串联质谱技术选择性筛查遗传代谢病高危患儿552例初步分析

目的：应用串联质谱（tandem mass spectrometry, MS/MS）技术进行遗传代谢病（IEM）高危儿筛查,初步了解我国 IEM 的发病种类和阳性率,为其有效防治提供科学依据。方法：利用MS/MS技术对在河北省石家庄市8所省、市级医院就医的552例可疑 IEM 患儿的血液样本进行 IEM 筛查。结果：发现阳性患儿64例,阳性率为11.6%。其中甲基丙二酸血症或丙酸血症33例,苯丙酮尿症2例,肉碱棕榈酰转移酶缺乏Ⅰ型3例,长链酰基辅酶 A 脱氢酶缺乏症1例,中链酰基辅酶A脱氢酶缺乏症2例,枫糖尿症6例,短链酰基辅酶A脱氢酶缺乏症2例,戊二酸血症Ⅰ型2例,异戊酸血症2例,同型胱氨酸尿症2例,肉碱缺乏症4例,酪氨酸血症1例,精氨酸琥珀酸尿症1例,瓜氨酸血症2例,精氨酸血症1例。结论：MS/MS技术是筛查诊断IEM的有效工具。     

Carnitine Deficiency in Inherited Organic Acid Disorders and Reye Syndrome

A large quantity of propionylcarnitine in the urine of patients with propionic acidemia and methylmalonic aciduria was demonstrated. The amount excreted depended on the administered L-carnitine dose from 25 to 75 mg/kg/day. A high level of propionylcarnitine was also detected in the amniotic fluid of fetuses at risk of methylmalonic aciduria. Glutaric aciduria type 1 was characterized by excessive urinary excretion of glutarylcarnitine. In a neonate with glutaric aciduria type 2, several specific acylcarnitines were detected in the urine. These included isovaleryl-, acetyl-, isobutyryl-, and butyrylcarnitine as major carnitine esters and glutaryl-, and octanoylcarnitine as minor components. However, the pattern of acylcarnitines excreted changed from isovalerylcarnitine (via leucine) to isobutyrylcarnitine (via valine) during early life. In patients diagnosed as Reye syndrome, tissue carnitine deficiency was not always recognized and no decrease in the free/total carnitine ratio was found in the liver or muscle. The clinical and pathophysiological manifestations seen in these disorders are considered to relate to mitochondrial activity. Therefore, it is necessary to measure acylcarnitine fractions in the urine in order to obtain more precise information about mitochondrial function because carnitine and acylcarnitine compounds may express the metabolic state of mitochondria.     

A study of urinary metabolites in patients with dicarboxylic aciduria for differential diagnosis

Dicarboxylic aciduria (DCA-uria) is a relatively common finding in the screening of organic acidemias by gas chromatography/mass spectrometry (GC/MS). A considerable number of patients with DCA-uria are involved in disturbances of mitochondrial and peroxisomal fatty acid β-oxidation. The differential diagnosis of DCA-uria was investigated using a combination of organic acid analysis by GC/MS, carnitine determination, acylcarnitines by fast atom bombardment/mass spectrometry (FAB/MS) and acylglycines by stable-isotope dilution analysis. The relative distribution of urinary metabolites was examined in 46 patients with DCA-uria of different origins, including physiological ketosis of childhood, disorders of propionic acid metabolism, glutaric aciduria type II, Zellweger syndrome and patients who were clinically diagnosed as having Reye syndrome. Zellweger syndrome seemed to be distinguishable from other disorders by the high sebacic acid/adipic acid ratio of DCA-uria and increased excretion of 4-hydroxyphenyllactic acid and 2-hydroxysebacic acid. The mild form of glutaric aciduria type II was often missed by current organic acid analysis alone, but was readily diagnosed by acylcarnitine and acylglycine determination. The ratio of free/total carnitine was low in most of the DCA-uria patients except for two of five cases of Zellweger syndrome and one of three cases of Reye syndrome. The acylcarnitine analysis by FAB/MS showed adipyl-, suberyl-, sebacyl- or dodecanedioylcarnitine as major peaks in most of these patients, although these were not specific. Disease-specific peaks were detectable only in congenital organic acidemias such as glutaric aciduria type II, methylmalonic acidemia and propionic acidemia.     

