Expanding the genetic and phenotypic spectrum of branched-chain amino acid transferase 2 deficiency

The first step in branched-chain amino acid (BCAA) catabolism is catalyzed by the two BCAA transferase isoenzymes, cytoplasmic branched-chain amino acid transferase (BCAT) 1, and mitochondrial BCAT2. Defects in the second step of BCAA catabolism cause maple syrup urine disease (MSUD), a condition which has been far more extensively investigated. Here, we studied the consequences of BCAT2 deficiency, an ultra-rare condition in humans. We present genetic, clinical, and functional data in five individuals from four different families with homozygous or compound heterozygous BCAT2 mutations which were all detected following abnormal biochemical profile results or familial mutation segregation studies. We demonstrate that BCAT2 deficiency has a recognizable biochemical profile with raised plasma BCAAs and, in contrast with MSUD, low-normal branched-chain keto acids (BCKAs) with undetectable l-allo-isoleucine. Interestingly, unlike in MSUD, none of the individuals with BCAT2 deficiency developed acute encephalopathy even with exceptionally high BCAA levels. We observed wide-ranging clinical phenotypes in individuals with BCAT2 deficiency. While one adult was apparently asymptomatic, three individuals had presented with developmental delay and autistic features. We show that the biochemical characteristics of BCAT2 deficiency may be amenable to protein-restricted diet and that early treatment may improve outcome in affected individuals. BCAT2 deficiency is an inborn error of BCAA catabolism. At present, it is unclear whether developmental delay and autism are parts of the variable phenotypic spectrum of this condition or coincidental. Further studies will be required to explore this.

Generation and characterization of two human iPSC lines from patients with methylmalonic acidemia cblB type

Two human induced pluripotent stem cell (iPSC) lines were generated from fibroblasts of two siblings with methylmalonic acidemia cblB type carrying mutations in the MMAB gene: c.287T➔C (p.Ile96Thr) and a splicing loss-of-function variant c.584G➔A affecting the last nucleotide of exon 7 in MMAB (p.Ser174Cysfs*23). Reprogramming factors OCT3/4, SOX2, KLF4 and c-MYC were delivered using a non-integrative method based on the Sendai virus. Once established, iPSCs have shown full pluripotency, differentiation capacity and genetic stability.

Four Years' Experience in the Diagnosis of Very Long-Chain Acyl-CoA Dehydrogenase Deficiency in Infants Detected in Three Spanish Newborn Screening Centers

Identification of very long-chain acyl-CoA dehydrogenase deficiency is possible in the expanded newborn screening (NBS) due to the increase in tetradecenoylcarnitine (C14:1) and in the C14:1/C2, C14:1/C16, C14:1/C12:1 ratios detected in dried blood spots. Nevertheless, different confirmatory tests must be performed to confirm the final diagnosis. We have revised the NBS results and the results of the confirmatory tests (plasma acylcarnitine profiles, molecular findings, and lymphocytes VLCAD activity) for 36 cases detected in three Spanish NBS centers during 4 years, correlating these with the clinical outcome and treatment. Our aim was to distinguish unambiguously true cases from disease carriers in order to obtain useful diagnostic information for clinicians that can be applied in the follow-up of neonates identified by NBS.Increases in C14:1 and of the different ratios, the presence of two pathogenic mutations, and deficient enzyme activity in lymphocytes (<12% of the intra-assay control) identified 12 true-positive cases. These cases were given nutritional therapy and all of them are asymptomatic, except one. Seventeen individuals were considered disease carriers based on the mild increase in plasma C14:1, in conjunction with the presence of only one mutation and/or intermediate residual activity (18-57%). In addition, seven cases were classified as false positives, with normal biochemical parameters and no mutations in the exonic region of ACADVL. All these carriers and the false positive cases remained asymptomatic. The combined evaluation of the acylcarnitine profiles, genetic results, and residual enzyme activities have proven useful to definitively classify individuals with suspected VLCAD deficiency into true-positive cases and carriers, and to decide which cases need treatment.

