Identification of two mutations in a compound heterozygous child with dihydrolipoamide dehydrogenase deficiency

Structural and Biochemical Investigation of Selected Pathogenic Mutants of the Human Dihydrolipoamide Dehydrogenase

Clinically relevant disease-causing variants of the human dihydrolipoamide dehydrogenase (hLADH, hE3), a common component of the mitochondrial α-keto acid dehydrogenase complexes, were characterized using a multipronged approach to unravel the molecular pathomechanisms that underlie hLADH deficiency. The G101del and M326V substitutions both reduced the protein stability and triggered the disassembly of the functional/obligate hLADH homodimer and significant FAD losses, which altogether eventually manifested in a virtually undetectable catalytic activity in both cases. The I12T-hLADH variant proved also to be quite unstable, but managed to retain the dimeric enzyme form; the LADH activity, both in the forward and reverse catalytic directions and the affinity for the prosthetic group FAD were both significantly compromised. None of the above three variants lent themselves to an in-depth structural analysis via X-ray crystallography due to inherent protein instability. Crystal structures at 2.89 and 2.44 Å resolutions were determined for the I318T- and I358T-hLADH variants, respectively; structure analysis revealed minor conformational perturbations, which correlated well with the residual LADH activities, in both cases. For the dimer interface variants G426E-, I445M-, and R447G-hLADH, enzyme activities and FAD loss were determined and compared against the previously published structural data.

Lipoamide dehydrogenase (LADH) deficiency: medical perspectives of the structural and functional characterization of LADH and its pathogenic variants

(Dihydro)lipoamide dehydrogenase (LADH) deficiency is an autosomal recessive genetic metabolic disorder. It generally presents with an onset in the neonatal age and premature death. The clinical picture usually involves metabolic decompensation and lactic acidosis that lead to neurological, cardiological, and/or hepatological outcomes. Severity of the disease is due to the fact that LADH is a common E3 subunit to the pyruvate, alpha-ketoglutarate, alpha-ketoadipate, and branched-chain alpha-keto acid dehydrogenase complexes and is also part of the glycine cleavage system; hence, a loss in LADH activity adversely affects several central metabolic pathways simultaneously. The severe clinical manifestations, however, often do not parallel the LADH activity loss, which implies the existence of auxiliary pathological pathways; stimulated reactive oxygen species (ROS) production as well as dissociation from the relevant multienzyme complexes proved to be auxiliary exacerbating pathomechanisms for selected disease-causing LADH mutations. This review provides an overview on the therapeutic challenges of inherited metabolic diseases, structural and functional characteristics of the mitochondrial alpha-keto acid dehydrogenase complexes, molecular pathogenesis and structural basis of LADH deficiency, and relevant potential future medical perspectives.

The α-Ketoglutarate Dehydrogenase Complex as a Hub of Plasticity in Neurodegeneration and Regeneration

Abnormal glucose metabolism is central to neurodegeneration, and considerable evidence suggests that abnormalities in key enzymes of the tricarboxylic acid (TCA) cycle underlie the metabolic deficits. Significant recent advances in the role of metabolism in cancer provide new insight that facilitates our understanding of the role of metabolism in neurodegeneration. Research indicates that the rate-limiting step of the TCA cycle, the α-ketoglutarate dehydrogenase complex (KGDHC) and its substrate alpha ketoglutarate (KG), serve as a signaling hub that regulates multiple cellular processes: (1) is the rate-limiting step of the TCA cycle, (2) is sensitive to reactive oxygen species (ROS) and produces ROS, (3) determines whether KG is used for energy or synthesis of compounds to support growth, (4) regulates the cellular responses to hypoxia, (5) controls the post-translational modification of hundreds of cell proteins in the mitochondria, cytosol, and nucleus through succinylation, (6) controls critical aspects of transcription, (7) modulates protein signaling within cells, and (8) modulates cellular calcium. The primary focus of this review is to understand how reductions in KGDHC are translated to pathologically important changes that underlie both neurodegeneration and cancer. An understanding of each role is necessary to develop new therapeutic strategies to treat neurodegenerative disease.

Identification of Genes Predicting Poor Response of Trastuzumab in Human Epidermal Growth Factor Receptor 2 Positive Breast Cancer

Objective

To identify trastuzumab-resistant genes predicting drug response and poor prognosis in human epidermal growth factor receptor 2 positive (HER2+) breast cancer.

Methods

Gene expression profiles from the GEO (Gene Expression Omnibus) database were obtained and analyzed. Differentially expressed genes (DEGs) between the pathological complete response (pCR) group and non-pCR group in a trastuzumab neoadjuvant therapy cohort and DEGs between Herceptin-resistant and wild-type cell lines were detected and evaluated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analyses were performed to select the functional hub genes. The hub genes' prognostic power was validated by another trastuzumab adjuvant treatment cohort.

Results

Fifty upregulated overlapping DEGs were identified by analyzing two trastuzumab resistance-related GEO databases. Functional analysis picked out ten hub genes enriched in mitochondrial function and metabolism pathways: ASCL1, CPT2, DLD, ELVOL7, GAMT, NQO1, SLC23A1, SPR, UQCRB, and UQCRQ. These hub genes could distinguish patients with trastuzumab resistance from the sensitive ones. Further survival analysis of hub genes showed that DLD overexpression was significantly associated with an unfavorable prognosis in HER2+ breast cancer patients.

Conclusion

Ten novel trastuzumab resistance-related genes were discovered, of which DLD could be used for trastuzumab response prediction and prognostic prediction in HER2+ breast cancer.

The phenotypic spectrum of dihydrolipoamide dehydrogenase deficiency in Saudi Arabia

Background

Dihydrolipoamide dehydrogenase deficiency (DLDD) is a rare metabolic disorder inherited in an autosomal recessive manner. This heterogeneous disease has a variable clinical presentation, onset, and biochemical markers.

Materials and methods

We retrospectively reviewed the clinical and molecular diagnosis of eight cases with DLDD from four referral centers in Saudi Arabia.

Results

Remarkably, we found hepatic involvement ranging from acute hepatic failure to chronic hepatitis in five patients. In addition, neurological disorders in the form of seizures, developmental delay, ataxia, hypotonia and psychomotor symptoms were found in five patients, two of them with a combination of hepatic and neurological symptoms. In addition, only one patient had recurrent episodes of hypoglycemia. While most patients had the hepatic form of homozygous variant c.685G > T in the DLD gene, one patient was found to have a novel variant c.623C > T that had neurological and hepatic symptoms.

