Sudden and unexpected neonatal death: a protocol for the postmortem diagnosis of fatty acid oxidation disorders

Carnitine-acylcarnitine translocase deficiency: a case report with autopsy

Fatty acid oxidation defects are a heterogeneous group of disorders related to the mitochondrial fatty acid oxidation pathway. Carnitine acylcarnitine translocase (CACT) is an enzyme responsible for the unidirectional transport of acylcarnitine across the inner mitochondrial membrane. This enzyme plays a crucial role in the oxidation of fatty acids. The autopsy pathology of the CACT deficiency is described in only a few cases. We describe the autopsy pathology of a child with CACT deficiency dominantly in the form of microvesicular steatosis of the hepatocytes, renal proximal tubular epithelia, cardiac myocytes, and rhabdomyocytes. The diagnosis was further confirmed on whole exome sequencing with compound heterozygous variants in the exon 1 (c.82G>T, p.Gly28Cys; likely pathogenic) and exon 5 (c.535G>A, p.Asp179Asn; uncertain significance) of the SLC25A20 gene. This case elucidates the histopathology of the liver and the detailed autopsy of a case of CACT deficiency from India.

Sudden cardiac death in the young: A consensus statement on recommended practices for cardiac examination by pathologists from the Society for Cardiovascular Pathology

Sudden cardiac death is, by definition, an unexpected, untimely death caused by a cardiac condition in a person with known or unknown heart disease. This major international public health problem accounts for approximately 15-20% of all deaths. Typically more common in older adults with acquired heart disease, SCD also can occur in the young where the cause is more likely to be a genetically transmitted process. As these inherited disease processes can affect multiple family members, it is critical that these deaths are appropriately and thoroughly investigated. Across the United States, SCD cases in those less than 40 years of age will often fall under medical examiner/coroner jurisdiction resulting in scene investigation, review of available medical records and a complete autopsy including toxicological and histological studies. To date, there have not been consistent or uniform guidelines for cardiac examination in these cases. In addition, many medical examiner/coroner offices are understaffed and/or underfunded, both of which may hamper specialized examinations or studies (e.g., molecular testing). Use of such guidelines by pathologists in cases of SCD in decedents aged 1-39 years of age could result in life-saving medical intervention for other family members. These recommendations also may provide support for underfunded offices to argue for the significance of this specialized testing. As cardiac examinations in the setting of SCD in the young fall under ME/C jurisdiction, this consensus paper has been developed with members of the Society of Cardiovascular Pathology working with cardiovascular pathology-trained, practicing forensic pathologists.

Metabolic autopsy with next generation sequencing in sudden unexpected death in infancy: Postmortem diagnosis of fatty acid oxidation disorders

The recent introduction of metabolic autopsy in the field of forensic science has made it possible to detect hidden inherited metabolic diseases. Since the next generation sequencing (NGS) has recently become available for use in postmortem examinations, we used NGS to perform metabolic autopsy in 15 sudden unexpected death in infancy cases. Diagnostic results revealed a case of carnitine palmitoyltransferase II deficiency and some cases of fatty acid oxidation-related gene variants. Metabolic autopsy performed with NGS is a useful method, especially when postmortem biochemical testing is not available.

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This is the first metabolic autopsy performed with next generation sequencing (NGS).

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We detected one case of CPT II deficiency and three cases of FAOD-related rare variants.

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Some of them had no specific abnormality except for genetic variants.

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These cases would be undetected without NGS.

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We advocate metabolic autopsy performed with NGS.

National Association of Medical Examiners Position Paper: Recommendations for the Postmortem Assessment of Suspected Head Trauma in Infants and Young Children

The National Association of Medical Examiners convened a panel to create a position paper for recommendations for the investigation of infant deaths due to inflicted head trauma. The correct certification of both the cause and manner of death is dependent upon an evaluation of all available data including information derived from the investigation, scene, postmortem examination, and ancillary studies. This paper provides recommendations for the forensic pathologist on what constitutes the dataset to be produced during the postmortem examination of infants who have died of, or have apparently died of, inflicted head trauma. Specifically, this paper describes 1) procedures, 2) ancillary laboratory tests, and 3) forms of documentation that are important in the investigation of these deaths. The evaluation and documentation of such infant deaths involves the production of a detail oriented and thoroughly documented examination that is independently reviewable to support the multitude of inquiries that may follow from the public and the criminal justice system.