Pilot Experience with an External Quality Assurance Scheme for Acylcarnitines in Plasma/Serum

The analysis of acylcarnitines (AC) in plasma/serum is established as a useful test for the biochemical diagnosis and the monitoring of treatment of organic acidurias and fatty acid oxidation defects. External quality assurance (EQA) for qualitative and quantitative AC is offered by ERNDIM and CDC in dried blood spots but not in plasma/serum samples. A pilot interlaboratory comparison between 14 European laboratories was performed over 3 years using serum/plasma samples from patients with an established diagnosis of an organic aciduria or fatty acid oxidation defect. Twenty-three different samples with a short clinical description were circulated. Participants were asked to specify the method used to analyze diagnostic AC, to give quantitative data for diagnostic AC with the corresponding reference values, possible diagnosis, and advice for further investigations.Although the reference and pathological concentrations of AC varied among laboratories, elevated marker AC for propionic acidemia, isovaleric acidemia, medium-chain acyl-CoA dehydrogenase, very long-chain acyl-CoA dehydrogenase, and multiple acyl-CoA dehydrogenase deficiencies were correctly identified by all participants allowing the diagnosis of these diseases. Conversely, the increased concentrations of dicarboxylic AC were not always identified, and therefore the correct diagnosis was not reach by some participants, as exemplified in cases of malonic aciduria and 3-hydroxy-3-methylglutaryl-CoA lyase deficiency. Misinterpretation occurred in those laboratories that used multiple-reaction monitoring acquisition mode, did not derivatize, or did not separate isomers. However, some of these laboratories suggested further analyses to clarify the diagnosis.This pilot experience highlights the importance of an EQA scheme for AC in plasma.

Mitochondrial response to the BCKDK-deficiency: Some clues to understand the positive dietary response in this form of autism

Mutations on the mitochondrial-expressed Branched Chain α-Keto acid Dehydrogenase Kinase (BCKDK) gene have been recently associated with a novel dietary-treatable form of autism. But, being a mitochondrial metabolism disease, little is known about the impact on mitochondrial performance. Here, we analyze the mitochondrial response to the BCKDK-deficiency in patient's primary fibroblasts by measuring bioenergetics, ultra-structural and dynamic parameters. A two-fold increase in superoxide anion production, together with a reduction in ATP-linked respiration and intracellular ATP levels (down to 60%) detected in mutants fibroblasts point to a general bioenergetics depletion that could affect the mitochondrial dynamics and cell fate. Ultrastructure analysis of BCKDK-deficient fibroblasts shows an increased number of elongated mitochondria, apparently associated with changes in the mediator of inner mitochondria membrane fusion, GTPase OPA1 forms, and in the outer mitochondrial membrane, mitofusin 2/MFN2. Our data support a possible hyperfusion response of BCKDK-deficient mitochondria to stress. Cellular fate also seems to be affected as these fibroblasts show an altered proportion of the cells on G0/G1 and G2/M phases. Knockdown of BCKDK gene in control fibroblasts recapitulates most of these features. Same BCKDK-knockdown in a MSUD patient fibroblasts unmasks the direct involvement of the accelerated BCAAs catabolism in the mitochondrial dysfunction. All these data give us a clue to understand the positive dietary response to an overload of branched-chain amino acids. We hypothesize that a combination of the current therapeutic option with a protocol that considers the oxidative damage and energy expenditure, addressing the patients' individuality, might be useful for the physicians.

Thirteen years experience with selective screening for disorders in purine and pyrimidine metabolism

Purine and pyrimidine disorders represent a heterogeneous group with variable clinical symptoms and low prevalence rate. In the last thirteen years, we have studied urine/plasma specimens from about 1600 patients and we have identified 35 patients: eight patients with adenylosuccinate lyase deficiency, eight patients with hypoxanthine-guanine phosphoribosyltransferase deficiency, one patient with purine nucleoside phosphorylase deficiency, ten patients with xanthine dehydrogenase deficiency, six patients with molybdenum cofactor deficiency and two patients with dihydropyrimidine dehydrogenase deficiency. Despite low incidence of these diseases, our findings highlight the importance of including the purine and pyrimidine analysis in the selective screening for inborn errors of metabolism in specialized laboratories, where amino acid and organic acid disorders are simultaneously investigated.

Methylmalonic aciduria cblB type: characterization of two novel mutations and mitochondrial dysfunction studies

Methylmalonic aciduria (MMA) cblB type is caused by mutations in the MMAB gene, which codes for the enzyme adenosine triphosphate (ATP): cobalamin adenosyltransferase (ATR). This study reports differences in the metabolic and disease outcomes of two pairs of siblings with MMA cblB type, respectively harbouring the novel changes p.His183Leu/p.Arg190dup (P1 and P2) and the previously described mutations p.Ile96Thr/p.Ser174fs (P3 and P4). Expression analysis showed p.His183Leu and p.Arg190dup to be destabilizing mutations. Both were associated with reduced ATR stability and a shorter half-life than wild-type ATR. Analysis of several parameters related to oxidative stress and mitochondrial function showed an increase in reactive oxygen species (ROS) content, a decrease in mitochondrial respiration and changes in mitochondria morphology and structure in patient-derived fibroblasts compared to control cells. The impairment in energy production and the presence of oxidative stress and fission of the mitochondrial reticulum suggested mitochondrial dysfunction in cblB patients' fibroblasts. The recovery of mitochondrial function should be a goal in efforts to improve the clinical outcome of MMA cblB type.