Conclusions

We describe the largest reported DLDD cohort in the Saudi population. Clinical, biochemical, radiological, and molecular characterization was reviewed and no clear genotype-phenotype correlation was found in this cohort.

The Effects of a Ketogenic Diet on Patients with Dihydrolipoamide Dehydrogenase Deficiency

Background: Dihydrolipoamide dehydrogenase (DLD lipoamide dehydrogenase, the E3 subunit of the pyruvate dehydrogenase complex (PDHC)) is the third catalytic enzyme of the PDHC, which converts pyruvate to acetyl-CoA catalyzed with the introduction of acetyl-CoA to the tricyclic acid (TCA) cycle. In humans, PDHC plays an important role in maintaining glycose homeostasis in an aerobic, energy-generating process. Inherited DLD-E3 deficiency, caused by the pathogenic variants in DLD, leads to variable presentations and courses of illness, ranging from myopathy, recurrent episodes of liver disease and vomiting, to Leigh disease and early death. Currently, there is no consensus on treatment guidelines, although one suggested solution is a ketogenic diet (KD). Objective: To describe the use and effects of KD in patients with DLD-E3 deficiency, compared to the standard treatment. Results: Sixteen patients were included. Of these, eight were from a historical cohort, and of the other eight, four were on a partial KD. All patients were homozygous for the D479V (or D444V, which corresponds to the mutated mature protein without the mitochondrial targeting sequence) pathogenic variant in DLD. The treatment with partial KD was found to improve patient survival. However, compared to a historical cohort, the patients’ quality of life (QOL) was not significantly improved. Conclusions: The use of KD offers an advantage regarding survival; however, there is no significant improvement in QOL.

Underlying molecular alterations in human dihydrolipoamide dehydrogenase deficiency revealed by structural analyses of disease-causing enzyme variants

Human dihydrolipoamide dehydrogenase (hLADH, hE3) deficiency (OMIM# 246900) is an often prematurely lethal genetic disease usually caused by inactive or partially inactive hE3 variants. Here we report the crystal structure of wild-type hE3 at an unprecedented high resolution of 1.75 Å and the structures of six disease-causing hE3 variants at resolutions ranging from 1.44 to 2.34 Å. P453L proved to be the most deleterious substitution in structure as aberrations extensively compromised the active site. The most prevalent G194C-hE3 variant primarily exhibited structural alterations close to the substitution site, whereas the nearby cofactor-binding residues were left unperturbed. The G426E substitution mainly interfered with the local charge distribution introducing dynamics to the substitution site in the dimer interface; G194C and G426E both led to minor structural changes. The R460G, R447G and I445M substitutions all perturbed a solvent accessible channel, the so-called H+/H2O channel, leading to the active site. Molecular pathomechanisms of enhanced reactive oxygen species (ROS) generation and impaired binding to multienzyme complexes were also addressed according to the structural data for the relevant mutations. In summary, we present here for the first time a comprehensive study that links three-dimensional structures of disease-causing hE3 variants to residual hLADH activities, altered capacities for ROS generation, compromised affinities for multienzyme complexes and eventually clinical symptoms. Our results may serve as useful starting points for future therapeutic intervention approaches.

An Updated View on the Molecular Pathomechanisms of Human Dihydrolipoamide Dehydrogenase Deficiency in Light of Novel Crystallographic Evidence

Dihydrolipoamide dehydrogenase (LADH, E3) deficiency is a rare (autosomal, recessive) genetic disorder generally presenting with an onset in the neonatal age and early death; the highest carrier rate has been found among Ashkenazi Jews. Acute clinical episodes usually involve severe metabolic decompensation and lactate acidosis that result in neurological, cardiological, and/or hepatological manifestations. Clinical severity is due to the fact that LADH is a common E3 subunit to the alpha-ketoglutarate, pyruvate, alpha-ketoadipate, and branched-chain alpha-keto acid dehydrogenase complexes, and is also a constituent in the glycine cleavage system, thus a loss in LADH function adversely affects multiple key metabolic routes. However, the severe clinical pictures frequently still do not parallel the LADH activity loss, which implies the involvement of auxiliary biochemical mechanisms; enhanced reactive oxygen species generation as well as affinity loss for multienzyme complexes proved to be key auxiliary exacerbating pathomechanisms. This review provides an overview and an up-to-date molecular insight into the pathomechanisms of this disease in light of the structural conclusions drawn from the first crystal structure of a disease-causing hE3 variant determined recently in our laboratory.

Human dihydrolipoamide dehydrogenase (E3) deficiency: Novel insights into the structural basis and molecular pathomechanism

This review summarizes our present view on the molecular pathogenesis of human (h) E3-deficiency caused by a variety of genetic alterations with a special emphasis on the moonlighting biochemical phenomena related to the affected (dihydro)lipoamide dehydrogenase (LADH, E3, gene: dld), in particular the generation of reactive oxygen species (ROS). E3-deficiency is a rare autosomal recessive genetic disorder frequently presenting with a neonatal onset and premature death; the highest carrier rate of a single pathogenic dld mutation (1:94-1:110) was found among Ashkenazi Jews. Patients usually die during acute episodes that generally involve severe metabolic decompensation and lactic acidosis leading to neurological, cardiological, and/or hepatological manifestations. The disease owes its severity to the fact that LADH is the common E3 subunit of the alpha-ketoglutarate (KGDHc), pyruvate (PDHc), and branched-chain α-keto acid dehydrogenase complexes and is also part of the glycine cleavage system, hence the malfunctioning of LADH simultaneously incapacitates several central metabolic pathways. Nevertheless, the clinical pictures are usually not unequivocally portrayed through the loss of LADH activities and imply auxiliary mechanisms that exacerbate the symptoms and outcomes of this disorder. Enhanced ROS generation by disease-causing hE3 variants as well as by the E1-E2 subcomplex of the hKGDHc likely contributes to selected pathogeneses of E3-deficiency, which could be targeted by specific drugs or antioxidants; lipoic acid was demonstrated to be a potent inhibitor of ROS generation by hE3 in vitro. Flavin supplementation might prove to be beneficial for those mutations triggering FAD loss in the hE3 component. Selected pathogenic hE3 variants lose their affinity for the E2 component of the hPDHc, a mechanism which warrants scrutiny also for other E3-haboring complexes.