Diagnostic and therapeutic implications of medium-chain acylcarnitines in the medium-chain acyl-coA dehydrogenase deficiency

The medium-chain acyl-coA dehydrogenase deficiency is one of several metabolic disorders presenting clinically as Reye syndrome. Evidence is presented for a characteristic organic aciduria that distinguishes this disorder from Reye syndrome and other masqueraders characterized by dicarboxylic aciduria. The key metabolites, suberylglycine and hexanoylglycine, are excreted in high concentration only when the patients are acutely ill. More significantly, using novel techniques in mass spectrometry, the medium-chain defect is shown to be characterized by excretion of specific medium-chain acylcarnitines, mostly octanoylcarnitine, without significant excretion of a normal metabolite, acetylcarnitine, in four patients with documented enzyme deficiency. Similar studies on the urine of two patients reported with Reye-like syndromes of unidentified etiology have suggested the retrospective diagnosis of medium-chain acyl-coA dehydrogenase deficiency. Administration of L-carnitine to medium-chain acyl-coA dehydrogenase deficiency patients resulted in the enhanced excretion of medium-chain acylcarnitines. Octanoylcarnitine is prominent in the urine both prior to and following L-carnitine supplementation. The detection of this metabolite as liberated octanoic acid, following ion-exchange chromatographic purification and mild alkaline hydrolysis, provides a straightforward diagnostic procedure for recognition of this disorder without subjecting patients to the significant risk of fasting. In view of the carnitine deficiency and the demonstrated ability to excrete the toxic medium-chain acyl-coA compounds as acylcarnitines, a combined therapy of reduced dietary fat and L-carnitine supplementation (25 mg/kg/6 h) has been devised and applied with positive outcome in two new cases.     

Carnitine in the treatment of methylmalonic aciduria (MMA)

Carnitine metabolism was studied and a therapeutic trial with L-carnitine was undertaken in 3 patients with methylmalonic aciduria. Prior to carnitine therapy, the concentration of free carnitine was diminished and the contribution of acylated carnitine to total carnitine was increased in both plasma and urine. During a metabolic crisis, in a patient the intravenous administration of L-carnitine greatly increased, the urinary excretion of acylcarnitine and the plasma concentration of methylmalonic acid fell. In all 3 patients, the chronic oral administration of L-carnitine resulted in the normalisation of the plasma free carnitine concentrations and an increased urinary excretion of carnitine esters. One patient clearly showed clinical improvement under carnitine therapy. The administration of L-carnitine to patients with methylmalonic aciduria results in an increased elimination of toxic propionyl groups and thus to a regeneration of intramitochondrial CoA. In conjunction with appropriate dietary measures, this may improve the metabolic situation of these patients.     

Branched-chain organic acidurias

Branched chain organic acidurias are a group of disorders that result from an abnormality of specific enzymes involving the catabolism of branched chain amino acids (leucine, isoleucine, valine). Maple syrup urine disease (MSUD), isovaleric acidaemia (IVA), propionic aciduria (PA) and methylmalonic aciduria (MMA) represent the most commonly encountered abnormal organic acidurias. All these four disorders present in neonates as a neurologic distress of the intoxication type with either ketosis or ketoacidosis and hyperammonaemia. There is a free interval between birth and clinical symptoms. MMA, PA and IVA present with a severe dehydration, leuconeutropenia and thrombopenia which can mimic sepsis. All these disorders can be diagnosed by identifying acylcarnitine and other organic acid compounds in plasma and urine by gas chromatography mass spectrometry or tandem MS-MS. These disorders are amenable to treatment by removing toxic compounds and by using special diets and carnitine.     

Ethylmalonic/adipic aciduria: effects of oral medium-chain triglycerides, carnitine, and glycine on urinary excretion of organic acids, acylcarnitines, and acylglycines

A 9-y-old girl with ethylmalonic/adipic aciduria was hospitalized to determine the possible therapeutic efficacy of oral carnitine and glycine supplementation. To provoke a mild metabolic stress, her diet was supplemented with 440 mg/kg/d of medium-chain triglycerides. She was treated successively with carnitine (100 mg/kg/d) for 5 d, neither carnitine nor glycine for 2 d, and then glycine (250 mg/kg/d) for 6 d. Consecutive 12-h urine collections were obtained throughout the entire period. The urinary excretion of eight organic acids, four acylglycines, and four acylcarnitines, which accumulate as a result of a metabolic block of five mitochondrial acyl-CoA dehydrogenases, were quantitatively determined by capillary gas chromatography, stable isotope dilution gas chromatography/mass spectrometry, and radioisotopic exchange HPLC, respectively. The excretion of each group of metabolites was calculated as the mean percentage of total output (mumol/24 h) during the four phases of the protocol (organic acids/acylglycines/acylcarnitines = 100.0%): 1) regular diet (3 d); 88.1/10.8/1.1; 2) medium-chain triglyceride supplementation (4); 82.5/15.6/1.9; 3) medium-chain triglycerides plus carnitine (5); 79.2/8.2/12.6; and 4) medium-chain triglycerides plus glycine (6); 81.0/18.7/0.3. Comparison between total and individual excretion of acylglycines and acylcarnitines indicates that oral glycine supplementation enhanced the conjugation and excretion of fatty acyl-CoA intermediates as efficiently as carnitine. We propose that oral glycine supplementation should be considered in the treatment of other inborn errors of metabolism associated with abnormal urinary excretion of acylglycines.     

