of maternal systemic primary carnitine deficiency.

METHODS

Blood samples from the infants and /or their family members were used to extract the DNA. The entire coding regions of the SLC22A5 gene were sequenced. The clinical data were obtained from the referring metabolic specialists.

RESULT

Sequencing the SLC22A5 gene allowed molecular confirmation with identification of three novel mutations: c.1195C>T (p.R399W), c.1324_1325GC>AT (p.A442I), and c.43G>T (p.G15W). All infants were asymptomatic at the time of diagnosis, and one was found to have systemic primary carnitine deficiency. Three mothers are asymptomatic, one had decreased stamina during pregnancy, and one has mild fatigability and developed preeclampsia.

DISCUSSION

These findings provide further evidence that systemic primary carnitine deficiency presents with a broad clinical spectrum from a metabolic decompensation in infancy to an asymptomatic adult. The maternal systemic primary carnitine deficiency was uncovered by the newborn screening results supporting the previous notion that newborn screening can identify some of the maternal inborn errors of metabolism. It also emphasizes the importance of maternal evaluation after identification of a low free carnitine level in the newborn screening.

A neonatal death due to medium-chain acyl-CoA dehydrogenase deficiency: utilization of the neonatal metabolic screen in a functional approach to sudden unexplained infant death

We report a perinatal death due to medium-chain acyl-CoA dehydrogenase deficiency, which was referred to the Coroner's Physician as sudden unexplained infant death. Detailed death investigation including the autopsy findings, and newborn biochemical and molecular studies revealed the cause and natural manner of death. This disorder affects fatty acid oxidation and results in decreased tolerance for fasting, which can be life threatening. This case illustrates the critical role of newborn screening in the investigation of perinatal death. A brief historical perspective of the origins of newborn biochemical screening is also presented.

Adult presentations of medium-chain acyl-CoA dehydrogenase deficiency (MCADD)

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is an autosomal recessive disorder of mitochondrial fatty acid oxidation which is usually diagnosed in infancy or through neonatal screening. In the absence of population screening, adults with undiagnosed MCADD can be expected. This review discusses 14 cases that were identified during adulthood. The mortality of infantile patients is approximately 25% whereas in this adult case series it was shown it to be 50% in acutely presenting patients and 29% in total. Therefore, undiagnosed individuals are at risk of sudden fatal metabolic decompensation with high mortality. This review illustrates the need to consider the possibility of a fatty acid oxidation defect in an adult who presents with unexplained sudden clinical deterioration, particularly if precipitated by fasting or alcohol consumption. A history of unexplained sibling death may also raise the index of suspicion. There also needs to be appropriate clinical support for those patients identified clinically or as a result of family studies (sibling or parent).

Evidence that the major metabolites accumulating in medium-chain acyl-CoA dehydrogenase deficiency disturb mitochondrial energy homeostasis in rat brain

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is an inherited metabolic disorder of fatty acid oxidation in which the affected patients predominantly present high levels of octanoic (OA) and decanoic (DA) acids and their glycine and carnitine by-products in tissues and body fluids. It is clinically characterized by episodic encephalopathic crises with coma and seizures, as well as by progressive neurological involvement, whose pathophysiology is poorly known. In the present work, we investigated the in vitro effects of OA and DA on various parameters of energy homeostasis in mitochondrial preparations from brain of young rats. We found that OA and DA markedly increased state 4 respiration and diminished state 3 respiration as well as the respiratory control ratio, the mitochondrial membrane potential and the matrix NAD(P)H levels. In addition, DA-elicited increase in oxygen consumption in state 4 respiration was partially prevented by atractyloside, indicating the involvement of the adenine nucleotide translocator. OA and DA also reduced ADP/O ratio, CCCP-stimulated respiration and the activities of respiratory chain complexes. The data indicate that the major accumulating fatty acids in MCADD act as uncouplers of oxidative phosphorylation and as metabolic inhibitors. Furthermore, DA, but not OA, provoked a marked mitochondrial swelling and cytochrome c release from mitochondria, reflecting a permeabilization of the inner mitochondrial membrane. Taken together, these data suggest that OA and DA impair brain mitochondrial energy homeostasis that could underlie at least in part the neuropathology of MCADD.