Severe Neonatal Metabolic Decompensation in Methylmalonic Acidemia Caused by CblD Defect

CblD disorder is an autosomal recessive, rare, heterogeneous disease with variable clinical presentations, depending on the nature and location of the MMADHC gene mutations. Mutations in MMADHC lead to three distinct phenotypes: cblD-MMA, cblD-HC, and cblD-MMA/HC. To date, 18 cblD patients have been reported. Six of them were affected by cblD-MMA, but only three had a known clinical history. One of these patients presented with a metabolic decompensation at 11 months; the second one, born prematurely, was diagnosed with cblD after being treated for intracranial hemorrhage, respiratory distress syndrome, necrotizing enterocolitis, and convulsions at birth; the third one was diagnosed at 5 years of age.Here we present a case of a cblD-MMA patient who had an acute neonatal onset with severe hyperammonemia requiring hemodiafiltration. To the best of our knowledge, this is the first cblD-MMA patient who presented acutely in the newborn period. He has developed well upon treatment with B12, carnitine, and hypoproteic diet. At present time, at the age of 7, he shows normal growth and cognitive development. Thus, it is likely that the aggressive treatment of this child with hemodiafiltration might have prevented him from long-term neurological sequelae. Overall, this case shows that even severe, neonatal-onset patients may display a vitamin B12-responsive MMA. Furthermore, it suggests that an early treatment with vitamins might be beneficial for patients presenting with neonatal-onset hyperammonemia regardless of the suspected disease and before receiving the biochemical diagnosis.

Mitochondrial bioenergetics and dynamics interplay in complex I-deficient fibroblasts

BACKGROUND

Complex I (CI) deficiency is the most frequent cause of OXPHOS disorders. Recent studies have shown increases in reactive oxygen species (ROS) production and mitochondrial network disturbances in patients' fibroblasts harbouring mutations in CI subunits.

OBJECTIVES

The present work evaluates the impact of mutations in the NDUFA1 and NDUFV1 genes of CI on mitochondrial bioenergetics and dynamics, in fibroblasts from patients suffering isolated CI deficiency.

RESULTS

Decreased oxygen consumption rate and slow growth rate were found in patients with severe CI deficiency. Mitochondrial diameter was slightly increased in patients' cells cultured in galactose or treated with 2'-deoxyglucose without evidence of mitochondrial fragmentation. Expression levels of the main proteins involved in mitochondrial dynamics, OPA1, MFN2, and DRP1, were slightly augmented in all patients' cells lines. The study of mitochondrial dynamics showed delayed recovery of the mitochondrial network after treatment with the uncoupler carbonyl cyanide m-chlorophenyl hydrazone (cccp) in patients with severe CI deficiency. Intracellular ROS levels were not increased neither in glucose nor galactose medium in patients' fibroblasts.

CONCLUSION

Our main finding was that severe CI deficiency in patients harbouring mutations in the NDUFA1 and NDUFV1 genes is linked to a delayed mitochondrial network recovery after cccp treatment. However, the CI deficiency is neither associated with massive mitochondrial fragmentation nor with increased ROS levels. The different genetic backgrounds of patients with OXPHOS disorders would explain, at least partially, differences in the pathophysiological manifestations of CI deficiency.

Pseudoexon exclusion by antisense therapy in methylmalonic aciduria (MMAuria)

Development of pseudoexon exclusion therapies by antisense modification of pre-mRNA splicing represents a type of personalized genetic medicine. Here we present the cellular antisense therapy and the cell-based splicing assays to investigate the effect of two novel deep intronic changes c.1957-898A>G and c.1957-920C>A identified in the methylmalonyl-coenzyme A (CoA) mutase (MUT) gene. The results show that the nucleotide change c.1957-898A>G is a pathological mutation activating pseudoexon insertion and that antisense morpholino oligonucleotide (AMO) treatment in patient fibroblasts leads to recovery of MUT activity to levels 25 to 100% of control range. On the contrary, the change c.1957-920C>A, identified in two fibroblasts cell lines in cis with c.1885A>G (p.R629G) or c.458T>A (p.D153V), appears to be a rare variant of uncertain clinical significance. The functional analysis of c.1885A>G and c.458T>A indicate that they are the disease-causing mutations in these two patients. The results presented here highlight the necessity of scanning the described intronic region for mutations in MUT-affected patients, followed by functional analyses to demonstrate the pathogenicity of the identified changes, and extend previous work of the applicability of the antisense approach in methylmalonic aciduria (MMAuria) for a novel intronic mutation.