Structural alterations induced by ten disease-causing mutations of human dihydrolipoamide dehydrogenase analyzed by hydrogen/deuterium-exchange mass spectrometry: Implications for the structural basis of E3 deficiency

Pathogenic amino acid substitutions of the common E3 component (hE3) of the human alpha-ketoglutarate dehydrogenase and the pyruvate dehydrogenase complexes lead to severe metabolic diseases (E3 deficiency), which usually manifest themselves in cardiological and/or neurological symptoms and often cause premature death. To date, 14 disease-causing amino acid substitutions of the hE3 component have been reported in the clinical literature. None of the pathogenic protein variants has lent itself to high-resolution structure elucidation by X-ray or NMR. Hence, the structural alterations of the hE3 protein caused by the disease-causing mutations and leading to dysfunction, including the enhanced generation of reactive oxygen species by selected disease-causing variants, could only be speculated. Here we report results of an examination of the effects on the protein structure of ten pathogenic mutations of hE3 using hydrogen/deuterium-exchange mass spectrometry (HDX-MS), a new and state-of-the-art approach of solution structure elucidation. On the basis of the results, putative structural and mechanistic conclusions were drawn regarding the molecular pathogenesis of each disease-causing hE3 mutation addressed in this study.

Interstitial deletion of 7q22.1q31.1 in a boy with structural brain abnormality, cardiac defect, developmental delay, and dysmorphic features

This report describes a male child with a history of poor feeding and swallowing problems, hypotonia, mild bilateral sensorineural hearing loss, cerebral cortical agenesis, cardiac defects, cyanotic episodes triggered by specific movement, dysmorphic features, and developmental delays. Analysis by CytoScan HD array identified a 12.1 Mb interstitial deletion of 7q22.1q31.1 (98,779,628-110,868,171). We present a comprehensive review of the literature surrounding intermediate 7q deletions that overlap with this child's deletion, and an analysis of candidate genes in the deleted region. © 2016 Wiley Periodicals, Inc.

HEPNet: A Knowledge Base Model of Human Energy Pool Network for Predicting the Energy Availability Status of an Individual

HEPNet is an electronic representation of metabolic reactions occurring within human cellular organization focusing on inflow and outflow of the energy currency ATP, GTP and other energy associated moieties. The backbone of HEPNet consists of primary bio-molecules such as carbohydrates, proteins and fats which ultimately constitute the chief source for the synthesis and obliteration of energy currencies in a cell. A series of biochemical pathways and reactions constituting the catabolism and anabolism of various metabolites are portrayed through cellular compartmentalization. The depicted pathways function synchronously toward an overarching goal of producing ATP and other energy associated moieties to bring into play a variety of cellular functions. HEPNet is manually curated with raw data from experiments and is also connected to KEGG and Reactome databases. This model has been validated by simulating it with physiological states like fasting, starvation, exercise and disease conditions like glycaemia, uremia and dihydrolipoamide dehydrogenase deficiency (DLDD). The results clearly indicate that ATP is the master regulator under different metabolic conditions and physiological states. The results also highlight that energy currencies play a minor role. However, the moiety creatine phosphate has a unique character, since it is a ready-made source of phosphoryl groups for the rapid synthesis of ATP from ADP. HEPNet provides a framework for further expanding the network diverse age groups of both the sexes, followed by the understanding of energetics in more complex metabolic pathways that are related to human disorders.

A founder mutation in PET100 causes isolated complex IV deficiency in Lebanese individuals with Leigh syndrome

Leigh syndrome (LS) is a severe neurodegenerative disorder with characteristic bilateral lesions, typically in the brainstem and basal ganglia. It usually presents in infancy and is genetically heterogeneous, but most individuals with mitochondrial complex IV (or cytochrome c oxidase) deficiency have mutations in the biogenesis factor SURF1. We studied eight complex IV-deficient LS individuals from six families of Lebanese origin. They differed from individuals with SURF1 mutations in having seizures as a prominent feature. Complementation analysis suggested they had mutation(s) in the same gene but targeted massively parallel sequencing (MPS) of 1,034 genes encoding known mitochondrial proteins failed to identify a likely candidate. Linkage and haplotype analyses mapped the location of the gene to chromosome 19 and targeted MPS of the linkage region identified a homozygous c.3G>C (p.Met1?) mutation in C19orf79. Abolishing the initiation codon could potentially still allow initiation at a downstream methionine residue but we showed that this would not result in a functional protein. We confirmed that mutation of this gene was causative by lentiviral-mediated phenotypic correction. C19orf79 was recently renamed PET100 and predicted to encode a complex IV biogenesis factor. We showed that it is located in the mitochondrial inner membrane and forms a ∼300 kDa subcomplex with complex IV subunits. Previous proteomic analyses of mitochondria had overlooked PET100 because its small size was below the cutoff for annotating bona fide proteins. The mutation was estimated to have arisen at least 520 years ago, explaining how the families could have different religions and different geographic origins within Lebanon.

Molecular dynamics study of the structural basis of dysfunction and the modulation of reactive oxygen species generation by pathogenic mutants of human dihydrolipoamide dehydrogenase

Human dihydrolipoamide dehydrogenase (LADH, E3) is a component in the pyruvate-, alpha-ketoglutarate- and branched-chain ketoacid dehydrogenase complexes and in the glycine cleavage system. The pathogenic mutations of LADH cause severe metabolic disturbances, called E3 deficiency that often involve cardiological and neurological symptoms and premature death. Our laboratory has recently shown that some of the known pathogenic mutations augment the reactive oxygen species (ROS) generation capacity of LADH, which may contribute to the clinical presentations. A recent report concluded that elevated oxidative stress generated by the above mutants turns the lipoic acid cofactor on the E2 subunits dysfunctional. In the present contribution we generated by molecular dynamics (MD) simulation the conformation of LADH that is proposed to be compatible with ROS generation. We propose here for the first time the structural changes, which are likely to turn the physiological LADH conformation to its ROS-generating conformation. We also created nine of the pathogenic mutants of the ROS-generating conformation and again used MD simulation to detect structural changes that the mutations induced in this LADH conformation. We propose the structural changes that may lead to the modulation in ROS generation of LADH by the pathogenic mutations.