Oxidative stress induction by cis-4-decenoic acid: relevance for MCAD deficiency

Patients affected by medium-chain acyl-CoA dehydrogenase deficiency (MCADD) suffer from acute episodes of encephalopathy whose underlying mechanisms are poorly known. The present work investigated the in vitro effect of cis-4-decenoic acid (cDA), which accumulates in MCADD, on important parameters of oxidative stress in cerebral cortex of young rats. cDA markedly induced lipid peroxidation, as verified by the increased levels of spontaneous chemiluminescence and thiobarbituric acid-reactive substances. Furthermore, cDA significantly increased carbonyl formation and sulphydryl oxidation, which is indicative of protein oxidative damage, and promoted 2',7'-dihydrodichlorofluorescein oxidation. It was also observed that the non-enzymatic tissue antioxidant defenses were decreased by cDA, whereas the antioxidant enzyme activities catalase, superoxide dismutase and glutathione peroxidase were not altered. Moreover, cDA-induced lipid peroxidation and GSH reduction was totally blocked by free radical scavengers, suggesting that reactive species were involved in these effects. The data indicate that oxidative stress is induced by cDA in rat brain in vitro and that oxidative damage might be involved in the pathophysiology of the encephalopathy in MCADD.

Expanded newborn screening identifies maternal primary carnitine deficiency

Primary carnitine deficiency impairs fatty acid oxidation and can result in hypoglycemia, hepatic encephalopathy, cardiomyopathy and sudden death. We diagnosed primary carnitine deficiency in six unrelated women whose unaffected infants were identified with low free carnitine levels (C0) by newborn screening using tandem mass spectrometry. Given the lifetime risk of morbidity or sudden death, identification of adult patients with primary carnitine deficiency is an added benefit of expanded newborn screening programs.

The natural history of medium-chain acyl CoA dehydrogenase deficiency in the Netherlands: clinical presentation and outcome

OBJECTIVES

To describe the clinical presentation and long-term follow-up of a large cohort of patients with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency.

STUDY DESIGN

A nationwide, retrospective analysis of clinical presentation and follow-up in 155 Dutch patients with MCAD deficiency.

RESULTS

Most patients presented between 3 months and 5.1 years of age; 13% had symptoms as neonates not exclusively related to breast-feeding. An acute presentation before the diagnosis was made resulted in a mortality of 22% (25/114), whereas 21% (19/89) developed disabilities after the diagnosis. On follow-up, a total of 44 patients reported fatigue (35%; 28/80), muscle pain (31%; 25/80), and/or reduced exercise tolerance (39%; 31/80). Cardiac evaluation in 11 adult patients revealed no abnormalities in cardiac function explaining these complaints. Children with MCAD deficiency readily become overweight.

CONCLUSIONS

Mortality and morbidity were high in undiagnosed children with MCAD deficiency; establishment of the diagnosis significantly improves outcome. Strikingly, after the diagnosis and initiation of treatment, overweight and chronic complaints (fatigue, muscle pain, and reduced exercise tolerance) were prominent.

Sudden death in a young woman from medium chain acyl-coenzyme A dehydrogenase (MCAD) deficiency

Medium chain acyl-coenzyme A dehydrogenase (MCAD) deficiency is an inherited disorder of fatty acid metabolism that usually presents in early childhood. This case report describes a 19-year-old woman who presented with lethargy, disorientation, and vomiting. She had a cardiopulmonary arrest from which she could not be resuscitated 24h after the onset of the illness. Pre-mortem blood studies confirmed MCAD deficiency. An MCAD deficiency and other metabolic disorders lie within the differential diagnosis of a patient presenting with acutely altered mental status. The inheritance of MCAD deficiency and its clinical presentation, pathophysiology, treatment, and prevention are discussed.