Creatine transporter deficiency in two adult patients with static encephalopathy

Creatine transporter deficiency is a recently identified X-linked inborn error of metabolism. The natural course of the disease is not well delineated since clinical data from adult patients have scarcely been reported. A progressive course of the disease has been noted in a few described cases. We report the first two Spanish adult patients with creatine transporter deficiency and compare their clinical phenotype and the evolution of the disease with those of other published cases. The two brothers were identified in a study of a cohort of 610 mentally handicapped male patients. The disease was detected by biochemical studies and confirmed by DNA studies. The most significant clinical features were mental retardation, epilepsy and autistic behaviour, and these symptoms did not worsen, in contrast to other reports. They did not present gastrointestinal problems or movement disorders. Creatine transporter deficiency could be an underdiagnosed metabolic disorder and should be considered in adult patients with mental retardation. Clinical presentation of this disorder showed marked differences among adult patients and the course of the disease was static in our cases. Detection of additional adult patients might allow better understanding of the phenotypic outcome at a later age.

Urinary guanidinoacetate and creatine levels in patients with HPRT deficiency

Neurobehavioral manifestations of complete HPRT deficiency include severe action dystonia, choreathetosis, alteration of executive functions, and self-injurious behavior. Dystonic manifestations are also present in patients with partial HPRT deficiency. Pathophysiology of these manifestations is unknown. Guanidinoacetate is a neurotoxin implicated in certain dystonic syndromes. We have examined guanidinoacetate and creatine levels in urine from 11 HPRT deficient patients (9 with Lesch-Nyhan syndrome and 2 with partial deficiency). Urinary guanidinoacetate and creatine levels in HPRT deficient patients were within the normal range. Guanidinoactetate alteration does not seem to be implicated in the pathogenesis of the neurological disease associated with HPRT deficiency.

Methylmalonic acidaemia: examination of genotype and biochemical data in 32 patients belonging to mut, cblA or cblB complementation group

Methylmalonic acidaemia (MMA) is a genetic disorder caused by defects in methylmalonyl-CoA mutase or in any of the different proteins involved in the synthesis of adenosylcobalamin. The aim of this work was to examine the biochemical and clinical phenotype of 32 MMA patients according to their genotype, and to study the mutant mRNA stability by real-time PCR analysis. Using cellular and biochemical methods, we classified our patient cohort as having the MMA forms mut (n = 19), cblA (n = 9) and cblB (n = 4). All the mut (0) and some of the cblB patients had the most severe clinical and biochemical manifestations, displaying non-inducible propionate incorporation in the presence of hydroxocobalamin (OHCbl) in vitro and high plasma odd-numbered long-chain fatty acid (OLCFA) concentrations under dietary therapy. In contrast, mut (-) and cblA patients exhibited a milder phenotype with propionate incorporation enhanced by OHCbl and normal OLCFA levels under dietary therapy. No missense mutations identified in the MUT gene, including mut (0) and mut (-) changes, affected mRNA stability. A new sequence variation (c.562G>C) in the MMAA gene was identified. Most of the cblA patients carried premature termination codons (PTC) in both alleles. Interestingly, the transcripts containing the PTC mutations were insensitive to nonsense-mediated decay (NMD).

Persistent increase of plasma butyryl/isobutyrylcarnitine concentrations as marker of SCAD defect and ethylmalonic encephalopathy

High concentrations of butyryl/isobutyrylcarnitine (C(4)-carnitine) in plasma with increase of ethylmalonic acid (EMA) in urine point to different genetic entities, and further investigations are required to differentiate the possible underlying defect. Here we report three unrelated cases, two neurologically affected and one asymptomatic, with this abnormal metabolite pattern due either to mutations in the ETHE1 gene or to a short-chain acyl-CoA dehydrogenase (SCAD) defect.

[Glutaric aciduria type 1 with normal evolution: follow-up of one case until adult age]

We present a patient of 20 years of age with glutaric aciduria type 1 (GA1) and normal psychomotor development. Her symptoms consisted of a few convulsions between 2.5 and 4.5 years of age. She was diagnosed at 9 years of age because of the typical alterations of GA1 that appeared in computed tomography and magnetic resonance (MR) imaging studies. Enzymatic activity in fibroblasts culture was nonexistent and glutarate excretion was elevated in the annual controls where this was investigated from the diagnosis of the disease so far. MR studies showed hyposignal in T1 of the subcortical white matter, severe dilatation of the Sylvian region and temporal fossa subarachnoid spaces, and hypoplasia of the subjacent cerebral parenchyma and of both temporal lobes. The corpus callosum and the surrounding zones appeared very enlarged and with signal changes. Spectroscopic MR showed signs of membrane instability and cellular impoverishment in subcortical white matter and basal ganglia and presence of lactic acid. Macrocephaly always maintained centiles over 98. The patient has no abnormal movements or motor disturbances, her behavior and intelligence being normal and she is able to follow studies of middle level.