Leigh syndrome in a girl with a novel DLD mutation causing E3 deficiency

We present the biochemical and molecular diagnosis of dihydrolipoamide dehydrogenase deficiency (also known as E3 deficiency) and Leigh syndrome in a 14-year-old girl with learning disability and episodic encephalopathy and ketoacidosis. The diagnosis was based on values of plasma amino acids and urine organic acids, obtained during acute encephalopathy, lactic ketoacidosis, and liver failure, precipitated by infectious mononucleosis. Enzymatic and molecular analyses confirmed dihydrolipoamide dehydrogenase deficiency. E3 activity from cultured skin fibroblasts ranged from 9-29% of the mean. Molecular analysis revealed compound heterozygosity for novel and known pathogenic mutations (p.I353T and p.G136del, respectively). The patient received dietary augmentation and continuous renal replacement therapy, given her severe, persistent lactic acidosis. Acute decompensation resulted in magnetic resonance imaging changes involving the posterior aspect of the putamen, lateral, and medial thalami, substantia nigra, lateral geniculate bodies, and splenium of the corpus callosum. The cortex and subcortical white matter of the right and left occipital lobes and perirolandic region were also affected. In our review of molecularly confirmed patients with dihydrolipoamide dehydrogenase deficiency, Leigh syndrome was common. Our patient, whose most severe decompensation occurred at a more advanced age than previously reported, provides further evidence of the heterogeneous presentations of dihydrolipoamide dehydrogenase deficiency.

The spectrum of pyruvate dehydrogenase complex deficiency: clinical, biochemical and genetic features in 371 patients

CONTEXT

Pyruvate dehydrogenase complex (PDC) deficiency is a genetic mitochondrial disorder commonly associated with lactic acidosis, progressive neurological and neuromuscular degeneration and, usually, death during childhood. There has been no recent comprehensive analysis of the natural history and clinical course of this disease.

OBJECTIVE

We reviewed 371 cases of PDC deficiency, published between 1970 and 2010, that involved defects in subunits E1α and E1β and components E1, E2, E3 and the E3 binding protein of the complex.

DATA SOURCES AND EXTRACTION

English language peer-reviewed publications were identified, primarily by using PubMed and Google Scholar search engines.

RESULTS

Neurodevelopmental delay and hypotonia were the commonest clinical signs of PDC deficiency. Structural brain abnormalities frequently included ventriculomegaly, dysgenesis of the corpus callosum and neuroimaging findings typical of Leigh syndrome. Neither gender nor any clinical or neuroimaging feature differentiated the various biochemical etiologies of the disease. Patients who died were younger, presented clinically earlier and had higher blood lactate levels and lower residual enzyme activities than subjects who were still alive at the time of reporting. Survival bore no relationship to the underlying biochemical or genetic abnormality or to gender.

CONCLUSIONS

Although the clinical spectrum of PDC deficiency is broad, the dominant clinical phenotype includes presentation during the first year of life; neurological and neuromuscular degeneration; structural lesions revealed by neuroimaging; lactic acidosis and a blood lactate:pyruvate ratio ≤ 20.

The spectrum of pyruvate dehydrogenase complex deficiency: clinical, biochemical and genetic features in 371 patients

CONTEXT

Pyruvate dehydrogenase complex (PDC) deficiency is a genetic mitochondrial disorder commonly associated with lactic acidosis, progressive neurological and neuromuscular degeneration and, usually, death during childhood. There has been no recent comprehensive analysis of the natural history and clinical course of this disease.

OBJECTIVE

We reviewed 371 cases of PDC deficiency, published between 1970 and 2010, that involved defects in subunits E1α and E1β and components E1, E2, E3 and the E3 binding protein of the complex.

DATA SOURCES AND EXTRACTION

English language peer-reviewed publications were identified, primarily by using PubMed and Google Scholar search engines.

RESULTS

Neurodevelopmental delay and hypotonia were the commonest clinical signs of PDC deficiency. Structural brain abnormalities frequently included ventriculomegaly, dysgenesis of the corpus callosum and neuroimaging findings typical of Leigh syndrome. Neither gender nor any clinical or neuroimaging feature differentiated the various biochemical etiologies of the disease. Patients who died were younger, presented clinically earlier and had higher blood lactate levels and lower residual enzyme activities than subjects who were still alive at the time of reporting. Survival bore no relationship to the underlying biochemical or genetic abnormality or to gender.

CONCLUSIONS

Although the clinical spectrum of PDC deficiency is broad, the dominant clinical phenotype includes presentation during the first year of life; neurological and neuromuscular degeneration; structural lesions revealed by neuroimaging; lactic acidosis and a blood lactate:pyruvate ratio ≤20.

Mutations in the dimer interface of dihydrolipoamide dehydrogenase promote site-specific oxidative damages in yeast and human cells

Dihydrolipoamide dehydrogenase (DLD) is a multifunctional protein well characterized as the E3 component of the pyruvate dehydrogenase and α-ketoglutarate dehydrogenase complexes. Previously, conditions predicted to destabilize the DLD dimer revealed that DLD could also function as a diaphorase and serine protease. However, the relevance of these cryptic activities remained undefined. We analyzed human DLD mutations linked to strikingly different clinical phenotypes, including E340K, D444V, R447G, and R460G in the dimer interface domain that are responsible for severe multisystem disorders of infancy and G194C in the NAD(+)-binding domain that is typically associated with milder presentations. In vitro, all of these mutations decreased to various degrees dihydrolipoamide dehydrogenase activity, whereas dimer interface mutations also enhanced proteolytic and/or diaphorase activity. Human DLD proteins carrying each individual mutation complemented fully the respiratory-deficient phenotype of yeast cells lacking endogenous DLD even when residual dihydrolipoamide dehydrogenase activity was as low as 21% of controls. However, under elevated oxidative stress, expression of DLD proteins with dimer interface mutations greatly accelerated the loss of respiratory function, resulting from enhanced oxidative damage to the lipoic acid cofactor of pyruvate dehydrogenase and α-ketoglutarate dehydrogenase and other mitochondrial targets. This effect was not observed with the G194C mutation or a mutation that disrupts the proteolytic active site of DLD. As in yeast, lipoic acid cofactor was damaged in human D444V-homozygous fibroblasts after exposure to oxidative stress. We conclude that the cryptic activities of DLD promote oxidative damage to neighboring molecules and thus contribute to the clinical severity of DLD mutations.

