Short-chain acyl-CoA Dehydrogenase Gene Research Articles

Variants in the ethylmalonyl-CoA decarboxylase (ECHDC1) gene: a novel player in ethylmalonic aciduria?

Ethylmalonic acid (EMA) is a major and potentially cytotoxic metabolite associated with short‐chain acyl‐CoA dehydrogenase (SCAD) deficiency, a condition whose status as a disease is uncertain. Unexplained high EMA is observed in some individuals with complex neurological symptoms, who carry the SCAD gene (ACADS) variants, c.625G>A and c.511C>T. The variants have a high allele frequency in the general population, but are significantly overrepresented in individuals with elevated EMA. This has led to the idea that these variants need to be associated with variants in other genes to cause hyperexcretion of ethylmalonic acid and possibly a diseased state. Ethylmalonyl‐CoA decarboxylase (ECHDC1) has been described and characterized as an EMA metabolite repair enzyme, however, its clinical relevance has never been investigated. In this study, we sequenced the ECHDC1 gene (ECHDC1) in 82 individuals, who were reported with unexplained high EMA levels due to the presence of the common ACADS variants only. Three individuals with ACADS c.625G>A variants were found to be heterozygous for ECHDC1 loss‐of‐function variants. Knockdown experiments of ECHDC1, in healthy human cells with different ACADS c.625G>A genotypes, showed that ECHDC1 haploinsufficiency and homozygosity for the ACADS c.625G>A variant had a synergistic effect on cellular EMA excretion. This study reports the first cases of ECHDC1 gene defects in humans and suggests that ECHDC1 may be involved in elevated EMA excretion in only a small group of individuals with the common ACADS variants. However, a direct link between ECHDC1/ACADS deficiency, EMA and disease could not be proven.

Effects of short-chain acyl-CoA dehydrogenase on human umbilical vein endothelial cell apoptosis

To observe the changes of short-chain acyl-CoA dehydrogenase (SCAD) expression on human umbilical vein endothelial cell (HUVEC) apoptosis and investigate its relationship with apoptosis. The HUVEC was cultured normally for 2-3 days. The apoptotic model of HUVEC was established by tert-butyl hydrogen peroxide (tBHP). The HUVEC was treated by different concentrations of tBHP (0, 10, 20, 30, 40, 50 μmol/L) for 12 hours and different time (0, 3, 6, 9, 12 hours) with 50 μmol/L tBHP to establish the apoptotic model of HUVEC. The cell viability was detected by methyl thiazolyl tetrazolium (MTT), the mRNA expression of SCAD was determined by real-time polymerase chain reaction (PCR), the protein expression of SCAD was achieved by Western Blot. The best concentrate and time were determined to interfere the HUVEC to achieve the apoptotic model of HUVEC. The SCAD gene of HUVEC was knocked down by RNA interference sequence (siRNA274, siRNA414, siRNA679). The mRNA expression of SCAD, the protein expression of SCAD and the activity of SCAD enzyme were detected to achieve the best RNA interference sequence. The HUVEC was intervened by the best RNA interference sequence and tBHP. The cell activity and apoptosis rate, the enzyme activity of SCAD, the mRNA and protein expression of SCAD, the contents of reactive oxygen species (ROS), aderosine triphosphate (ATP) and free fatty acid (FFA) were detected to observe the effect of SCAD on apoptosis of HUVEC. (1) The cell viability, the mRNA expression and the protein expression of SCAD were decreased gradually in a concentration and time dependent manner with the increase of tBHP concentration and the prolongation of intervention time. The decline was most significant in the group of the 50 μmol/L tBHP to interfere HUVEC for 12 hours. (2) The siRNA679 transfection was the most significant in reducing SCAD mRNA and protein expressions among the three interference sequences (siRNA274, siRNA414, siRNA679). (3) Compare with blank control group, the cell viability was significantly decreased in the siRNA679 group (A value: 0.48±0.09 vs. 1.00±0.09, P < 0.01), the apoptotic rate of HUVEC was significantly increased [(29.96±2.09)% vs. (2.90±1.90)%, P < 0.01], the expression of SCAD mRNA and SCAD protein, the activity of SCAD enzyme and the content of ATP were significantly decreased [SCAD mRNA (2-ΔΔCt): 0.50±0.16 vs. 1.34±0.12, SCAD/α-Tubulin: 0.67±0.11 vs. 1.00±0.06, the activity of SCAD enzyme (kU/g): 0.38±0.04 vs. 0.53±0.04, the content of ATP (μmol/g): 0.14±0.02 vs. 0.19±0.01, all P < 0.05], the contents of FFA and ROS were significantly increased [FFA (nmol/g): 0.84±0.07 vs. 0.47±0.04, ROS (average fluorescence intensity): 647.5±23.7 vs. 434.2±46.5, both P < 0.01]. Meanwhile, SCAD siRNA treatment triggered the same apoptosis as HUVEC treated with tBHP. Down-regulation of SCAD may play an important role in HUVEC apoptosis. Increase in the expression of SCAD may become an important part in intervening HUVEC apoptosis.