Medium-chain acyl-CoA deficiency: outlines from newborn screening, in silico predictions, and molecular studies

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is a disorder of fatty acid oxidation characterized by hypoglycemic crisis under fasting or during stress conditions, leading to lethargy, seizures, brain damage, or even death. Biochemical acylcarnitines data obtained through newborn screening by liquid chromatography-tandem mass spectrometry (LC-MS/MS) were confirmed by molecular analysis of the medium-chain acyl-CoA dehydrogenase (ACADM) gene. Out of 324.000 newborns screened, we identified 14 MCADD patients, in whom, by molecular analysis, we found a new nonsense c.823G>T (p.Gly275∗) and two new missense mutations: c.253G>C (p.Gly85Arg) and c.356T>A (p.Val119Asp). Bioinformatics predictions based on both phylogenetic conservation and functional/structural software were used to characterize the new identified variants. Our findings confirm the rising incidence of MCADD whose existence is increasingly recognized due to the efficacy of an expanded newborn screening panel by LC-MS/MS making possible early specific therapies that can prevent possible crises in at-risk infants. We noticed that the “common” p.Lys329Glu mutation only accounted for 32% of the defective alleles, while, in clinically diagnosed patients, this mutation accounted for 90% of defective alleles. Unclassified variants (UVs or VUSs) are especially critical when considering screening programs. The functional and pathogenic characterization of genetic variants presented here is required to predict their medical consequences in newborns.

Sudden unexpected postnatal collapse of newborn infants: a review of cases, definitions, risks, and preventive measures

This study aimed to review available published reports concerning sudden unexpected postnatal collapse (SUPC) of apparently healthy infants within the first days of postnatal life, establish a structured presentation and delineate recommendations for preventive measures. All published reports of SUPC cases were retrospectively analyzed, and three not previously published SUPC cases at Karolinska University Hospital were detailed to exemplify the varying presentations and outcomes of SUPC. We found 398 published cases of SUPC occurring during first postnatal week. Estimated incidence of the SUPC of a presumably healthy infant after birth differs widely, ranging from 2.6 cases to 133 cases/100,000. However, definition, inclusion, and exclusion criteria vary substantially between reports. Our summary indicates that reported SUPC occurs more frequently than expected from recent surveys. About half of the infants die, and of the remaining survivors, half have neurological sequela. Of the 233 cases of sudden unexpected death described, no etiology was found in 153 cases. When a defined time for the SUPC event is described, approximately one third of reported events occur during the first 2 h, between 2 and 24 h and between 1 and 7 days after birth, respectively. Adequate education of caregivers and appropriate surveillance during the first days of newborns should enable us to save hundreds of lives.

Toddler Fatalities: The Terrible Twos

The majority of childhood deaths investigated by medical examiners and coroners are under the age of one, and medical examiners and coroners are well-versed in the challenges involved in investigating these fatalities. As infants mature to toddlers, there is a paradigm shift with a decrease in both the number of fatalities and the number of undetermined causes of death. A subset of these, however, remain undetermined, causing frustration for both the parents and medical examiner/coroner. In an effort to facilitate a differential diagnosis in these cases, death certificate data from the New York City Office of Chief Medical Examiner for deaths from one to four years of age over a five year period was examined. Of the 230 deaths investigated by the New York City Office of Chief Medical Examiner, the manner was natural in 39%, accident in 32%, homicide in 19%, therapeutic complication in 5%, and undetermined in 5%. Diligent scene investigation and a thorough histologic examination are key components to the investigation. While the lack of a cause of death in a portion of these undetermined deaths is due to limits in current postmortem techniques, a differential diagnosis for these deaths should include channelopathies, seizure disorders, and accidental injuries involving asphyxial mechanisms and inadvertent drug/toxin ingestion.

Routine Metabolic Testing is Not Warranted in Unexpected Infant Death Investigations

Inborn errors of metabolism (IEM) only rarely cause sudden unexpected infant death. Yet, postmortem metabolic screening is often ordered reflexively during infant death investigations, even in the absence of historical, clinical or autopsy findings suggestive of IEM. This retrospective descriptive study examines the impact of metabolic screening of infants who die suddenly in a medical examiner's jurisdiction. The study population included 135 cases, one of which was certified as death due to IEM with historical and pathologic findings suggestive of IEM and an abnormal postmortem screening study, one which was certified as death due to IEM with historical and pathologic findings suggestive of IEM and a negative postmortem screening study, and one which was certified as undetermined with pathologic features of IEM and a negative postmortem screening study, but also with features suggestive of accidental asphyxia. Nine cases had abnormal postmortem screens that were deemed to represent false positives. During the entire nine-year study of these 135 cases, the utilization of screening tests in cases without historical or autopsy features of IEM did not detect any unsuspected cases. IEM may rarely cause unexpected infant death, and it can be suggested by historical and autopsy findings. Thus, within the appropriate investigative and autopsy context, judicious use of metabolic screening tests is warranted. Caution is advised when interpreting negative screening studies with suggestive historical and/or autopsy findings as the success of testing decreases with increasing postmortem interval.

Incidence of medium-chain acyl-CoA dehydrogenase deficiency in Canada using the Canadian Paediatric Surveillance Program: Role of newborn screening

BACKGROUND

The incidence of medium-chain acyl-CoA dehydrogenase deficiency (MCADD) was estimated using the Canadian Paediatric Surveillance Program (CPSP) in Canada over a three-year period. Data regarding mutations associated with MCADD cases were collected wherever available.