Stimulation of reactive oxygen species generation by disease-causing mutations of lipoamide dehydrogenase

We investigated pathogenic mutations relevant in dihydrolipoamide dehydrogenase (LADH; gene: Dld) deficiency, a severe human disease, to elucidate how they alter reactive oxygen species (ROS) generation and associated biophysical characteristics of LADH. Twelve known disease-causing mutants of human LADH have been expressed and purified to homogeneity from E. coli. Detailed biophysical and biochemical characterization of the mutants has been performed applying circular dichroism (CD) spectroscopy, nano-spray mass spectrometry (MS), calibrated gel filtration and flavin adenine dinucleotide-content analysis. Functional analyses revealed that four of the pathogenic mutations significantly stimulated the ROS-generating activity of LADH and also increased its sensitivity to an acidic shift in pH. LADH activity was reduced by variable extents in the mutants exhibiting excessive ROS generation. It is remarkable that in the P453L mutant, enzyme activity was nearly completely lost with a ROS-forming activity becoming dominant, whereas the G194C mutation, common among Ashkenazi Jews, resulted in no alteration in LADH activity but a gain in the ROS-generating activity. There have been neither major conformational alterations nor monomerization of the functional homodimer of LADH associated with the higher ROS-generating capacity as measured by CD spectroscopy and size-exclusion chromatography combined with nano-spray MS, respectively. The excessive ROS generation of selected LADH mutants could be an important factor in the pathology and clinical presentation of human LADH deficiency and raises the possibility of an antioxidant therapy in the treatment of this condition.

Dihydrolipoamide dehydrogenase (DLD) deficiency in a Spanish patient with myopathic presentation due to a new mutation in the interface domain

We present a 32-year-old patient who, from age 7 months, developed photophobia, left-eye ptosis and progressive muscular weakness. At age 7 years, she showed normal psychomotor development, bilateral ptosis and exercise-induced weakness with severe acidosis. Basal blood and urine lactate were normal, increasing dramatically after effort. PDHc deficiency was demonstrated in muscle and fibroblasts without detectable PDHA1 mutations. Ketogenic diet was ineffective, however thiamine gave good response although bilateral ptosis and weakness with acidosis on exercise persisted. Recently, DLD gene analysis revealed a homozygous missense mutation, c.1440 A>G (p.I480M), in the interface domain. Both parents are heterozygous and DLD activity in the patient's fibroblasts is undetectable. The five patients that have been reported with DLD-interface mutations suffered fatal deteriorations. Our patient's disease is milder, only myopathic, more similar to that due to mutation p.G229C in the NAD(+)-binding domain. Two of the five patients presented mutations (p.D479V and p.R482G) very close to the present case (p.I480M). Despite differing degrees of clinical severity, all three had minimal clues to DLD deficiency, with occasional minor increases in α-ketoglutarate and branched-chain amino acids. In the two other patients, hypertrophic cardiomyopathy was a significant feature that has been attributed to moonlighting proteolytic activity of monomeric DLD, which can degrade other mitochondrial proteins, such as frataxin. Our patient does not have cardiomyopathy, suggesting that p.I480M may not affect the DLD ability to dimerize to the same extent as p.D479V and p.R482G. Our patient, with a novel mutation in the DLD interface and mild clinical symptoms, further broadens the spectrum of this enzyme defect.

Interaction of E1 and E3 components with the core proteins of the human pyruvate dehydrogenase complex

The human (h) pyruvate dehydrogenase complex (hPDC) consists of multiple copies of several components: pyruvate dehydrogenase (E1), dihydrolipoamide acetyltransferase (E2), dihydrolipoamide dehydrogenase (E3), E3-binding protein (BP), and specific kinases and phosphatases. Mammalian PDC has a well organized structure with an icosahedral symmetry of the central E2/BP core to which the other component proteins bind non-covalently. Both hE2 and hBP consist of three well defined domains, namely the lipoyl domain, the subunit-binding domain and the inner domain, connected with flexible linkers. hE1 (alpha(2)beta(2)) binds to the subunit-binding domain of hE2; whereas hE3 binds to the E3-binding domain of hBP. Among several residues of the C-terminal surface of the hE1beta E1betaD289 was found to interact with hE2K276. The C-terminal residue I329 of the hE1beta did not participate in binding to hE2. This latter finding shows specificity in the interaction between E1beta and E2 in hPDC. The selective binding between hE3 and the E3-binding domain of hBP was investigated using specific mutants. E3R460G and E3340K showed significant reductions in affinity for hBP as determined by surface plasmon resonance. Both residues are involved in the structural organization of the binding site on hE3. Substitution of I157, N137 and R155 of hBP resulted in variable increases in the K(D) for binding with wild-type hE3, suggesting that the binding results from several weak electrostatic bonds and hydrophobic interactions among residues of hBP with residues at the interface of dimeric hE3. These results provide insight in the mono-specificity of binding of E1 to E2 and E3 to BP in hPDC and showed the differences in the binding of peripheral components (E1 and E3) in human and bacterial PDCs.

Maternal enzyme masks the phenotype of mouse embryos lacking dihydrolipoamide dehydrogenase

During early embryogenesis, the phenotype reflecting the embryonic genotype emerges only as maternal proteins are replaced by embryonically encoded forms, a process known as the maternal-to-embryonic transition (MET). Little is understood about MET for most proteins. This study investigates how complete deficiency of the murine dihydrolipoamide dehydrogenase gene (Dld), a gene that encodes an enzyme of mitochondrial energy metabolism, affects the phenotype of the early embryo and how the MET of the DLD protein affects the phenotype. Dld-deficient (-/-) embryos were found to develop similarly to wild-type (+/+) or heterozygous (+/-) embryos throughout the preimplantation period. These three genotypic classes also have comparable rates of glucose uptake (4.9-5.0 pmoles/embryo/h) and lactate production (0.97-1.0 pmoles/embryo/h). Dld-deficient embryos at the end of the preimplantation stage have 44% of DLD enzyme present in oocytes, a proportion similar to that found in +/+ or +/- embryos. This study demonstrates that Dld-deficient preimplantation embryos are phenotypically normal, as the MET for the DLD enzyme is only partially complete by the end of the preimplantation period. These findings have implications for phenotype- or enzyme-based approaches to identify mutations in Dld and other genes that encode proteins with similar MET kinetic profiles.

The role of amino acids T148 and R281 in human dihydrolipoamide dehydrogenase

Human dihydrolipoamide dehydrogenase (hE3) is a common component of alpha-ketoacid dehydrogenase complexes. Mutations of this homodimeric protein cause E3 deficiency and are always fatal. To investigate its reaction mechanism, we first performed multiple sequence alignment with other 17 eukaryotic E3s. According to hE3 structure and the result of multiple sequence alignment, two amino acids, T148 and R281, were subjected to mutagenesis and four hE3 mutants, T148G, T148S, R281N, and R281K, were expressed and assayed. The specific activities of T148G, T148S, R281N, and R281K are 76.34%, 88.62%, 12.50%, and 11.93% to that of wild-type E3, respectively. The FAD content analysis indicated that the FAD content of these mutant E3s were about 71.0%, 92%, 96%, and 93% that of wild-type E3, respectively. The molecular weight analysis showed that these three mutant proteins form the dimer. Kinetic data demonstrated that the K(cat) of forward reaction of all mutants, except T148 mutants, were decreased dramatically. The results of kinetic study suggest that T148 is not important to E3 catalytic function and R281 play a role in the catalytic function of the E3.