Metabolic heritability at birth: implications for chronic disease research.

Recent genome-wide association studies of the adult human metabolome have identified genetic variants associated with relative levels of several acylcarnitines, which are important clinical correlates for chronic conditions such as type 2 diabetes and obesity. We have previously shown that these same metabolite levels are highly heritable at birth; however, no studies to our knowledge have examined genetic associations with these metabolites measured at birth. Here, we examine, in 743 newborns, 58 single nucleotide polymorphisms (SNPs) in 11 candidate genes previously associated with differing relative levels of short-chain acylcarnitines in adults. Six SNPs (rs2066938, rs3916, rs3794215, rs555404, rs558314, rs1799958) in the short-chain acyl-CoA dehydrogenase gene (ACADS) were associated with neonatal C4 levels. Most significant was the G allele of rs2066938, which was associated with significantly higher levels of C4 (P = 1.5 × 10(-29)). This SNP explains 25 % of the variation in neonatal C4 levels, which is similar to the variation previously reported in adult C4 levels. There were also significant (P < 1 × 10(-4)) associations between neonatal levels of C5-OH and SNPs in the solute carrier family 22 genes (SLC22A4 and SLC22A5) and the 3-methylcrotonyl-CoA carboxylase 1 gene (MCCC1). We have replicated, in newborns, SNP associations between metabolic traits and the ACADS and SLC22A4 genes observed in adults. This research has important implications not only for the identification of rare inborn errors of metabolism but also for personalized medicine and early detection of later life risks for chronic conditions.

Proteomic investigation of cultivated fibroblasts from patients with mitochondrial short-chain acyl-CoA dehydrogenase deficiency

Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is a rare inherited autosomal recessive disorder with not yet well established mechanisms of disease. In the present study, the mitochondrial proteome of five symptomatic patients homozygous for missense variations in the SCAD gene ACADS was investigated in an extensive large-scale proteomic study to map protein perturbations linked to the disease.Fibroblast cultures of patient cells homozygous for either c.319C>T/p.Arg107Cys (n=2) or c.1138C>T/p.Arg380Trp (n=3) in ACADS, and healthy controls (normal human dermal fibroblasts), were studied. The mitochondrial proteome derived from these cultures was analyzed by label free proteomics using high mass accuracy nanoliquid chromatography tandem mass spectrometry (nanoLC–MS/MS).More than 300 mitochondrial proteins were identified and quantified. Thirteen proteins had significant alteration in protein levels in patients carrying variation c.319C>T in ACADS compared to controls and they belonged to various pathways, such as the antioxidant system and amino acid metabolism. Twenty-two proteins were found significantly altered in patients carrying variation c.1138C>T which included proteins associated with fatty acid β-oxidation, amino acid metabolism and protein quality control system. Three proteins were found significantly regulated in both patient groups: adenylate kinase 4 (AK4), nucleoside diphosphate kinase A (NME1) and aldehyde dehydrogenase family 4 member A1 (ALDH4A1). Proteins AK4 and NME1 deserve further investigation because of their involvement in energy reprogramming, cell survival and proliferation with relevance for SCAD deficiency and related metabolic disorders.