METHODS

Data were collected over a 36-month period using a monthly mailed questionnaire distributed through the CPSP to more than 2500 Canadian paediatricians, medical geneticists and paediatric pathologists.

RESULTS AND CONCLUSIONS

During the three years of MCADD surveillance, 46 confirmed cases out of a total of 71 reported cases were found - an average of approximately 15 cases per year. This rate is lower than the initial estimate of approximately 30 cases per year of MCADD in Canada, based on the reported incidence of MCADD in the literature of approximately one in 10,000 to one in 20,000. All cases ascertained by newborn screening were asymptomatic. There were two deaths, both in jurisdictions without newborn screening for MCADD. The data support population-based newborn screening for MCADD.

The stillbirth collaborative research network postmortem examination protocol

After reviewing the state of knowledge about the scope and causes of stillbirth (SB) in a special workshop sponsored by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the participants determined that there is little guidance regarding the best use of postmortem examination (PM) to address the pathogenesis of stillbirth. In this report, we describe the PM procedure designed and used in the NICHD-supported Stillbirth Cooperative Research Network (SCRN). Perinatal pathologists, clinicians, epidemiologists, and biostatisticians at four tertiary care centers, a data coordinating center, and NICHD developed a standardized approach to perinatal PM, which was applied to a population-based study of stillbirth as part of the SCRN. The SCRN PM protocol was successfully instituted and used at the four medical centers. A total of 663 women with stillbirth were included: 620 delivered a single stillborn infant, 42 delivered twins, and one delivered triplets for a total of 676 stillborn infants. Of these women, 560 (84.5%) consented to PM (572 stillborn infants) that was conducted according to the SCRN protocol. A standardized PM protocol was developed to evaluate stillbirth consistently across centers in the United States. Novel testing and approaches that increase the yield of the PM can be developed using this model.

Pathology of the liver in obese and diabetic ob/ob and db/db mice fed a standard or high-calorie diet

Non-alcoholic fatty liver disease (NAFLD) is one of the commonest liver diseases in Western countries. Although leptin deficient ob/ob and db/db mice are frequently used as murine models of NAFLD, an exhaustive characterization of their hepatic lesions has not been reported to date, particularly under calorie overconsumption. Thus, liver lesions were characterized in 78 ob/ob and db/db mice fed either a standard or high-calorie (HC) diet, for one or three months. Steatosis, necroinflammation, apoptosis and fibrosis were assessed and the NAFLD activity score (NAS) was calculated. Steatosis was milder in db/db mice compared to ob/ob mice and was more frequently microvesicular. Although necroinflammation was usually mild in both genotypes, it was aggravated in db/db mice after one month of calorie overconsumption. Apoptosis was observed in db/db mice whereas it was only detected in ob/ob mice after HC feeding. Increased apoptosis was frequently associated with microvesicular steatosis. In db/db mice fed the HC diet for three months, fibrosis was aggravated while steatosis, necroinflammation and apoptosis tended to alleviate. This was associated with increased plasma β-hydroxybutyrate suggesting an adaptive stimulation of hepatic mitochondrial fatty acid oxidation (FAO). Nevertheless, one-third of these db/db mice had steatohepatitis (NAS ≥ 5), whereas none of the ob/ob mice developed non-alcoholic steatohepatitis under the same conditions. Steatosis, necroinflammation, apoptosis and fibrosis are modulated by calorie overconsumption in the context of leptin deficiency. Association between apoptosis and microvesicular steatosis in obese mice suggests common mitochondrial abnormalities. Enhanced hepatic FAO in db/db mice is associated with fibrosis aggravation.

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.

Drug-induced toxicity on mitochondria and lipid metabolism: mechanistic diversity and deleterious consequences for the liver

Numerous investigations have shown that mitochondrial dysfunction is a major mechanism of drug-induced liver injury, which involves the parent drug or a reactive metabolite generated through cytochromes P450. Depending of their nature and their severity, the mitochondrial alterations are able to induce mild to fulminant hepatic cytolysis and steatosis (lipid accumulation), which can have different clinical and pathological features. Microvesicular steatosis, a potentially severe liver lesion usually associated with liver failure and profound hypoglycemia, is due to a major inhibition of mitochondrial fatty acid oxidation (FAO). Macrovacuolar steatosis, a relatively benign liver lesion in the short term, can be induced not only by a moderate reduction of mitochondrial FAO but also by an increased hepatic de novo lipid synthesis and a decreased secretion of VLDL-associated triglycerides. Moreover, recent investigations suggest that some drugs could favor lipid deposition in the liver through primary alterations of white adipose tissue (WAT) homeostasis. If the treatment is not interrupted, steatosis can evolve toward steatohepatitis, which is characterized not only by lipid accumulation but also by necroinflammation and fibrosis. Although the mechanisms involved in this aggravation are not fully characterized, it appears that overproduction of reactive oxygen species by the damaged mitochondria could play a salient role. Numerous factors could favor drug-induced mitochondrial and metabolic toxicity, such as the structure of the parent molecule, genetic predispositions (in particular those involving mitochondrial enzymes), alcohol intoxication, hepatitis virus C infection, and obesity. In obese and diabetic patients, some drugs may induce acute liver injury more frequently while others may worsen the pre-existent steatosis (or steatohepatitis).