Prenatal diagnosis of propionic acidemia

In this report we summarize our experience in prenatal diagnosis of propionic acidemia (PA) since 1987. Overall, we have investigated 25 pregnancies at risk from 19 unrelated families. Until genetic structure of the genes involved in PA was elucidated, prenatal diagnosis has been successfully performed by means of metabolite quantitation and/or enzymatic assays in foetal issue. Today, direct propionyl-CoA carboxylase activity assay in combination with molecular analysis in chorion villi can be regarded as a fast and reliable method of choice for prenatal diagnosis of this organic acidemia.

Correlation of genotype and phenotype in glutaryl-CoA dehydrogenase deficiency

We have investigated the correlation between genotype and phenotype in a large number of patients with glutaric aciduria type I (GA I). The deficiency of glutaryl-CoA dehydrogenase has been confirmed in the Rigshospitalet's laboratory in 215 patients since 1975. Most of the patients were of European ancestry. Complete absence of enzyme activity was found in more than half of the patients, while 34% of patients had a residual activity up to 5% and a few patients had a residual activity of 5-15%. In four exceptional cases, a very high residual activity of up to 30% was found. Enzyme studies are thus a reliable method for confirming the diagnosis of GA I, although it may be difficult to distinguish exceptional 'mild' cases from heterozygous carriers for GA I. Three of the patients with very high residual activity are compound heterozygous for the missense mutations R227P and V400M, both of which are associated with residual enzyme activity of 8-10% in homozygous patients. Patients with a mild mutation on at least one chromosome frequently show unusual biochemical findings such as low or normal urinary excretion of glutaric acid and mild or only slightly increased excretion of 3-hydroxyglutaric acid. In contrast, patients with severe mutations such as R402W or A293T on both alleles have no residual activity and show the typical urinary metabolite pattern. Clinical data were available for a subgroup of 79 patients. No correlation with the biochemical phenotype or the genotype could be established.

Screening for adenylosuccinate lyase deficiency: clinical, biochemical and molecular findings in four patients

Adenylosuccinate lyase deficiency is an autosomal recessive defect of purine metabolism. Succinyladenosine (S-Ado) and succinylaminoimidazole carboxamide riboside (SAICAr) are the disease marker metabolites in physiological fluids. The Bratton-Marshall test for detection of SAICAr in urine has been added to the selective screening for inborn errors of metabolism that is carried out in our lab. During the last three years, around 2,000 patients have been screened by this method, resulting in the detection of four new cases with this disease. They all presented with severe psychomotor delay, hypotonia and refractory epilepsy since the neonatal period. The S-Ado/SAICAr ratio in cerebrospinal fluid was below 2, indicating that they correspond to the most severe form of the disease. New missense mutations were found in a heterozygous fashion in three patients. The study of purines in all patients with neurological disease of unknown etiology is highly recommended.

[Bilateral hypodensity of the basal ganglia. Clinico-evolutionary correlation in children]

INTRODUCTION

The presence in neuroimaging of areas of symmetrical bilateral hypodensity in the basal ganglia (SBHBG) is a striking and unusual finding.

OBJECTIVE

To determine the aetiology, clinical significance and evolution of a group of paediatric patients with SBHBG.

PATIENTS AND METHODS

We made a study of 21 patients with neuroimaging studies (CT or MR) showing SBHBG. The affected area was related to the aetiology, clinical features and evolution.

RESULTS

The ages varied between 4 months and 16 years. In 7 cases Leigh s disease was diagnosed, 5 had had acute hypoxia, 4 type I glutaric aciduria, and 1 case each of methylmalonic aciduria, Ia gluconeogenesis, CO intoxication, acute striatal necrosis and bacterial meningitis. The putamen was affected in 6 cases, globus pallidus in 4 cases and the lenticular nucleus was damaged in the rest. Three cases also had lesions in the caudate nucleus. MR was better than CT for localization of the precise area involved. Clinically, 13 cases had extrapyramidal signs. We found no relation between the size, localization of the lesion and the prognosis, which was more dependent on the aetiology, only one patient (CO intoxication) recovered and eight died (Leigh s disease and 1 case of hypoxia).