Toxic response caused by a misfolding variant of the mitochondrial protein short-chain acyl-CoA dehydrogenase.

BackgroundVariations in the gene ACADS, encoding the mitochondrial protein short-chain acyl CoA-dehydrogenase (SCAD), have been observed in individuals with clinical symptoms. The phenotype of SCAD deficiency (SCADD) is very heterogeneous, ranging from asymptomatic to severe, without a clear genotype–phenotype correlation, which suggests a multifactorial disorder. The pathophysiological relevance of the genetic variations in the SCAD gene is therefore disputed, and has not yet been elucidated, which is an important step in the investigation of SCADD etiology.AimTo determine whether the disease-associated misfolding variant of SCAD protein, p.Arg107Cys, disturbs mitochondrial function.MethodsWe have developed a cell model system, stably expressing either the SCAD wild-type protein or the misfolding SCAD variant protein, p.Arg107Cys (c.319 C > T). The model system was used for investigation of SCAD with respect to expression, degree of misfolding, and enzymatic SCAD activity. Furthermore, cell proliferation and expression of selected stress response genes were investigated as well as proteomic analysis of mitochondria-enriched extracts in order to study the consequences of p.Arg107Cys protein expression using a global approach.ConclusionsWe found that expression of the p.Arg107Cys variant SCAD protein gives rise to inactive misfolded protein species, eliciting a mild toxic response manifested though a decreased proliferation rate and oxidative stress, as shown by an increased demand for the mitochondrial antioxidant SOD2. In addition, we found markers of apoptotic activity in the p.Arg107Cys expressing cells, which points to a possible pathophysiological role of this variant protein.Electronic supplementary materialThe online version of this article (doi:10.1007/s10545-010-9255-7) contains supplementary material, which is available to authorized users.

Evidence in Colombia of 625G&gt;A polymorphism in the short chain acyl-CoA dehydrogenase gene, a variation which could cause glutaric aciduria in our populations

Introduction: Short-chain acyl-CoA dehydrogenase (SCAD) is a homotetrameric mitochondrial flavoenzyme that catalyzes the initial reaction in short-chain fatty acid b-oxidation. The SCAD gene is located on chromosome 12q22 and is approximately 13 kb long with 10 exons and 1236 nucleotides of coding sequence. Hereditary SCAD deficiency has been reported and only a few cases of this disorder have been described. Objective: The present study was conducted to determine the possible presence of the 625G>A variation in the short-chain acyl-CoA dehydrogenase gene in Caldas (Colombia), given that variations 625G>A and 511C>T are present in 14% of some studied populations; thereby sometimes causing its deficiency. Methods: This is a descriptive study; blood samples from three-hundred adult volunteers were tested for 625G>A polymorphism, analysing the polymerase chain reaction amplified cDNA, using a single-stranded conformation polymorphism assay. The results were confirmed by direct bidirectional cycle sequencing using DNA from the positive persons. Results: The polymorphism was identified and confirmed in four healthy persons. Conclusion: This is evidence of the presence of 625G>A polymorphism in the short-chain acyl-CoA dehydrogenase gene in Colombia, meaning that some people in our populations can be at risk of suffering SCAD deficiency and its main complication: the ethylmalonic aciduria.

Short-chain acyl-CoA dehydrogenase gene mutation (c.319C>T) presents with clinical heterogeneity and is candidate founder mutation in individuals of Ashkenazi Jewish origin