Testing for linkage and association across the dihydrolipoyl dehydrogenase gene region with Alzheimer's disease in three sample populations

Prior case-control studies from our laboratory of a population enriched with individuals of Ashkenazi Jewish descent suggested that association exists between Alzheimer's disease (AD) and the chromosomal region near the DLD gene, which encodes the mitochondrial dihydrolipoamide dehydrogenase enzyme. In support of this finding, we found that linkage analysis restricted to autopsy-proven patients in the National Institute of Mental Health-National Cell Repository for Alzheimer's Disease (NIMH-NCRAD) Genetics Initiative pedigree data resulted in point-wise significant evidence for linkage (minimum p-value = 0.024) for a marker position close to the DLD locus. We now report case-control replication studies in two independent Caucasian series from the US and Italy, as well as a linkage analysis from the NIMH-NCRAD Genetics Initiative Database. Pair-wise analysis of the SNPs in the case-control series indicated there was strong linkage disequilibrium across the DLD locus in these populations, as previously reported. These findings suggest that testing for association of complex diseases with DLD locus should have considerable statistical power. Analysis of multi-locus genotypes or haplotypes based upon three SNP loci combined with results from our previous report provided trends toward significant evidence of association of DLD with AD, although neither of the present studies' association showed significance at the 0.05 level. Combining linkage and association findings for all AD patients (males and females) results in a p-value that is more significant than any of the individual findings' p-values. Finally, minimum sample size calculations using parameters from the DLD locus suggest that sample sizes on the order of 1,000 total cases and controls are needed to detect association for a wide range of genetic model parameters.

Novel mutations in dihydrolipoamide dehydrogenase deficiency in two cousins with borderline-normal PDH complex activity

We have diagnosed dihydrolipoamide dehydrogenase (DLD) deficiency in two male second cousins, who presented with markedly different clinical phenotypes. Patient 1 had a recurrent encephalopathy, and patient 2 had microcephaly and lactic acidosis. Their presentation is unusual, in that the DLD subunit deficiency had little effect on pyruvate dehydrogenase complex activity, but caused a severe reduction in the activities of other enzymes that utilize this subunit. We have identified two mutations in the DLD gene in each patient. The second cousins have one novel mutation in common resulting in a substitution of isoleucine for threonine (I47T), which has not been previously reported in the literature. Patient 1 has a second mutation that has been reported to be common in the Ashkenazi Jewish population, G229C. Patient 2 has a second mutation, E375K, which has also been previously reported in the literature. Enzyme kinetic measurements on patient fibroblasts show that under certain conditions, one heteroallelic mutation may have a higher K(m). This may account for the differing clinical phenotypes. These findings have important repercussions for other patients with similar clinical phenotypes, as DLD activity is not normally measured in cases with normal PDHc activity.

Comprehensive mutation analysis ofGLDC,AMT, andGCSHin nonketotic hyperglycinemia

Nonketotic hyperglycinemia (NKH) is an inborn error of metabolism characterized by accumulation of glycine in body fluids and various neurological symptoms. NKH is caused by deficiency of the glycine cleavage multi-enzyme system with three specific components encoded by GLDC, AMT, and GCSH. We undertook the first comprehensive screening for GLDC, AMT, and GCSH mutations in 69 families (56, six, and seven families with neonatal, infantile, and late-onset type NKH, respectively). GLDC or AMT mutations were identified in 75% of neonatal and 83% of infantile families, but not in late-onset type NKH. No GCSH mutation was identified in this study. GLDC mutations were identified in 36 families, and AMT mutations were detected in 11 families. In 16 of the 36 families with GLDC mutations, mutations were identified in only one allele despite sequencing of the entire coding regions. The GLDC gene consists of 25 exons. Seven of the 32 GLDC missense mutations were clustered in exon 19, which encodes the cofactor-binding site Lys754. A large deletion involving exon 1 of the GLDC gene was found in Caucasian, Oriental, and black families. Multiple origins of the exon 1 deletion were suggested by haplotype analysis with four GLDC polymorphisms. This study provides a comprehensive picture of the genetic background of NKH as it is known to date.

Structural insight into interactions between dihydrolipoamide dehydrogenase (E3) and E3 binding protein of human pyruvate dehydrogenase complex

The 9.5 MDa human pyruvate dehydrogenase complex (PDC) utilizes the specific dihydrolipoamide dehydrogenase (E3) binding protein (E3BP) to tether the essential E3 component to the 60-meric core of the complex. Here, we report crystal structures of the binding domain (E3BD) of human E3BP alone and in complex with human E3 at 1.6 angstroms and 2.2 angstroms, respectively. The latter structure shows that residues from E3BD contact E3 across its 2-fold axis, resulting in one E3BD binding site on the E3 homodimer. Negligible conformational changes occur in E3BD upon its high-affinity binding to E3. Modifications of E3BD residues at the center of the E3BD/E3 interface impede E3 binding far more severely than those of residues on the periphery, validating the "hot spot" paradigm for protein interactions. A cluster of disease-causing E3 mutations located near the center of the E3BD/E3 interface prevents the efficient recruitment of these E3 variants by E3BP into the PDC, leading to the dysfunction of the PDC catalytic machine.

Crystal structure of human dihydrolipoamide dehydrogenase: NAD+/NADH binding and the structural basis of disease-causing mutations

Human dihydrolipoamide dehydrogenase (hE3) is an enzymatic component common to the mitochondrial alpha-ketoacid dehydrogenase and glycine decarboxylase complexes. Mutations to this homodimeric flavoprotein cause the often-fatal human disease known as E3 deficiency. To catalyze the oxidation of dihydrolipoamide, hE3 uses two molecules: non-covalently bound FAD and a transiently bound substrate, NAD+. To address the catalytic mechanism of hE3 and the structural basis for E3 deficiency, the crystal structures of hE3 in the presence of NAD+ or NADH have been determined at resolutions of 2.5A and 2.1A, respectively. Although the overall fold of the enzyme is similar to that of yeast E3, these two structures differ at two loops that protrude from the proteins and at their FAD-binding sites. The structure of oxidized hE3 with NAD+ bound demonstrates that the nicotinamide moiety is not proximal to the FAD. When NADH is present, however, the nicotinamide base stacks directly on the isoalloxazine ring system of the FAD. This is the first time that this mechanistically requisite conformation of NAD+ or NADH has been observed in E3 from any species. Because E3 structures were previously available only from unicellular organisms, speculations regarding the molecular mechanisms of E3 deficiency were based on homology models. The current hE3 structures show directly that the disease-causing mutations occur at three locations in the human enzyme: the dimer interface, the active site, and the FAD and NAD(+)-binding sites. The mechanisms by which these mutations impede the function of hE3 are discussed.