CONCLUSIONS

The presence of SBHBG in a patient makes extensive study necessary to find the aetiology. It is a nonspecific finding, usually of metabolic origin and with little correlation with the clinical condition. Its presence implies a poor prognosis and raises suspicion of the presence of certain neurological disorders.

Prenatal molecular diagnosis of glutaric aciduria type I by direct mutation analysis

Various biochemical strategies are followed for the prenatal diagnosis of glutaric aciduria type I (GA I). However, since the description of patients with normal excretion of glutarate and significant residual activity, the difficulties of prenatal biochemical diagnosis are obvious. The characterization of the glutaryl-CoA dehydrogenase (GCDH) gene has allowed us to develop a single strand conformation polymorphism (SSCP) screening method, followed by direct sequencing, to identify the disease causing mutations in patients with GA I. Here we report the first prenatal diagnoses based on DNA analysis in chorionic villi biopsy or cultured amniotic fluid cells in three families at risk for GA I. Our results show that this strategy provides a fast and reliable method for prenatal diagnosis. In addition we report two new mutations (1209-1210ins G and R161W) in the GCDH gene that occurred at hypermutable loci.

Glutaryl-CoA dehydrogenase deficiency in Spain: evidence of two groups of patients, genetically, and biochemically distinct

Glutaryl-CoA dehydrogenase (GCDH) deficiency causes glutaric aciduria type I (GA I), an inborn error of metabolism that is characterized clinically by dystonia and dyskinesia and pathologically by neural degeneration of the caudate and putamen. Studies of metabolite excretion allowed us to categorize 43 GA I Spanish patients into two groups: group 1 (26 patients), those presenting with high excretion of both glutarate and 3-hydroxyglutarate, and group 2 (17 patients), those who might not be detected by routine urine organic acid analysis because glutarate might be normal and 3-hydroxyglutarate only slightly higher than controls. Single-strand conformation polymorphism (SSCP) screening and sequence analysis of the 11 exons and the corresponding intron boundaries of the GCDH gene allowed us to identify 13 novel and 10 previously described mutations. The most frequent mutations in group 1 were A293T and R402W with an allele frequency of 30% and 28%, respectively. These two mutations were also found in group 2, but always in heterozygosity, in particular in combination with mutations V400M or R227P. Interestingly, mutations V400M and R227P were only found in group 2, and at least one of these mutations was found in 11 of 15 unrelated alleles, accounting together for 53% of the mutant alleles in group 2. Therefore, it seems clear that two genetically and biochemically distinct groups of patients exist. The severity of the clinical phenotype seems to be closely linked to the development of encephalopathic crises rather than to residual enzyme activity or genotype. Comparison of GCDH protein with other acyl-CoA dehydrogenases (whose x-ray crystal structure has been determined) reveals that most of the mutations identified in GCDH protein seem to affect folding and tetramerization, as has been described for a number of mutations affecting mitochondrial beta-oxidation acyl-CoA dehydrogenases.

Potential relationship between genotype and clinical outcome in propionic acidaemia patients

Propionic acidaemia (PA) is an autosomal recessive disorder caused by mutations in either of the PCCA or PCCB genes which encode the alpha and beta subunits, respectively, of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). In this work we have examined the biochemical findings and clinical outcome of 37 Spanish PA patients in relation to the mutations found in both PCCA and PCCB genes. We have detected 27 early-onset and 101 late-onset cases, showing remarkably similar biochemical features without relation to either the age of onset of the disease or the defective gene they have. Twenty-one of the patients have so far survived and three of them, now adolescents, present normal development. Different biochemical procedures allowed us to identify the defective gene in 9 PCCA deficient and 28 PCCB deficient patients. Nine putative disease-causing mutations accounting for 77.7% of mutant alleles were identified among PCCA deficient patients, each one carrying a unique genotypic combination. Of PCCB mutant alleles 98% were characterised. Four common mutations (ins/del, E168K, 1170insT and A497V) were found in 38/52 mutant chromosomes investigated, whereas the remainder of the alleles harbour 12 other different mutations. By examining the mutations identified both in PCCA and PCCB genes and the clinical evolution of patients, we have found a good correlation between certain mutations which can be considered as null with a severe phenotype, while certain missense mutations tend to be related to the late and mild forms of the disease. Expression studies, particularly of the missense mutations identified are necessary but other genetic and environmental factors probably contribute to the phenotypic variability observed in PA.