We report 10 children (7 male, 3 female), 3 homozygous for c.319C>T mutation and 7 heterozygous for c.319C>T on one allele and c.625G>A variant on the other in the short-chain acyl-CoA dehydrogenase (SCAD) gene ( ACADS). All were of Ashkenazi Jewish origin in which group we found a c.319C>T heterozygote frequency of 1:15 suggesting the presence of a founder mutation or selective advantage. Phenotype was variable with onset from birth to early childhood. Features included hypotonia (8/10), developmental delay (8/10), myopathy (4/10) with multicore changes in two and lipid storage in one, facial weakness (3/10), lethargy (5/10), feeding difficulties (4/10) and congenital abnormalities (3/7). One female with multiminicore myopathy had progressive external ophthalmoplegia, ptosis and cardiomyopathy with pneumonia and respiratory failure. Two brothers presented with psychosis, pyramidal signs, and multifocal white matter abnormalities on MRI brain suggesting additional genetic factors. Two other infants also had white matter changes. Elevated butyrylcarnitine (4/8), ethylmalonic aciduria (9/9), methylsuccinic aciduria (6/7), decreased butyrate oxidation in lymphoblasts (2/4) and decreased SCAD activity in fibroblasts or muscle (3/3) were shown. Expression studies of c.319C>T in mouse liver mitochondria showed it to be inactivating. c.625G>A is a common variant in ACADS that may confer disease susceptibility. Five healthy parents were heterozygous for c.319C>T and c.625G>A, suggesting reduced penetrance or broad clinical spectrum. We conclude that the c.319C>T mutation can lead to wide clinical and biochemical phenotypic variability, suggesting a complex multifactorial/polygenic condition. This should be screened for in individuals with multicore myopathy, particularly among the Ashkenazim.

Persistent Growth Failure in Prader-Willi Syndrome Associated With Short-Chain Acyl-CoA Dehydrogenase Gene Variant

The authors report the rare association of Prader-Willi syndrome and short-chain acyl-CoA dehydrogenase gene variant. Prader-Willi syndrome, associated with paternal chromosome 15q11-q13 silencing, is characterized by neonatal/infantile hypotonia, growth failure, and neurodevelopmental delays in the first 1 to 2 years of life, typically followed by hyperphagia and obesity. Short-chain acyl-CoA dehydrogenase gene variant, with 625 G-to-A and 511 C-to-T changes, impairs C4-C6 fatty acid metabolism and variably causes neonatal/infantile hypotonia with developmental delays. The authors' patient continues to exhibit the classic severe growth failure of early infancy Prader-Willi syndrome at 40 months. Extensive laboratory investigations indicate that the short-chain acyl-CoA dehydrogenase gene variant is likely preventing or delaying the normal expression of the Prader-Willi syndrome phenotype.

A new case of short-chain acyl-CoA dehydrogenase deficiency: clinical, biochemical, genetic and 1H-NMR spectroscopic studies

Short-chain-acyl-CoA-dehydrogenase (SCAD) deficiency is an inborn error of mitochondrial fatty acid metabolism caused by rare mutations as well as common susceptibility variations in the SCAD gene. We describe the case of a 23-year-old male patient who had growth and mental retardation, recurrent vomiting, fever and seizures since infancy. Urinary gas chromatography and (1)H-nuclear magnetic resonance showed elevated levels of ethylmalonic acid. Serum concentrations of acylcarnitine, especially butyrylcarnitine (C4), were abnormally high. A homozygous variant allele of the SCAD gene, 625G>A, was detected. The patient broadens the clinical phenotype of SCAD deficiency and underlines the difficulty of diagnosis. The limited number of patients described may be the result of underdiagnosis.

REMOVED: Short-chain acyl-CoA dehydrogenase gene mutation (319 C>T) presents with clinical heterogeneity and is candidate founder mutation in Ashkenazi Jewish population

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Short-Chain Acyl-CoA Dehydrogenase Deficiency Associated with Early Onset Severe Axonal Neuropathy

Two unusual cases of axonal neuropathy associated with short-chain acyl-CoA dehydrogenase (SCAD) deficiency are described. These two unrelated infants presented with profound generalised weakness, particularly affecting the upper limbs. Clinical examination revealed generalised peripheral hypotonia and weakness, with absent deep tendon reflexes. An axonal polyneuropathy was confirmed on electromyogram (EMG) and nerve conduction studies (NCS) and, following an extensive metabolic screen, an acylcarnitine and organic acid profile consistent with a short-chain fatty acid beta-oxidation defect was found. In both cases, SCAD deficiency was confirmed by enzyme analysis. Genetic analysis showed the presence of common gene variations in the SCAD gene. SCAD deficiency is a rare disorder with a wide clinical phenotype. SCAD deficiency associated with axonal neuropathy has not previously been reported. As highlighted in these cases, it may be necessary to include axonal neuropathy as a presenting feature of SCAD.