Association of the dihydrolipoamide dehydrogenase gene with Alzheimer's disease in an Ashkenazi Jewish population

Abundant biochemical evidence links deficient activity of mitochondrial alpha-ketoglutarate dehydrogenase with neuropathologically confirmed Alzheimer's disease (AD). Reduced alpha-ketoglutarate dehydrogenase activity has also been associated with anti-mortem measures of clinical disability. One of the genes encoding this complex, namely, DLD, lies within a chromosome 7 region that is in linkage disequilibrium with AD. We therefore examined the hypothesis that variation in DLD is associated with AD risk. Denaturing HPLC was used to search for sequence variations in the coding and flanking regions of all exons of DLD, but no abundant variants that alter protein sequence were found. However, four common SNPs were identified and genotyped in a case-control series of 297 Caucasians from New York City, including 229 residents of a Jewish nursing home. Logistic regression analysis was performed for the four-locus DLD genotype, sex, and ApoE4 status to determine the association of these independent variables with AD. Significant associations with AD were observed for ApoE4 (P < 10(-6)) and sex combined with DLD genotype (P = 0.013). The association with the DLD genotypes appears only in the male population in both the Caucasian series (P = 0.0009, n = 83) and the Ashkenazi Jewish subseries (P = 0.017, n = 49). The DLD genotype appears to operate independently of APOE in conferring AD risk.

Glucose/mitochondria in neurological conditions

Impairments of glucose and mitochondrial function are important causes of brain dysfunction and therefore of brain disease. Abnormalities have been found in association with disease of the nervous system in most of the components of glucose/mitochondrial metabolism. In many, molecular genetic abnormalities have been defined. Brain glucose oxidation is abnormal in common diseases of the nervous system, including Alzheimer disease and other dementias, Parkinson disease, delirium, probably schizophrenia and other psychoses, and of course cerebrovascular disease. Defects in a single component and even a single mutation can be associated with different clinical phenotypes. The same clinical phenotype can result from different genotypes. The complex relationship between biological abnormality in brain glucose utilization and clinical disorder is similar to that in other disorders that have been intensively studied at the genetic level. Genes for components of the pathways of brain glucose oxidation are good candidate genes for disease of the brain. Preliminary data support the proposal that treatments to normalize abnormalities in brain glucose oxidation may benefit many patients with common brain diseases.

Identification of a common mutation (Gly194Cys) in both Arab Moslem and Ashkenazi Jewish patients with dihydrolipoamide dehydrogenase (E3) deficiency: possible beneficial effect of vitamin therapy

Dihydrolipoamide dehydrogenase (E3) deficiency with a clinical phenotype and genotype (Gly194Cys homozygous) previously identified only in Ashkenazi Jewish patients, was diagnosed in two Palestinian Arab siblings and two unrelated Ashkenazi Jewish patients. While three of the four patients died in childhood without specific treatment, the surviving patient at age 18 years may have benefited from long-term daily supplementation with a cocktail of riboflavin, biotin, coenzyme Q and carnitine.

New disc-based technologies for diagnostic and research applications

The role of genotypic analysis in disease diagnostics and drug response assessment is continually expanding. New genomic discoveries combined with new, novel technologies may provide a greater range of testing capabilities in the near future. We describe the application of nanotechnology, in which DNA microarrays have been placed in a microchannel environment that can be read and analyzed in an optical (CD/DVD) disc drive system. The potential exists to combine molecular and immunological applications together into a rapid, low-cost, high-capacity screening platform. The relevance of this technology is discussed in respect to infectious agent detection, pharmacogenomics, neurogenomics and genetic variations associated with neurologic diseases.

Heterozygous GLDC and GCSH gene mutations in transient neonatal hyperglycinemia

Transient neonatal hyperglycinemia is clinically or biochemically indistinguishable from nonketotic hyperglycinemia at onset. In the case of transient neonatal hyperglycinemia, the elevated plasma and cerebrospinal fluid glycine levels are normalized within 2 to 8 weeks. To elucidate the pathogenesis of transient neonatal hyperglycinemia, we studied three patients by screening mutations in the genes that encode three components of the glycine cleavage system. Heterozygous mutations were identified in all of the three patients, suggesting that transient neonatal hyperglycinemia develops in some heterozygous carriers for nonketotic hyperglycinemia.

Detection of pyruvate dehydrogenase E1 alpha-subunit deficiencies in females by immunohistochemical demonstration of mosaicism in cultured fibroblasts

Deficiency of the E1 alpha-subunit of the pyruvate dehydrogenase (PDH) complex is an X-linked inborn error of metabolism and one of the major causes of lactic acidosis in children. Although most heterozygous females manifest symptoms of the disease, it is often difficult to establish the diagnosis as results based on measurement of total PDH activity, and E1 alpha-immunoreactive protein in patient fibroblasts may be ambiguous because of the variability in the pattern of X chromosome inactivation. We report the development of a set of monoclonal antibodies (MAbs) specific to four subunits of the PDH complex that can be used for detection of PDH E1 alpha deficiency. We also show that anti-E1 alpha and anti-E2 MAbs, when used in immunocytochemical analysis, can detect mosaicism in cell cultures from female patients in which as few as 2-5% of cells express the deficiency. This immunocytochemical approach, which is fast, reliable, and quantitative, will be particularly useful in identifying females with PDH E1 alpha-subunit deficiency as a precursor to mutation analysis.