Adolescent myopathic presentation in two sisters with very long-chain acyl-CoA dehydrogenase deficiency

Two sisters were investigated at the ages of 20 and 13 years owing to persistently increased serum creatine kinase and recurrent episodes of rhabdomyolysis after emotional stress in the older and myalgias in the younger. The finding of increased levels of cis-5-tetradecenoic acid (C14:1) in plasma, severe hypocarnitinaemia and the absence of a pathological dicarboxylic aciduria in both sisters suggested a very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. Reduced [1-(14)C]palmitate oxidation and deficient mitochondrial VLCAD activity in fibroblasts were found. Mutation analysis revealed compound heterozygosity for Asp365His and Arg410His changes. This late-onset, milder clinical presentation differs from the other two more severe infantile phenotypes described, since there is no hypoglycaemia or cardiac disease. Fatty acid oxidation defects should be investigated in all cases with rhabdomyolysis beginning in adolescence or early adulthood.

Reliability of biochemical parameters used in prenatal diagnosis of combined methylmalonic aciduria and homocystinuria

Prenatal diagnosis for combined methylmalonic aciduria and homocystinuria was performed in five at-risk pregnancies by determination of methylmalonic acid (MMA) and total homocysteine (Hcy) in amniotic fluid supernatant. The incorporation rate of [14C] propionate (+/- OHCbl) and the synthesis of cobalamin derivatives in cultured amniocytes were investigated as well as the [14C] MTHF incorporation rate in intact chorion biopsy. Our experience showed that total Hcy and MMA were clearly elevated in amniotic fluid of affected fetuses. Both the study of [14C] propionate incorporation and that of cobalamin synthesis in cultured amniocytes are useful to confirm the results of metabolite determination. The incorporation of [14C] MTHF in intact chorion biopsy seems not to be a reliable diagnostic method.

An unusual late-onset case of propionic acidaemia: biochemical investigations, neuroradiological findings and mutation analysis

We report a 5-year-old boy with propionic acidaemia who developed a rapidly fatal necrosis of the basal ganglia after an episode of clinical deterioration. Neither metabolic acidosis nor hyperammonaemia were present. Organic acid analysis in both urine and CSF showed increased levels of methylcitric and 3-hydroxypropionic acids. Propionic acidaemia was confirmed by demonstrating a propionyl-CoA carboxylase deficiency (11% of control value) in skin fibroblasts. DNA analysis revealed that the patient was a compound heterozygote for two mutations in the PCCB gene.

CONCLUSION

Propionic acidaemia can present as a sudden and fatal neurological disease and not only as an organic aciduria with severe biochemical dis-turbances and progressive neurological deterioration.

A nonsense mutation in the exon 2 of the 3-hydroxy-3-methylglutaryl coenzyme A lyase (HL) gene producing three mature mRNAs is the main cause of 3-hydroxy-3-methylglutaric aciduria in European Mediterranean patients

3-Hydroxy-3-methylglutaric aciduria is a rare recessive monogenic disorder that affects ketogenesis and the catabolism of L-leucine. We report the biochemical and molecular characterization of a mutation in the 3-hydroxy-3-methylglutaryl coenzyme A lyase gene in four new probands, three Spanish and one Turkish, affected by 3-hydroxy-3-methylglutaric aciduria, all homozygous for the nonsense mutation Glu37Ter, which was reported by our group in two probands of Portuguese and Moroccan origin (15). In addition to the aberrant mRNAs found in the two previous probands, a novel species of mature HL mRNA was observed in the patients studied here, since a new cDNA, skipped in exons 2 and 3, was obtained from the mRNAs by reverse-transcription PCR (RT-PCR). Thus, three mRNA species were produced in aberrant splicings as a result of this nonsense mutation: (i) one of the expected size that contains the premature stop codon UAA, (ii) another with a deletion of 84 bp corresponding to the whole of exon 2, and (iii) a new species found now, with a deletion of 192 bp corresponding to skipping of the whole of exons 2 and 3, whose translation product led to the loss of seven amino acids in the leader peptide and 57 amino acids in the terminal domain of the mature enzyme. The association of a nonsense mutation with the skipping of the exon that contains it, plus the following exon, is an unusual finding not seen previously in HL deficiencies. The mutation described here shows the highest incidence (> 37%) of total HL deficiencies reported.