Metabolic response to carnitine in methylmalonic aciduria. An effective strategy for elimination of propionyl groups.

Patients with methylmalonic aciduria have an excessive intramitochondrial accumulation of acylcoenzyme A compounds that may reduce the availability of free coenzyme A (CoA) for normal metabolic requirements, producing profound metabolic disturbances. Giving carnitine to a patient with methylmalonic aciduria produced an increase in hippurate excretion (an index of intramitochondrial adenosine triphosphate (ATP) and CoA availability), a large increase in short chain urinary acylcarnitines, and a reduction in excretion of methylmalonate and methylcitrate. These acylcarnitines were shown by fast atom bombardment and B/E linked scan mass spectrometry to be propionylcarnitine and acetylcarnitine. Carnitine acts by removing (detoxifying) propionyl groups, thereby releasing CoA and restoring ATP biosynthesis and concentrations towards normal. L-carnitine may play a central role in maintenance of mitochondrial and cellular homoeostasis in methylmalonic aciduria and propionic acidaemia. These principles may provide an approach to the treatment of this and other disorders, inherited and acquired, in which accumulation of acyl CoA metabolites results in sequestration of free CoA, thereby perturbing metabolic homoeostasis.     

Quantitation of urinary carnitine esters in a patient with medium-chain acyl-coenzyme A dehydrogenase deficiency: effect of metabolic state and L-carnitine therapy

Urinary carnitine esters were quantitated in an infant with medium-chain acylcoenzyme A dehydrogenase deficiency by means of a highly sensitive and specific radioisotopic exchange high-pressure liquid chromatography method. During fasting, the excretion of free carnitine and of acetylcarnitine, octanoylcarnitine, and hexanoylcarnitine was increased. The fractional tubular reabsorption of free carnitine was decreased, suggesting a renal leak of free carnitine. In the symptom-free, fed state, only minor amounts of free carnitine and of short-chain acylcarnitine, octanoylcarnitine, and hexanoylcarnitine were present in urine, and carnitine loss occurred in the form of "other" carnitine esters not exceeding that of control subjects. During L-carnitine therapy, the excretion of free carnitine, short-chain acylcarnitine, octanoylcarnitine, and hexanoylcarnitine, and particularly of "other" carnitine esters, was increased, suggesting a possible detoxifying effect of administered carnitine that is not confined to the elimination of octanoic and hexanoic acids. The employed method detects very low urinary concentrations of octanoylcarnitine and hexanoylcarnitine (less than 1 mumol/L) characteristic of medium-chain acyl-coenzyme A dehydrogenase deficiency and may be useful in screening for this disease, which has been associated with sudden infant death.     

串联质谱技术在有机酸血症筛查中的应用研究

目的探讨串联质谱技术在遗传性代谢病高危儿童有机酸血症筛查和诊断中的意义。方法遗传性代谢病高危儿童1000例,男642例,女358例,年龄中位数为2岁(5天～15岁),手指采血,滴于滤纸片上。取直径3mm的干血滤纸片放入96孔聚丙烯板,经含酰基肉碱内标的甲醇萃取,盐酸正丁醇衍生后,进行串联质谱分析。结果1000例高危儿童中筛查并诊断有机酸血症40例(4．0％),其中甲基丙二酸血症20例,丙酸血症6例,异戊酸血症3例,戊二酸血症Ⅰ型3例,戊二酸血症Ⅱ型3例,β-甲基巴豆酰辅酶A羧化酶缺乏症1例,β-羟基．3．甲基戊二酰辅酶A裂解酶缺乏症1例,生物素酶缺乏症2例,β-酮硫解酶缺乏症1例。患儿临床表现主要为运动和智力发育落后、抽搐、意识障碍、肌张力低下、呕吐和喂养困难等。常规实验室检查主要表现为酸中毒、高血氨、高乳酸血症和低血糖等。结论串联质谱技术能够通过检测血滤纸片中的不同酰基肉碱浓度,对部分有机酸血症进行快速筛查和诊断,结合尿气相色谱／质谱技术,有助于提高有机酸血症诊断的准确性。     