ATP synthesis in lipoamide dehydrogenase deficiency

Lipoamide dehydrogenase deficiency is an inborn error of several metabolic pathways, including pyruvate metabolism, Krebs cycle, and branched-chain amino acid degradation. The clinical course is variable, ranging from infantile neurodegenerative disease to recurrent episodes of liver failure or myoglobinuria starting later in life. In contrast, residual enzymatic activity in muscle tissue spans over a narrow range. Despite the recent elucidation of the underlying molecular pathology in most patients, relationships between the genotype and the biochemical and clinical phenotype remain unclear. In order to find a suitable assay for the prediction of clinical outcome and assessment of treatment, we have evaluated enzymatic activities and energetic states in fibroblasts from lipoamide dehydrogenase-deficient patients representing three different phenotypes and genotypes. Direct relationships between clinical parameters such as age of onset and disease severity and biochemical characteristics, including lipoamide dehydrogenase activity, pyruvate dehydrogenase complex activity, and ATP production ratio in fibroblasts, were identified. Clinical parameters were not reflected by lactate/pyruvate ratio. ATP production rate was in direct relationship with the severity of the neurological involvement; the patient with reduced ATP synthesis to 30% of the control mean had a severe neurodegenerative disease, whereas ATP synthesis values above 45% were associated with a more favorable course. Incubation of the patients' fibroblasts with dichloroacetate coupled with thiamin resulted in slight but significant improvement of the cell energetic state.

The alpha-ketoglutarate dehydrogenase complex

The alpha-ketoglutarate dehydrogenase complex (KGDHC) is an important mitochondrial constituent, and deficiency of KGDHC is associated with a number of neurological disorders. KGDHC is composed of three proteins, each encoded on a different and well-characterized gene. The sequences of the human proteins are known. The organization of the proteins into a large, ordered multienzyme complex (a "metabolon") has been well studied in prokaryotic and eukaryotic species. KGDHC catalyzes a critical step in the Krebs tricarboxylic acid cycle, which is also a step in the metabolism of the potentially excitotoxic neurotransmitter glutamate. A number of metabolites modify the activity of KGDHC, including inactivation by 4-hydroxynonenal and other reactive oxygen species (ROS). In human brain, the activity of KGDHC is lower than that of any other enzyme of energy metabolism, including phosphofructokinase, aconitase, and the electron transport complexes. Deficiencies of KGDHC are likely to impair brain energy metabolism and therefore brain function, and lead to manifestations of brain disease. In general, the clinical manifestations of KGDHC deficiency relate to the severity of the deficiency. Several such disorders have been recognized: infantile lactic acidosis, psychomotor retardation in childhood, intermittent neuropsychiatric disease with ataxia and other motor manifestations, Friedreich's and other spinocerebellar ataxias, Parkinson's disease, and Alzheimer's disease (AD). A KGDHC gene has been associated with the first two and last two of these disorders. KGDHC is not uniformly distributed in human brain, and the neurons that appear selectively vulnerable in human temporal cortex in AD are enriched in KGDHC. We hypothesize that variations in KGDHC that are not deleterious during reproductive life become deleterious with aging, perhaps by predisposing this mitochondrial metabolon to oxidative damage.

Lipoamide dehydrogenase deficiency due to a novel mutation in the interface domain

An infant with a neurodegenerative disorder accompanied by lactic acidemia is described. In muscle homogenate, the activity of lipoamide dehydrogenase (LAD), the third catalytic subunit of pyruvate dehydrogenase complex (PDHc), alpha-ketoglutarate dehydrogenase complex (KGDHc), and branched-chain keto acid dehydrogenase complex was reduced to 15% of the control. The activity of PDHc was undetectable and the activity of KGDHc was 2% of the control mean. The immunoreactive LAD protein was reduced to about 10% of the control. Direct sequencing of LAD cDNA revealed only one mutation, substituting Asp for Val at position 479 of the precursor form. The mutation resides within the interface domain and likely perturbs stable dimerization. The phenotypic heterogeneity in LAD deficiency is not directly correlated with the residual LAD activity but rather with its impact on the multienzymatic complex activity.

Regulation of mammalian pyruvate dehydrogenase alpha subunit gene expression by glucose in HepG2 cells

We report the effect of glucose on the expression of the gene encoding the pyruvate dehydrogenase (E1) alpha subunit (E1alpha) in human hepatoma (HepG2) cells. Total pyruvate dehydrogenase complex activity as well as the levels of protein and mRNA of the E1alpha subunit were significantly increased in HepG2 cells cultured in medium containing 16.7 mM glucose compared with 1.0 mM glucose for a period of 4 weeks. The level of E1alpha mRNA was elevated approx. 2-fold in HepG2 cells cultured for 24 h in medium containing 16.7 mM glucose compared with 1 mM glucose. This effect was specific to glucose and independent of insulin. Nuclear run-on assays and promoter analysis indicate that the glucose-induced increases in the levels of E1alpha mRNA in HepG2 cells are due to increased transcription of the human E1alpha (PDHA1) gene. Mutational analysis of the E1alpha promoter region has identified two regions, from -78 to -73 bp (CCCCTG) and from -8 to -3 bp (GCGGTG), that are responsible for the effect of glucose on promoter activity; the former exhibits a larger effect. These two sequences represent new variations of the carbohydrate-response element that has been identified in other genes. The stimulation of E1alpha promoter activity by glucose was abolished by okadaic acid at 100 nM but not at 5 nM, suggesting that glucose-mediated regulation of pyruvate dehydrogenase complex E1alpha gene transcription involves a phosphorylation/dephosphorylation mechanism, possibly involving protein phosphatase-1.

Deficiency of dihydrolipoamide dehydrogenase due to two mutant alleles (E340K and G101del). Analysis of a family and prenatal testing

A male child with metabolic acidosis was diagnosed as having dihydrolipoamide dehydrogenase (E3) deficiency. E3 activity of the proband's cultured fibroblasts and blood lymphocytes was 3-9% of normal, while in the parent's lymphocytes it was about 60% of normal. The proband's pyruvate dehydrogenase complex (PDC) and the alpha-ketoglutarate dehydrogenase complex activities from cultured skin fibroblasts were 12% and 6% of normal, respectively. PDC activity in the parents cultured fibroblasts was 25-31% of normal. Western and Northern blot analyses showed similar quantities of E3 protein and mRNA in cultured fibroblasts from the proband and his parents. DNA sequencing of cloned full-length E3 cDNAs, from the proband and the parents, showed two mutations on different alleles of proband were inherited from the parents. One mutation is a three nucleotide (AGG) deletion, from the mother, resulting in deletion of Gly101 in the FAD binding domain. The other mutation is a nucleotide substitution (G to A), from the father, leading to substitution of Lys for Glu340 in the central domain. The same deletion mutation was found in E3 cDNA from a chorionic villus sample and cultured fibroblasts obtained from the mother's subsequent offspring. This finding illustrates the possibility of successful prenatal diagnosis of E3 deficiency utilizing mutations characterized prior to initiation of pregnancy.