Rapid, comprehensive screening of the human medium chain acyl-CoA dehydrogenase gene

Newborn screening by tandem mass spectrometry (MS/MS) identifies patients with medium chain acyl-CoA dehydrogenase (MCAD) deficiency the most frequently observed disorder of fatty acid oxidation. Molecular genetic analysis is becoming a common tool to confirm those identified as affected by prospective screening and for carrier detection in family studies. The A985G (K304E) mutation accounts for approximately 80% of mutant alleles in MCAD deficient patients, presenting symptomatically, while greater variability of mutant alleles is observed among cases identified through prospective screening. Aside from A985G, the mutation spectrum in MCAD deficient patients is heterogeneous such that comprehensive gene analysis is required. Traditionally the MCAD gene is assayed by sequencing the entire coding region. Although effective and definitive, this approach is expensive, turn around time is slow, and is poorly amenable to a clinical service molecular genetics laboratory. Dye-binding/high-resolution thermal denaturation is a rapid and homogeneous method by which to scan a PCR product for evidence of sequence aberration. PCR is performed in capillaries in the presence of the dsDNA-binding dye LCGreen I and subsequently the DNA/dye complexes are analyzed by high-resolution thermal denaturation. DNA sequencing was limited to fragments displaying abnormal melting profiles. Of 18 specimens analyzed, 11 have a genotype consistent with MCAD deficiency and seven have a genotype consistent with carrier status. Clinical and biochemical data corroborate that the genotype results identified the affected patients and differentiates them from carriers. The entire process is homogeneous requiring no post-PCR manipulation and is completed in under 3 h.

Newborn screening by tandem mass spectrometry for medium-chain Acyl-CoA dehydrogenase deficiency: a cost-effectiveness analysis

OBJECTIVE

To determine whether newborn screening by tandem mass spectrometry (MS/MS) for medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is cost-effective versus not screening and to define the contributions of disease, test, and population parameters on the decision.

METHODS

A decision-analytic Markov model was designed to perform cost-effectiveness and cost-utility analyses measuring the discounted, incremental cost per life-year saved and per quality-adjusted life-year saved of newborn screening for MCADD compared with not screening. A hypothetical cohort of neonates made transitions among a set of health states that reflected clinical status, morbidity, and cost. Outcomes were estimated for time horizons of 20 and 70 years. Probabilities and costs were derived from a retrospective chart review of a 32-patient cohort treated over the past 30 years at the Children's Hospital of Philadelphia, clinical experience with MCADD patient management, patient-family interviews, cost surveys, state sources, and published studies. In addition to older patients who came to medical attention by symptomatic presentation, our patient group included 6 individuals whose MCADD had been diagnosed by supplemental newborn screening. Estimates of the expected net changes in costs and life expectancy for MCADD screening were used to compute the incremental cost-effectiveness ratios. Sensitivity analyses were performed on key input variables, and 95% confidence intervals (CIs) were computed through second-order Monte Carlo simulations.

RESULTS

In our base-case analysis over the first 20 years of life, the cost of newborn screening for MCADD was approximately 11,000 dollars(2001 US dollars; 95% CI: <0-33,800 dollars) per life-year saved, or 5600 dollars (95% CI: <0-17,100 dollars) per quality-adjusted life-year saved compared with not screening. Over a 70-year horizon, the respective ratios were approximately 300 dollars (95% CI: <0-13,000 dollars) and 100 dollars (95% CI: <0-6900 dollars). The results were robust when tested over plausible ranges for diagnostic test sensitivity and specificity, MCADD prevalence, asymptomatic rate, and screening cost.

CONCLUSIONS

Simulation modeling indicates that newborn screening for MCADD reduces morbidity and mortality at an incremental cost below the range for accepted health care interventions. At the 70-year horizon, the model predicts that almost all of the additional costs of screening would be offset by avoided sequelae.