The 625G&gt;A SCAD gene variant is common but not associated with increased C4‐carnitine in newborn blood spots

The 625G>A variant of the short-chain acyl-CoA dehydrogenase (SCAD) gene is considered to confer susceptibility for developing 'clinical SCAD deficiency' and appears to be common in the general population. To determine the frequency of the 625G>A variant in The Netherlands, we analysed 1036 screening cards of 5- to 8-day-old newborns and found 5.5% homozygous and 31.3% heterozygous for the 625G>A variant. An increased blood/plasma C4-carnitine concentration is considered to be one of the biochemical characteristics of SCAD deficiency. To explore the correlation of C4-carnitine levels with the 625G>A variant, we determined the C4-carnitine concentration, as well as the ratio of C4- to free carnitine, in blood spots from newborns, who were detected as homozygous, heterozygous or noncarriers for the gene variant. No significant differences were found between these groups. Our study demonstrates a high frequency of the 625G>A SCAD gene variant in the Dutch population, but no correlation to significantly increased C4-carnitine levels in blood spots taken between the 5th and 8th days of life. This latter observation might be the result of the relatively late timing of neonatal screening in our country, implying that fatty acid oxidation disorders may be missed at that stage. If the 625G>A variant is associated with clinical SCAD deficiency, the high frequency of the variant suggests a possible involvement of SCAD deficiency in the pathogenesis of common disorders, probably in relation to other genetic and/or environmental factors. However, homozygosity for the 625G>A variant might be only a biochemical phenomenon, representing a 'nondisease'.

Misfolding, Degradation, and Aggregation of Variant Proteins: THE MOLECULAR PATHOGENESIS OF SHORT CHAIN ACYL-CoA DEHYDROGENASE (SCAD) DEFICIENCY

Short chain acyl-CoA dehydrogenase (SCAD) deficiency is an inborn error of the mitochondrial fatty acid metabolism caused by rare variations as well as common susceptibility variations in the SCAD gene. Earlier studies have shown that a common variant SCAD protein (R147W) was impaired in folding, and preliminary experiments suggested that the variant protein displayed prolonged association with chaperonins and delayed formation of active enzyme. Accordingly, the molecular pathogenesis of SCAD deficiency may rely on intramitochondrial protein quality control mechanisms, including degradation and aggregation of variant SCAD proteins. In this study we investigated the processing of a set of disease-causing variant SCAD proteins (R22W, G68C, W153R, R359C, and Q341H) and two common variant proteins (R147W and G185S) that lead to reduced SCAD activity. All SCAD proteins, including the wild type, associate with mitochondrial hsp60 chaperonins; however, the variant SCAD proteins remained associated with hsp60 for prolonged periods of time. Biogenesis experiments at two temperatures revealed that some of the variant proteins (R22W, G68C, W153R, and R359C) caused severe misfolding, whereas others (R147W, G185S, and Q341H) exhibited a less severe temperature-sensitive folding defect. Based on the magnitude of in vitro defects, these SCAD proteins are characterized as folding-defective variants and mild folding variants, respectively. Pulse-chase experiments demonstrated that the variant SCAD proteins either triggered proteolytic degradation by mitochondrial proteases or, especially at elevated temperature, aggregation of non-native conformers. The latter finding may indicate that accumulation of aggregated SCAD proteins may play a role in the pathogenesis of SCAD deficiency.

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.