A review of sudden unexpected death in the young in British Columbia

BACKGROUND

Since 2008, all pediatric deaths in British Columbia have been reported to the coroner. The cause of death in pediatric sudden unexpected death (SUD) remains undetermined in 10% to 30% of cases. Before 2008, there was no standardized approach for referring relatives of SUD victims for follow-up medical testing to determine whether they were affected by the same condition. In the current era, genetic testing for primary electrical diseases can be used in cases of undetermined SUD when existing diagnostic methods fail.

OBJECTIVE

To improve the clinical care of surviving relatives of SUD victims, the current practice of assessment of SUD in British Columbia was reviewed. The study also aimed to determine the prevalence of SUD and sudden cardiac death, types of postmortem investigations performed in SUD, and the use of genetic testing for primary electrical diseases in SUD from 2005 to 2007.

METHODS

Cases involving individuals zero to 35 years of age, with a death due to natural disease or an undetermined cause were compiled from the British Columbia Coroners Service database. Cases were determined to be either sudden death due to a previously diagnosed condition or SUD.

RESULTS

In individuals zero to 35 years of age, the prevalence of SUD was 9.21 per 100,000 and the prevalence of sudden cardiac death was 5.26 per 100,000. There were 35 cases of SUD in which a cause of death was unidentified after autopsy (autopsy- negative SUD). Specimens were collected, and specialists were consulted in 86% of these cases in the pediatric population and 14% in the adult population. A suggestion was made to relatives to seek medical attention in 26% of the autopsy-negative SUDs, and molecular autopsy was discussed in 9% of cases but performed in none.

CONCLUSION

Currently, SUD in British Columbia is not managed in a way that optimizes a timely diagnosis for surviving relatives. A standardized protocol for SUD is needed to ensure optimization of diagnosis, genetic testing and referral of surviving relatives.

Cardiac Sodium Channel Dysfunction in Sudden Infant Death Syndrome

BACKGROUND

Mutations in genes responsible for the congenital long-QT syndrome, especially SCN5A, have been identified in some cases of sudden infant death syndrome. In a large-scale collaborative genetic screen, several SCN5A variants were identified in a Norwegian sudden infant death syndrome cohort (n=201). We present functional characterization of 7 missense variants (S216L, R680H, T1304M, F1486L, V1951L, F2004L, and P2006A) and 1 in-frame deletion allele (delAL586-587) identified by these efforts.

METHODS AND RESULTS

Whole-cell sodium currents were measured in tsA201 cells transiently transfected with recombinant wild-type or mutant SCN5A cDNA (hH1) coexpressed with the human beta1 subunit. All variants exhibited defects in the kinetics and voltage dependence of inactivation. Five variants (S216L, T1304M, F1486L, F2004L, and P2006A) exhibited significantly increased persistent sodium currents (range, 0.5% to 1.7% of peak current) typical of SCN5A mutations associated with long-QT syndrome. These same 5 variants also displayed significant depolarizing shifts in voltage dependence of inactivation (range, 5 to 14 mV) and faster recovery from inactivation, but F1486L uniquely exhibits a depolarizing shift in the conductance-voltage relationship. Three alleles (delAL586-587, R680H, and V1951L) exhibited increased persistent current only under conditions of internal acidosis (R680H) or when expressed in the context of a common splice variant (delQ1077), indicating that they have a latent dysfunctional phenotype.

CONCLUSIONS

Our present results greatly expand the spectrum of functionally characterized SCN5A variants associated with sudden infant death syndrome and provide further biophysical correlates of arrhythmia susceptibility in this syndrome.