Metabolic studies of carnitine in a child with propionic acidemia

Carnitine metabolism was studied in a 7-y-old boy with propionic acidemia due to an almost total deficiency of propionyl-CoA carboxylase. The initial diagnosis was made at 3 wk of age followed by numerous episodes of metabolic acidosis despite a low-content branch-chain amino acid diet containing supplemental biotin. Although clinically stable and in a nonacidotic state, the plasma concentration of total carnitine was normal (38.9 microM; normal = 46 +/- 10, mean +/- SD, n = 30) whereas free carnitine was decreased (5.7 microM; normal = 37 +/- 8) and short-chain acylcarnitines were increased (28.6 microM; normal = 5.7 +/- 3.5). Skeletal muscle and liver specimens obtained at open biopsy had low total and free carnitine contents and increased ratio of short-chain acylcarnitines to free carnitine. Short-chain acylcarnitine content was low in liver but increased in skeletal muscle. The liver contained fatty vacuoles, enlarged mitochondria with paracrystalline inclusions, and numerous peroxisomes whereas the skeletal muscle also had lipid vacuoles and an increase in number and size of mitochondria. A carnitine challenge test (100 mg L-carnitine/kg body wt via a gastrostomy tube) resulted in a peak plasma carnitine concentration at 120 min. With maintenance therapy of 100 mg L-carnitine/kg/day the plasma free carnitine remained relatively low, the plasma glycine concentration decreased, and urinary acylcarnitine excretion increased. This study demonstrates that the alterations in carnitine and its derivatives observed in plasma and urine reflect the same type of altered distribution in tissue and provides further data on the effects of L-carnitine therapy.     

Urinary medium-chain acylcarnitines in medium-chain acyl-CoA dehydrogenase deficiency, medium-chain triglyceride feeding and valproic acid therapy: sensitivity and specificity of the radioisotopic exchange/high performance liquid chromatography method.

To determine the sensitivity and specificity of detecting urinary medium-chain acylcarnitines for the diagnosis of MCAD deficiency, 114 urine specimens from 75 children with metabolic diseases and controls were analyzed in a blinded fashion using a radioisotopic exchange/HPLC method. All 47 patients with MCAD deficiency were correctly diagnosed using the criterion hexanoylcarnitine or octanoylcarnitine peak areas larger than those of other medium-chain acylcarnitines. The majority of them were tested during the asymptomatic state without L-carnitine loading. Four patients with other defects of fatty acid oxidation and three patients receiving valproic acid had a similar acylcarnitine excretion pattern. To further examine the specificity of the method, eight infants receiving a diet enriched with medium-chain triglycerides and 13 additional patients receiving valproic acid were studied. Most of these also tested positive for MCAD deficiency by the above criterion. Analysis by a new gas chromatographic-mass spectrometric procedure revealed that octanoylcarnitine, not valproylcarnitine, was the most abundant medium-chain carnitine ester excreted by a patient treated with valproic acid. Quantitation of urinary hexanoylcarnitine and octanoylcarnitine showed considerable overlap among patients with MCAD deficiency and those receiving valproic acid or a medium-chain triglyceride-enriched diet. MCAD deficiency can be reliably detected in urine specimens by this method without the need for prior carnitine loading. However, other defects in fatty acid oxidation must be differentiated from MCAD deficiency, and a history of medium-chain triglyceride or valproic acid administration must be considered if the diagnosis of MCAD deficiency is sought through analysis of urinary acylcarnitines.     

<Emphasis Type="Italic">N</Emphasis>-carbamylglutamate treatment for acute neonatal hyperammonemia in isovaleric acidemia

Hyperammonemia occurs mainly in patients with branched-chain organic acidemias such as propionic, methylmalonic, and isovaleric acidemias. Its pathophysiological process is mainly via the competitive inhibition of N-acetylglutamate synthetase. Oral carglumic acid (N-carbamylglutamate) administration can correct hyperammonemia in neonates with propionic and methylmalonic acidemias, thus avoiding dialysis therapy. Isovaleric acidemia is an autosomal recessive disease of leucine metabolism due to deficiency of isovaleryl-CoA dehydrogenase. For the first time, we report a neonate with isovaleric acidemia, whose plasma ammonia concentration dropped dramatically after one oral load of carglumic acid. This experience suggests that carglumic acid could be considered for acute hyperammonemia resulting from isovaleric acidemia. However, trials with more patients are needed.     