The frequency of short-chain acyl-CoA dehydrogenase gene variants in the US population and correlation with the C 4-acylcarnitine concentration in newborn blood spots

Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is a clinically heterogeneous disorder. The clinical phenotype varies from fatal metabolic decompensation in early life to subtle adult onset, some patients remain asymptomatic. Two mutations (511C > T; 625G > A) have been described in exons 5 and 6 of the SCAD gene. Although they alter the structural and catalytic properties of the SCAD protein, these variants are not true disease-causing mutations but confer disease susceptibility. Previous studies found these gene variants to be common in Europeans. We aimed to establish the frequency of these variants in the US population and to determine whether the presence of these variants correlates with elevated butyrylcarnitine (C 4-acylcarnitine) concentrations in newborn blood spots. Based on the analysis of 694 samples, we found that the allele frequency of the 625G > A variant was significantly higher (22%) than that of the 511C > T variant (3%). These gene variants were detected in either homozygous or compound heterozygous form in 7% of the study population. Additionally, the frequency of the 625G > A allele in the Hispanic population (30%) was significantly higher than that of the African-American (9%) and Asian (13%) subpopulations. A previously unreported variant, IVS 5 (−10) C > T, was identified in three African-American newborns (0.3%). The C 4-acylcarnitine concentration in blood spots was significantly higher in subjects homozygous for the 625A variant when compared to those homozygous for the wild type ( p<0.0001). However, none of the observed genotypes was associated with a concentration of C 4-acylcarnitine that would be consistent with a biochemical diagnosis of SCAD deficiency.

Purification and characterization of two polymorphic variants of short chain acyl-CoA dehydrogenase reveal reduction of catalytic activity and stability of the Gly185Ser enzyme.

Short chain acyl-CoA dehydrogenase (SCAD) is a homotetrameric flavoenzyme that catalyzes the first intramitochondrial step in the beta-oxidation of fatty acids. Two polymorphisms in the coding region of the SCAD gene, 511C>T (R147W) and 625G>A (G185S), have been shown to be associated with an increased level of ethylmalonic acid excretion in urine, a clinical characteristic of SCAD deficiency. To characterize the biochemical consequences of these variations, in vitro site-directed mutagenesis and prokaryotic expression were used to produce the corresponding SCAD variant proteins. Both variant proteins were unstable when produced in Escherichia coli, but could be rescued and subsequently purified by coexpressing them with the bacterial chaperonin GroEL/ES. The k(cat)/K(m) values of the green wild-type, R147W, and G185S SCAD enzymes coexpressed with GroEL/ES were 33, 30, and 10 microM(-)(1) s(-)(1), respectively. There were minimal differences in the kinetic parameters measured for the green, degreened, and wild-type enzymes coexpressed with GroEL/ES, and the R147W variant when butyryl-CoA was used as a substrate. The catalytic efficiency of the G185S variant enzyme, however, was reduced compared to that of the wild-type enzyme. The thermal and guanidine HCl stability of the purified enzymes as determined by fluorescence, far-UV CD spectroscopy, and incubation-induced rest activity showed the following order of relative stability: wild-type enzyme > R147W > G185S. Near-UV CD spectroscopy indicated that these impairments are caused by decreased flexibility in the tertiary conformation of the two mutant enzymes. The common SCAD polymorphisms may lead to clinically relevant alterations in enzyme function.

Hypoglycaemia and elevated urine ethylmalonic acid in a child homozygous for the short‐chain acyl‐CoA dehydrogenase 625G &gt; A gene variation

The aim of this case report is to call attention to short‐chain acyl‐CoA dehydrogenase (SCAD) deficiency as a possible contributory factor to hypoglycaemia in childhood. We report on a previously healthy 14 mo‐old Danish boy who presented with hypoglycaemia and metabolic acidosis after a few days of upper airway infection. After two days on a normal diet, he recovered clinically and biochemically. A thorough biochemical examination did not reveal the cause of the hypoglycaemia. However, the excretion of ethylmalonic acid in two morning urine samples was moderately increased, and hence the SCAD gene was screened for mutations. We found the child homozygous for the G &gt; A SCAD gene variation at position 625. Conclusion: In this patient, reduced function of the SCAD protein is reflected in the excretion of ethylmalonic acid, a marker of intracellular accumulation of butyryl‐CoA and the cytotoxic butyric acid. Furthermore, gluconeogenesis might be compromised owing to lack of reducing equivalents from the oxidation of short‐chain fatty acids in the fasting or stressed state, thus contributing to the predisposition for fasting hypoglycaemia.