Hypermetabolism of Fat in V1a Vasopressin Receptor Knockout Mice

[Arg8]Vasopressin (AVP) has an antilipolytic action on adipocytes, but little is known about the mechanisms involved. Here, we examined the involvement of the V1a receptor in the antilipolytic effect of AVP using V1a receptor-deficient (V1aR−/−) mice. The levels of blood glycerol were increased in V1aR−/− mice. The levels of ketone bodies, such as acetoacetic acid and 3-hydroxybutyric acid, the products of the lipid metabolism, were increased in V1aR−/− mice under a fasting condition. Triacylglyceride and free fatty acid levels in blood were decreased in V1aR−/− mice. Furthermore, measurements with tandem mass spectrometry determined that carnitine and acylcarnitines in serum, the products of β-oxidation, were increased in V1aR−/− mice. Most acylcarnitines were increased in V1aR−/− mice, especially in the case of 2-carbon (C2), C10:1, C10, C14:1, C16, C18:1, and hydroxy-18:1-carbon (OH-C18:1)-acylcarnitines under feeding rather than under fasting conditions. The analysis of tissue C2-acylcarnitine level showed that β-oxidation was promoted in muscle under the feeding condition and in liver under the fasting condition. An in vitro assay using brown adipocytes showed that the cells of V1aR−/− mice were more sensitive to isoproterenol for lipolysis. These results suggest that the lipid metabolism is enhanced in V1aR−/− mice. The cAMP level was enhanced in V1aR−/− mice in response to isoproterenol. The phosphorylation of Akt by insulin stimulation was reduced in V1aR−/− mice. These results suggest that insulin signaling is suppressed in V1aR−/− mice. In addition, the total bile acid, taurine, and cholesterol levels in blood were increased, and an enlargement of the cholecyst was observed in V1aR−/− mice. These results indicated that the production of bile acid was enhanced by the increased level of cholesterol and taurine. Therefore, these results indicated that AVP could modulate the lipid metabolism by the antilipolytic action and the synthesis of bile acid via the V1a receptor.

Fetal fatty acid oxidation disorders, their effect on maternal health and neonatal outcome: impact of expanded newborn screening on their diagnosis and management

Mitochondrial fatty acid oxidation disorders (FAOD) are recessively inherited errors of metabolism. Newborns with FAOD typically present with hypoketotic hypoglycemia, metabolic acidosis, hepatic failure, and cardiomyopathy. Late presentations include episodic myopathy, neuropathy, retinopathy, and arrhythmias. Sudden unexpected death can occur at any age and can be confused with sudden infant death syndrome. Some FAOD are associated with intrauterine growth restriction, prematurity, and pregnancy complications in the heterozygous mother, such as severe preeclampsia, acute fatty liver of pregnancy (AFLP), or hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome. Maternal pregnancy complications occur primarily in mothers carrying a fetus with long-chain l-3-hydroxyacyl CoA dehydrogenase deficiency or general trifunctional protein deficiencies. FAOD as a group represent the most common inborn errors of metabolism, and presymptomatic diagnosis of FAOD is the key to reduce morbidity and avoid mortality. The application of tandem mass spectrometry to newborn screening provides an effective means to identify most FAOD patients presymptomatically. At the beginning of 2005, 36 state newborn screening programs have mandated or adopted this technology resulting in a marked increase in the number of asymptomatic neonates with FAOD diagnosed. To ensure the long-term benefits of such screening programs, pediatricians and other health care providers must be educated about these disorders and their treatment.

Relative carnitine deficiency in autism

A random retrospective chart review was conducted to document serum carnitine levels on 100 children with autism. Concurrently drawn serum pyruvate, lactate, ammonia, and alanine levels were also available in many of these children. Values of free and total carnitine (p < 0.001), and pyruvate (p = 0.006) were significantly reduced while ammonia and alanine levels were considerably elevated (p < 0.001) in our autistic subjects. The relative carnitine deficiency in these patients, accompanied by slight elevations in lactate and significant elevations in alanine and ammonia levels, is suggestive of mild mitochondrial dysfunction. It is hypothesized that a mitochondrial defect may be the origin of the carnitine deficiency in these autistic children.

Unsuspected neonatal killers in emergency medicine

A neonate presenting to the emergency department can present a challenge to even the most experienced clinician. This article has focused on four deceiving and potentially devastating neonatal diseases. 1. Neonatal herpes is a potentially devastating illness without pathognomonic signs or symptoms. Early recognition and therapy can reduce mortality markedly. Although no specific sign or symptom is diagnostic,the diagnosis should be strongly considered in the presence of HSV risk factors, atypical sepsis, unexplained acute hepatitis, or focal seizure activity. Acyclovir therapy should be initiated before viral dissemination or significant CNS replication occurs. 2. Pertussis is a disease in which infants are at greatest risk of death or severe complication. Neonatal pertussis often presents in an atypical manner, lacking the classic signs and symptoms such as the "whoop."More common signs and symptoms include cough, feeding difficulty,low-grade fever, emesis, increasing respiratory distress, apnea, cyanosis,and seizures. Management should include hospitalization, supportive care, and antibiotics. 3. Congenital heart defects, particularly ductal-dependent lesions, may have an initial asymptomatic period that culminates in a rapidly progressive and fatal course. A neonate with CHD presents with shock refractory to volume resuscitation or pressor support. Resuscitative efforts are ineffective unless PGE, is administered. 4. Inborn errors of metabolism often are unsuspected because of their protean and heterogeneous nature. Signs and symptoms are subtle,are nonspecific, and often mimic other, more common diseases.An elevated index of suspicion, along with application and correct interpretation of a select few laboratory tests, is the key to making a diagnosis. Therapy is relatively straightforward and focused on resuscitation followed by prevention of catabolism and correction of specifically identified abnormalities. Although these disorders are relatively uncommon, prompt diagnosis and therapy can lead to a decrease in morbidity and mortality. The key is to maintain a high index of suspicion.