Adult presentation of MCAD deficiency revealed by coma and severe arrythmias

We report the case of a 33-year-old man who presented with headaches and vomiting. Soon after admission he became drowsy and agitated, developed ventricular tachycardia and his neurological state worsened (Glasgow coma score 6). Blood analysis showed respiratory alkalosis, hyperlactacidemia (8 mmol/l), hyperammonemia (390 micro mol/l) and hypoglycaemia (2.4 mmol/l). Subsequently, he developed supraventricular tachycardia, ventricular tachycardia and ultimately ventricular fibrillation resulting in cardiac arrest, which was successfully treated. A CT scan of the head revealed cerebral oedema. Whilst in the intensive care unit, he developed renal failure and rhabdomyolysis. The metabolic abnormalities seen at the time of admission normalised within 48 h with IV glucose infusion. Biological investigations, including urinary organic acids and plasma acylcarnitines, showed results compatible with MCAD deficiency. Mutation analysis revealed the patient was homozygous for the classical mutation A985G. This is one of only a few reports of severe cardiac arrhythmia in an adult due to MCAD deficiency. This condition is probably under-diagnosed in adult patients with acute neurological and/or cardiac presentations.

Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry

OBJECTIVE

2-methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of L-isoleucine metabolism. Only 4 affected individuals in 2 families have been described. One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy. A sibling of the first patient is asymptomatic after prenatal diagnosis and early treatment. Family investigations in the second family revealed that the patient's mother was also affected but asymptomatic.

METHODS

We report 8 additional patients identified by prospective newborn screening using tandem mass spectrometry.

RESULTS

Molecular genetic analysis performed for 3 of these patients revealed that all are homozygous for an 1165A>G mutation that causes skipping of exon 10 of the SBCAD gene. Although there was no obvious consanguinity, all patients belong to the Hmong, an ancient ethnic group that originated in China and constitutes only 0.8% and 0.6% of the Minnesota and Wisconsin population, respectively. Dietary treatment was initiated in the neonatal period. Except for 1 patient who developed mild muscle hypotonia, all patients remain asymptomatic at ages ranging from 3 to 14 months of age.

CONCLUSIONS

These cases suggest that SBCAD deficiency is another inborn error of metabolism detectable by newborn screening using tandem mass spectrometry. The continued efficacy of long-term dietary therapy instituted presymptomatically remains to be established.

Strategies for the diagnosis of mitochondrial fatty acid beta-oxidation disorders

Mitochondrial fatty acid beta-oxidation disorders (FAOD) are a group of clinically and biochemically heterogeneous inherited metabolic defects. The spectrum of phenotypes has expanded from hepatic encephalopathy to encompass myopathy, cardiomyopathy, peripheral neuropathy, sudden death and pregnancy complicated by fetal FAOD. Pre-symptomatic diagnosis is important to prevent morbidity and this is now achievable through newborn screening using tandem mass spectrometry (MS/MS). Moreover, most of the diagnosed defects are treatable and the prognosis is generally favourable. This article reviews the features of FAOD, critically evaluates methods of investigation including metabolite analyses in body fluids, in vitro oxidation rates and acylcarnitine profiling studies, enzymatic and mutational tests, and discusses genotype-phenotype correlation, treatment and monitoring options. Based on this knowledge, strategies for the biochemical investigation and differential diagnosis of patients presenting clinically, asymptomatic neonates detected by newborn screening, infants born after complications during late pregnancy, and cases of sudden death with suspected FAOD are presented. Laboratory investigation commonly begins with a search for diagnostic metabolites in physiological fluids, followed by in vitro functional studies if the initial findings are inconclusive, and confirmation by enzymology and molecular analyses. Occasionally a stress test in vivo may be required. At other times there may be no firm diagnosis achieved.

Disorders of fatty acid transport and mitochondrial oxidation: challenges and dilemmas of metabolic evaluation

Inborn errors of fatty acid transport and mitochondrial oxidation (FATMO) have drawn considerable attention in recent years for the rapid pace of discovery of new defects and an ever-increasing spectrum of clinical phenotypes. Several of these disorders are not detected by conventional biochemical investigations, even when a patient is symptomatic with fasting intolerance or functional failure of fatty acid dependent tissue(s). In our view, today's major challenges are the inclusion of FATMO disorders in newborn screening programs and the investigation of the role played by individual disorders in maternal complications of pregnancy, sudden and unexpected death in early life, and pediatric acute/fulminant liver failure. Dilemmas are found in the debate over the limitations, if any, to be imposed on the expansion of newborn screening using tandem mass spectrometry, in the provision of prenatal diagnosis for otherwise treatable disorders, and in the diagnostic workup of "unclassified" cases.