Role of common gene variations in the molecular pathogenesis of short-chain acyl-CoA dehydrogenase deficiency.

ABSTRACT Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is considered a rare inherited mitochondrial fatty acid oxidation disorder. Less than 10 patients have been reported, diagnosed on the basis of ethylmalonic aciduria and low SCAD activity in cultured fibroblast. However, mild ethylmalonic aciduria, a biochemical marker of functional SCAD deficiency in vivo, is a common finding in patients suspected of having metabolic disorders. Based on previous observations, we have proposed that ethylmalonic aciduria in a small proportion of cases is caused by pathogenic SCAD gene mutations, and SCAD deficiency can be demonstrated in fibroblasts. Another - much more frequent - group of patients with mild ethylmalonic aciduria has functional SCAD deficiency due to the presence of susceptibility SCAD gene variations, i.e. 625G>A and 511C>T, in whom a variable or moderately reduced SCAD activity in fibroblasts may still be clinically relevant. To substantiate this notion we performed sequence analysis of the SCAD gene in 10 patients with ethylmalonic aciduria and diagnosed with SCAD deficiency in fibroblasts. Surprisingly, only one of the 10 patients carried pathogenic mutations in both alleles, while five were double heterozygotes for a pathogenic mutation in one allele and the 625G>A susceptibility variation in the other. The remaining four patients carried only either the 511C>T or the 625G>A variations in each allele. Our findings document that patients carrying these SCAD gene variations may develop clinically relevant SCAD deficiency, and that patients with even mild ethylmalonic aciduria should be tested for these variations.

Prevalent mutations in fatty acid oxidation disorders: diagnostic considerations.

The mutational spectrum in a given disease-associated gene is often comprised of a large number of different mutations, of which a single or a few are present in a large proportion of diseased individuals. Such prevalent mutations are known in four genes of the fatty acid oxidation: the medium-chain acyl-CoA dehydrogenase (MCAD) gene; the short-chain acyl-CoA dehydrogenase (SCAD) gene; the long-chain 3-hydroxy acyl-CoA dehydrogenase (LCHAD) gene and the carnitine-palmitoyl-CoA transferase II (CPT II) gene. In MCAD deficiency the analysis confirms the conventional wisdom that individuals carrying the prevalent 985A > G mutation are at risk of developing life-threatening attacks. In SCAD/ethylmalonic aciduria, on the other hand, the presence of the prevalent susceptibility variations, 625A and 511T, in the SCAD gene seems to require additional genetic and cellular factors to be present in order to result in a phenotype. For the prevalent mutations in the LCHAD and CPT II genes further data are needed to evaluate the penetrance and risk of manifest disease when carrying these mutations. Assessment of the prevalence of a prevalent mutation in the mutation spectrum of the disease in question and determination of the carrier frequency in the general population may help in elucidating the penetrance of the genotype. This is exemplified in disorders of mitochondrial fatty acid oxidation.

Clinical and biochemical features of fatty acid oxidation disorders.

Inborn errors of fatty acid oxidation (FAO) represent a group of metabolic disorders that has brought forward many interesting developments, as highlighted by the rapid pace of discovery of new defects and by the recognition of an ever-increasing spectrum of clinical phenotypes. This review includes a clinical and biochemical summary of the FAO disorders known to date, a synopsis of four recently discovered defects (short-chain 3-hydroxy acyl-CoA [coenzyme A] dehydrogenase deficiency, medium-chain 3-ketoacyl-CoA thiolase deficiency, 3-hydroxy-3-methylglutaryl-CoA synthase deficiency, and long-chain fatty acid transport deficiency) and of two susceptibility variations in the short-chain acyl-CoA dehydrogenase gene, and guidelines for the biochemical work-up of candidate patients.