Postmortem findings in term neonates

Neonatal deaths in infants born at term are relatively rare in the USA, occurring in 0.9/1000 live births. Congenital malformations, perinatal asphyxia, infections and inborn errors of metabolism are the leading causes. Chromosomal malformation syndromes, congenital heart disease, pulmonary hypoplasia and severe neural tube defects comprise the majority of lethal malformations. Several skeletal dysplasias are lethal in the newborn infant. Group B Streptococcus still plays a major role in neonatal mortality while deaths due to other infectious agents have decreased. Hypoxic ischaemic encephalopathy is a significant cause of neonatal death. Inborn errors of metabolism have variable presentations but some, such as the fatty acid oxidation disorders, may present in neonates and cause sudden death.

MS/MS-based newborn and family screening detects asymptomatic patients with very-long-chain acyl-CoA dehydrogenase deficiency

OBJECTIVES

To determine whether asymptomatic persons with biochemical evidence of very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency identified through expanded newborn screening with tandem mass spectometry have confirmed disease.

STUDY DESIGN

We characterized 8 asymptomatic VLCAD-deficient individuals by enzyme and/or mutational analysis and compared them with clinically diagnosed, symptomatic patients with regard to mutations, enzyme activity, phenotype, and age of disease onset.

RESULTS

VLCAD molecular analyses in 6 unrelated patients revealed the previously reported V243A mutation, associated with hepatic or myopathic phenotypes, on 7/12 alleles. All other mutations were also missense mutations. Residual VLCAD activities of 6% to 11% of normal were consistent with milder phenotypes. In these identified individuals treated prospectively with dietary modification as preventive measures, clinical symptoms did not develop during follow-up.

CONCLUSIONS

MS/MS-based newborn screening correctly identifies VLCAD-deficient individuals. Based on mutational and enzymatic findings, these infants probably are at risk of future disease. Because life-threatening metabolic derangement can occur even in otherwise mild phenotypes, we advocate universal newborn screening programs for VLCAD deficiency to detect affected patients and prevent development of metabolic crises. Longer-term follow-up is essential to define outcomes, the definite risk of future disease, and appropriate treatment recommendations.

Incidence of autopsy findings in unexpected deaths of children and adolescents

Studies in various settings reveal that a significant percentage of autopsies demonstrate findings that were not previously clinically diagnosed. In the pediatric and adolescent age group, forensic examinations comprise a large percentage of total autopsies performed. We hypothesized that a similar number of previously undiagnosed findings would be present in this population and thus reviewed a series of autopsy reports from the Medical Examiners Office in the Arkansas Crime Laboratory. During 1997 through 1999, we performed 439 complete forensic autopsies on children and adolescents (age range 1 day to 19 years; median 18 months). Previously undiagnosed lesions were found in 173 (39%). Of these subjects, 68 (39%) had clinically significant pathology, 60 (35%) had insignificant pathology, and 45 (26%) had pathology of undetermined significance. Thirty-six subjects had lesions expected from a previously diagnosed condition. Of the total number of lesions found, 168 were inflammatory, 58 were congenital anomalies (48 unexpected), and 88 comprised miscellaneous other conditions. Infants <6 months of age were significantly more likely to have a previously undiagnosed lesson than children > 6 months (P <0.0001). Previously undiagnosed findings, mostly inflammatory, occur relatively frequently in pediatric and adolescent forensic autopsies and are more likely to occur in infants.

Treatment of carnitine deficiency

Carnitine deficiency is a secondary complication of many inborn errors of metabolism. Pharmacological treatment with carnitine not only corrects the deficiency, it facilitates removal of accumulating toxic acyl intermediates and the generation of mitochondrial free coenzyme A (CoA). The United States Food and Drug Administration (US FDA) approved the use of carnitine for the treatment of inborn errors of metabolism in 1992. This approval was based on retrospective chart analysis of 90 patients, with 18 in the untreated cohort and 72 in the treated cohort. Efficacy was evaluated on the basis of clinical and biochemical findings. Compelling data included increased excretion of disease-specific acylcarnitine derivatives in a dose-response relationship, decreased levels of metabolites in the blood, and improved clinical status with decreased hospitalization frequency, improved growth and significantly lower mortality rates as compared to historical controls. Complications of carnitine treatment were few, with gastrointestinal disturbances and odour being the most frequent. No laboratory or clinical safety issues were identified. Intravenous carnitine preparations were also approved for treatment of secondary carnitine deficiency. Since only 25% of enteral carnitine is absorbed and gastrointestinal tolerance of high doses is poor, parenteral carnitine treatment is an appealing alternative therapeutic approach. In 7 patients treated long term with high-dose weekly to daily venous boluses of parenteral carnitine through a subcutaneous venous port, benefits included decreased frequency of decompensations, improved growth, improved muscle strength and decreased reliance on medical foods with liberalization of protein intake. Port infections were the most troubling complication. Theoretical concerns continue to be voiced that carnitine might result in fatal arrhythmias in patients with long-chain fat metabolism defects. No published clinical studies substantiate these concerns. Carnitine treatment of inborn errors of metabolism is a safe and integral part of the treatment regime for these disorders.