Screening newborns for multiple organic acidurias in dried filter paper urine samples: method development

Screening urine for inherited and acquired organic acidurias in newborns has the potential of preventing severe disease, mental retardation, and death. A method for screening dried urine filter paper samples for acidic markers of at least 20 different metabolic conditions has been developed. These conditions include, among others, maple syrup urine disease; methylmalonic, propionic, isovaleric, glutaric, and hydroxymethylglutaric acidurias; methylcrotonylglycinuria; medium-chain acyl-CoA dehydrogenase deficiency; inherited vitamin responsive disorders B12, biotin, B2), and acquired deficiencies of these vitamins. The preparation of the urine extract is identical to the method we use to screen infants for neuroblastoma. Screening is based on a highly sensitive and specific determination of eight organic acid markers by an automated computerized gas chromatography mass spectrometry system using selected ion monitoring. The markers used for screening are methylmalonic acid, 2-hydroxyisocaproic acid, glutaric acid, propionylglycine, isovalerylglycine, 3-methylcrotonylglycine, hexanoylglycine, and 3-phenylpropionylglycine. The extraction efficiencies of these acids from dried filter paper were similar to extraction from water, ranging from about 40% to 80%, except for propionylglycine which showed a low extraction efficiency of 11-13%. The stability of these acids on filter paper exposed to room air and temperature over a period of 15 d was adequate for the use of this collection method for organic aciduria screening. Normal levels, adjusted to urinary creatinine, were established for these acids in 519 urine filter paper samples obtained from 3-wk-old newborns. This screening method was tested on samples obtained from 12 patients with known organic acidurias including stored urine filter paper collected at 3-wk of age from two infants later found to have organic acidurias.     

Tissue carnitine homeostasis in very-long-chain acyl-CoA dehydrogenase-deficient mice

Deficiency of very-long-chain acyl-CoA dehydrogenase (VLCAD) is the most common long-chain fatty acid oxidation defect and presents with heterogeneous clinical manifestations. Accumulation of long-chain acylcarnitines and deficiency of free carnitine have often been proposed to play an important role in disease pathogenesis. The VLCAD-deficient mouse exhibits similar clinical and biochemical phenotypes to those observed in humans and, therefore, represents an excellent model to study VLCAD deficiency. We measured carnitine and acylcarnitine profiles in liver, skeletal muscle (SkM), bile, and blood from VLCAD knock-out mice and controls under nonstressed and various stress conditions. Carnitine and acylcarnitines were extracted from body fluids with methanol and from tissues with acetonitrile, respectively, and were analyzed as their butyl esters using electrospray ionization tandem mass spectrometry. Fasting combined with a cold challenge for 8 h significantly induced liver long-chain acylcarnitine and free carnitine production. Acylcarnitines in SkM predominantly accumulated during exercise with a concomitant decrease of free carnitine. Changes in blood free carnitine did not correlate with carnitine homeostasis in liver and SkM. Our results demonstrate different tissue-specific long-chain acylcarnitine profiles in response to various stressors, which may be of importance with respect to the heterogeneous clinical manifestations of VLCAD deficiency in humans. Furthermore, we conclude that carnitine biosynthesis in the liver seems sufficiently active to maintain liver carnitine levels during increased demand. Our data suggest that carnitine supplementation in long-chain beta-oxidation defects may not be required, and blood carnitine concentrations do not reflect tissue carnitine homeostasis.     

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??Methylmalonic aciduria??MMA?? is the most common organic acidemia in China. Its biochemical diagnostic indexes are the increased propionic carnitine?? the increased ratio of propiylcarnitine/acetylcarnitine in blood??and the increased methylmalonic acid and methyl citrate in urine. For patients combined with homocysteinemia??combined MMA???? homocysteine is also increased in blood. As for genetic diagnosis??pathogenic variations are mainly exposed in the following genes??MUT??MMAA??MMAB??MMACHC??MMADHC?? LMRD1??HCFC1??MCEE??SUCLG1??SUCLG2 and ABCD4 genes. Prenatal diagnosis is mainly based on genetic analysis for amniotic fluid cells or chorionic cells. The increased ratio of propionic carnitine/acetylcarnitine??and the increased methylmalonic acid and methyl citric acid in the amniotic fluid from pregnant women can be used as an auxiliary indexes for prenatal diagnosis of this disease. Detection of amniotic fluid homocysteine level can be used as a method for prenatal diagnosis of combined MMA.     