Glucose-free medium exacerbates microvesicular steatosis in cultured skin fibroblasts of genetic defects of fatty acid oxidation. A novel screening test

Skin fibroblasts from patients with various fatty acid oxidation defects (FAOD) and four normal controls were subcultured in standard glucose-containing medium or in glucose-free medium simulating fasting. The FAOD fibroblasts developed microvesicular steatosis, which was greatly exacerbated in glucose-free medium. 'Rescue treatment' with glucose-containing medium was performed in the short-chain L-3-hydroxyacyl-CoA dehydrogenase-deficient (SCHADD) fibroblasts and resulted in a partial resolution of the steatosis and improved cellular viability. Transmission electron microscopy of autopsy specimens from the SCHADD patient demonstrated that most renal interstitial fibroblasts and approximately 50% of fibroblasts in the heart had microvesicular steatosis. The demonstration of microvesicular steatosis in parenchymal and/or cultured skin fibroblasts may provide important and cost-effective screening tools for the detection of genetic defects of fatty acid oxidation.

A survey of Japanese patients with mitochondrial fatty acid beta-oxidation and related disorders as detected from 1985 to 2000

A clinical survey of Japanese patients with mitochondrial fatty acid beta-oxidation and related disorders (FAODs) was performed with questionnaires sent to 187 institutions, where inborn errors of metabolism could be managed in Japan, including a search of related literature published between 1985 and 2000. Sixty-four patients with ten types of FAODs were found. Carnitine palmitoyltransferase 2 deficiency and glutaric aciduria type 2 were most common (17 and 14 patients, respectively). As of 2000, there were no patients with medium-chain acyl-CoA dehydrogenase deficiency, which is common in Caucasians. Age at onset was under 2 years in 38 (59%) of the patients. Eight (13%) patients had neonatal onset. Twenty-one (55%) of the 38 children with an initial attack under 2 years of age had acute encephalopathy or a Reye syndrome-like illness. Half of the patients presented within 2 years of birth died or were handicapped. On the other hand, 19 (79%) of the 24 with onset after 2 years of age had muscle symptoms and 23 (96%) of the 24 grew and developed normally. Though the precise incidence of FAODs in Japan is still unknown, as a consequence of the development of diagnostic procedures the number of FAOD cases being diagnosed appears to have increased. Mass screening for FAODs during the neonatal period will greatly aid in prevention of attacks and related effects.

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.

Laboratory diagnosis of metabolic myopathies

The metabolic myopathies are a heterogeneous group of disorders inherited by a variety of modes that include gene defects in both the nuclear and mitochondrial genomes. Many factors impact on the expression of the pathogenic mutations that cause these disorders including genetic background, environmental factors, and coexisting disorders. Molecular technology has greatly improved the ability to make definitive diagnoses in many of the metabolic myopathies in the last decade and particularly has demonstrated that the wide diversity in the severity of mutations contributes to understanding genotype-phenotype correlations. In some cases, molecular testing obviates the necessity to perform an invasive muscle biopsy. However, it is also clear that the diagnostic yield from molecular testing is incomplete and particularly low among the mitochondrial myopathies as a group, ranging from approximately 6% to 19% in well-classified high-risk groups. Therefore, it is often essential to combine clinical, biochemical, histopathologic, and molecular data for each patient in order to arrive at a definitive diagnosis. The approach to the laboratory diagnosis of metabolic myopathies is described emphasizing both noninvasive and invasive testing, highlighting the molecular methodologies with the benefits and disadvantages of each technology, and documenting how to determine whether patients have coexisting disorders.