Renal handling of carnitine in children with carnitine deficiency and hyperammonemia associated with valproate therapy

Free and acylcarnitine in serum and urine samples were measured in five patients with hyperammonemia associated with anticonvulsant therapy including sodium valproate, of whom three had a Reye-like syndrome. All had considerable reduction in serum free carnitine and slight increase of acylcarnitine concentrations, suggesting increased conversion of free to acylcarnitine by valproate administration. Urinary excretion of both free and acylcarnitine was increased, accompanied by depressed reabsorption of free carnitine and decreased acylcarnitine/free carnitine clearance ratio. These results indicate a decreased threshold for free carnitine. The combination of these several factors may be responsible for carnitine deficiency in patients with hyperammonemia taking valproate.     

串联质谱技术在遗传性代谢病高危儿童筛查中的初步应用

目的　开展遗传性代谢病高危儿童筛查检测。方法　临床疑诊遗传性代谢病儿童 10 4例 ,男 77例 ,女 2 7例 ,年龄 (4 8± 4 2 )岁。手指采血 ,滴于专用采血滤纸上。干血滤纸片与含已知量的氨基酸、酰基肉碱同位素内标一起 ,经甲醇萃取 ,盐酸正丁醇衍生后 ,用串联质谱仪分析血片中氨基酸谱和酰基肉碱谱及其浓度。结果　在 10 4例标本中 ,检出阳性标本 10例 (9 6 % ) ,其中酪氨酸血症1例 ,同型胱氨酸血症 1例 ,高鸟氨酸血症 1例 ,甲基丙二酸血症 2例 ,丙酸血症 1例 ,3 羟基 3 甲基戊二酸裂解酶缺乏症 1例 ,中链酰基辅酶A脱氢酶缺乏症 2例 ,酰基肉碱转移酶Ⅱ缺乏症 1例。结论串联质谱技术可检测 30余种遗传性代谢病 ,包括氨基酸代谢紊乱、有机酸代谢紊乱和脂肪酸代谢紊乱性疾病 ,高危遗传性代谢病患儿的筛查有重要价值     

Rare disorders of metabolism with elevated butyryl- and isobutyryl-carnitine detected by tandem mass spectrometry newborn screening

Tandem mass spectrometry was adopted for newborn screening by North Carolina in April 1999. Since then, three infants with short-chain acyl-CoA dehydrogenase (SCAD) and one with isobutyryl-CoA dehydrogenase deficiency were detected on the basis of elevated butyrylcarnitine/isobutyrylcarnitine (C4-carnitine) concentrations in newborn blood spots analyzed by tandem mass spectrometry. For three SCAD-deficient infants, biochemical evaluation included a plasma acylcarnitine profile with markedly elevated C4-carnitine, urine organic acid analysis with markedly elevated ethylmalonic and 2-methylsuccinic acids, and markedly elevated [U-13C]butyrylcarnitine concentrations in medium from fibroblasts incubated with [U-13C]palmitic acid and excess l-carnitine, consistent with classic SCAD deficiency. Two of three infants diagnosed with classic SCAD deficiency remained asymptomatic; however, the third infant presented with seizures and a cerebral infarct at 10 wk of age. All three infants had putatively inactivating mutations in both alleles of the SCAD gene. The highly elevated plasma C4-carnitine levels in the three infants detected by newborn screening tandem mass spectrometry differentiated them from infants and children who were homozygous or compound heterozygous for one of two SCAD gene susceptibility variations; for the latter group the C4-carnitine levels were normal. Isobutyryl-CoA dehydrogenase deficiency in a fourth infant was confirmed after isolated elevation of C4-carnitine in the acylcarnitine profile.     

Postmortem screening for fatty acid oxidation disorders by analysis of Guthrie cards with tandem mass spectrometry in sudden unexpected death in infancy

A protocol was developed for the detection of fatty acid oxidation disorders (FOD) in cases of sudden unexpected death in infancy (SUDI). Tandem mass spectrometry blood acylcarnitine analysis of Guthrie card blood spots was performed. In the first 5 years, 1.2% of Oregon's 247 SUDI cases were identified with FOD, 2 with medium-chain acyl-CoA dehydrogenase deficiency, and one with very long-chain acyl-CoA dehydrogenase deficiency.