Targeted disruption of the pituitary adenylate cyclase-activating polypeptide gene results in early postnatal death associated with dysfunction of lipid and carbohydrate metabolism

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a hormone belonging to the glucagon superfamily of hormones. These hormones are known to play important roles in metabolism and growth. PACAP is a neuropeptide that causes accumulation of cAMP in a number of tissues and affects the secretion of other hormones, vasodilation, neural and immune functions, as well as the cell cycle. To determine whether PACAP is essential for survival and to evaluate its function(s), we have generated mice lacking the PACAP gene via homologous recombination. We found that most PACAP null mice died in the second postnatal week in a wasted state with microvesicular fat accumulation in liver, skeletal muscle, and heart. Gas chromatography-mass spectrometry showed that fatty acid beta-oxidation in liver mitochondria of PACAP(-/-) mice was not blocked based on the distribution of 3-hydroxy-fatty acids (C6-16) in the plasma. Instead, increased metabolic flux through the beta-oxidation pathway was suggested by the presence of ketosis. Also, serum triglycerides and cholesterol were significantly higher (2- to 3-fold) in PACAP null mice than littermates. In the fed state, both serum insulin and blood glucose were normal in 5-d-old null mice compared with their littermates. In contrast, fasted PACAP null pups had a significant increase in insulin, but a decrease in blood glucose compared with littermates. Glycogen in the liver was reduced. These results suggest PACAP is a critical hormonal regulator of lipid and carbohydrate metabolism.

Electrospray Tandem Mass Spectrometry for Analysis of Acylcarnitines in Dried Postmortem Blood Specimens Collected at Autopsy from Infants with Unexplained Cause of Death

Background: Deaths from inherited metabolic disorders may remain undiagnosed after postmortem examination and may be classified as sudden infant death syndrome. Tandem mass spectrometry (MS/MS) may reveal disorders of fatty acid oxidation in deaths of previously unknown cause.

Methods: We obtained filter-paper blood from 7058 infants from United States and Canadian Medical Examiners. Acylcarnitine and amino acid profiles were obtained by MS/MS. Specialized interpretation was used to evaluate profiles for disorders of fatty acid, organic acid, and amino acid metabolism. The analyses of postmortem blood specimens were compared with the analyses of bile specimens, newborn blood specimens, and specimens obtained from older infants at risk for metabolic disorders.

Results: Results on 66 specimens suggested diagnoses of metabolic disorders. The most frequently detected disorders were medium-chain and very-long-chain acyl-CoA dehydrogenase deficiencies (23 and 9 cases, respectively), glutaric acidemia type I and II deficiencies (3 and 8 cases, respectively), carnitine palmitoyl transferase type II/translocase deficiencies (6 cases), severe carnitine deficiency (4 cases), isovaleric acidemia/2-methylbutyryl-CoA dehydrogenase deficiencies (4 cases), and long-chain hydroxyacyl-CoA dehydrogenase/trifunctional protein deficiencies (4 cases).

Conclusions: Postmortem metabolic screening can explain deaths in infants and children and provide estimates of the number of infant deaths attributable to inborn errors of metabolism. MS/MS is cost-effective for analysis of postmortem specimens and should be considered for routine use by Medical Examiners and pathologists in unexpected/unknown infant and child death.

Laboratory evaluation of urea cycle disorders

The urea cycle disorders (UCDs) represent a group of inherited metabolic diseases with hyperammonemia as the primary laboratory abnormality. Affected individuals may become comatose or die if not treated rapidly. Diagnosis of a UCD requires a high index of suspicion and judicious use of the laboratory. It is important to rule out other conditions causing hyperammonemia that may require different treatment. The astute clinician may suspect a specific UCD in the appropriate clinical setting, but only laboratory results can confirm a specific diagnosis. The importance of the laboratory in helping the clinician to differentiate among various causes of hyperammonemia, in confirming a specific UCD, in carrier testing, and in prenatal diagnostic testing is highlighted in this review.

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.

New developments in the pathophysiology, clinical spectrum, and diagnosis of disorders of fatty acid oxidation

Fatty acid oxidation disorders are among the most common inborn errors of metabolism affecting infants and children. Recognition of this family of defects is critical because careful dietary monitoring, avoidance of fasting, and prompt intervention during common childhood illness can prevent catastrophic cardiac and metabolic decompensation. This review focuses on new molecular and clinical diagnostic aspects of several of these disorders. Recent papers highlight the recognition that the clinical spectrum of disorders of fatty acid oxidation goes far beyond the stereotypical Reyes-like presentation or cardiomyopathy, and now encompasses more cases of sudden infant death syndrome, fulminant hepatic failure, and severe complications during pregnancy.

Inborn errors of mitochondrial fatty acid oxidation

Inborn errors of the mitochondrial beta-oxidation of long-chain fatty acids represent an evolving field of inherited metabolic disease. Fatty acid oxidation defects demonstrate an abnormal response to the process of fasting adaptation and affect those tissues that utilize fatty acids as an energy source. These tissues include cardiac and skeletal muscle and liver. Muscle directly uses fatty acids as an energy source whilst hepatic metabolism of fatty acids is mostly directed toward the synthesis of ketone bodies for energy utilization by tissues such as brain. The clinical phenotypes of fatty acid oxidation disorders include disease of one or more of these fatty acid-metabolizing tissues. In this review, we provide an overview of the pathway, discuss the disorders that are well established, and describe recent advances in the field. Currently available diagnostic procedures are critically evaluated.