Variable clinical and biochemical presentation of seven Spanish cases with glutaryl-CoA-dehydrogenase deficiency

In this report, we describe seven new patients with a severe deficiency of glutaryl-CoA dehydrogenase in cultured skin fibroblasts. Three of the patients studied excreted high levels of glutaric acid. The remaining four patients presented a lack of significant glutaric aciduria. However, glutaric acid was found in increased levels in CSF. In both groups of patients, the urine glutaric acid levels were not related to their metabolic condition at the time of sampling. Hypocarnitinemia was a common finding. Some patients also showed defects on respiratory chain complexes in muscle biopsy. Only one patient has a normal psychomotor development. The other six patients are severely handicapped despite the attempts of different therapies. In patients with progressive neurological deterioration with dystonia and cerebellar signs associated with temporal lobe atrophy and bilateral basal ganglia damage on MRI, a glutaric aciduria type I (GA I) should always be investigated. The presence of glutaric acid in body fluids, especially in CSF, as well as plasma carnitine levels, should be determined. These procedures can lead to the diagnosis of glutaric aciduria type I.

[Complex I and IV deficits in the mitochondrial respiratory chain in two siblings with type I glutaric aciduria]

We report two brothers with a glutaric aciduria type I (GA-I) identified by Glutaryl-coenzyme A dehydrogenase deficiency in skin fibroblasts. The onset of neurologic abnormalities was at 6 and 9 months of age as an acute Reye-like presentation in one. Because of the hyperlactacidemia, hyperlactatorrachia, mitochondrial abnormalities in muscular cells and a deficiency in complex I and IV of the respiratory chain in isolated mitochondria from muscle, a presumptive diagnosis of Leigh syndrome was made. We analyze the difference between both disorders. GA-I should be suspected in patients with acute dystonia and psychomotor regression, lactic acidosis and hypodensity of the basal ganglia.

First report of prenatal diagnosis of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency in a pregnancy at risk

Prenatal diagnosis of long-chain 3-hydroxyacyl-CoA dehydrogenase (3-HAD) deficiency was performed in a family at risk. The diagnosis of an affected fetus was carried out by enzyme assay in cultured chorionic villus cells.

Investigation of enzyme defects in children with lactic acidosis

Screening for enzyme deficiencies was carried out in cultured skin fibroblasts and leukocytes of 19 patients with lactic acidosis and neurological problems. Pyruvate carboxylase deficiency was demonstrated in three cases. Reduced pyruvate oxidation was found in seven cultures; six showed no significant stimulation of the oxidation rate by methylene blue and in three a decreased pyruvate dehydrogenase complex activity was confirmed. Methylene blue restored a near normal oxidation rate in the seventh culture which had decreased cytochrome c oxidase activity.

Non-ketotic hyperglycinaemia: glycine/serine ratio in amniotic fluid--an unreliable method for prenatal diagnosis

We describe a prenatal diagnosis of a fetus at risk for non-ketotic hyperglycinaemia based on the glycine/serine ratio in amniotic fluid at 16 weeks of gestation. Although the glycine level and the glycine/serine ratio in amniotic fluid were within the normal range, the fetus was affected and therefore a false-negative prediction was made. The reliability of this method is questioned.

A new patient with dicarboxylic aciduria suggestive of medium-chain Acyl-CoA dehydrogenase deficiency presenting as Reye's syndrome

A new patient with medium-chain dicarboxylic aciduria and suberyl glycinuria during an attack of acute illness is reported. When, inadvertently he was given medium-chain triglycerides for 2 days, the excretion of abnormal metabolites of medium-chain fatty acids increased and hepatomegaly became more pronounced. During remission a low excretion of the metabolites were observed. After 16 h of fasting hypoglycaemia was accompanied by an increase of urinary dicarboxylic acids and psi-hydroxyacids similar to that found on admission. Interestingly this urinary organic acid pattern persisted 8 h after intravenous administration of glucose. In a blood sample obtained after 16 h of fasting there was hypoketonaemia and increased levels of total free fatty acids, octanoic, decanoic and cis-4-decenoic acids. These biochemical data suggest the existence of a deficiency at the level of medium-chain acyl-CoA dehydrogenase.

[3 patients with maple syrup urine disease]

Clinical manifestations, biochemistry and treatment of three patients with the inherited alteration of the so called maple syrup urine disease are presented. Diagnosis was based upon both detection of high concentrations of leucine, isoleucine, valine and their corresponding alpha-ketoacids in plasma and urine, and existence of a peculiar odor as well as an intense, progressive, neurological alteration. Considering the early onset of clinical symptoms, low protein tolerance and very reduced rate of leucine decarboxylation in cultured fibroblasts, the three patients exhibited grade I, classical type of this disease. None of them responded favorably to suprapharmacological doses of thiamine. Treatment of the patients is discussed and compared with that recommended in the literature.

[Human fibroblast bank for studying amino acid disorders and organic acidemias]

The establishment of a fibroblast bank from patients with biochemical alterations in the metabolism of aminoacids and organic acids has been initiated. The patients suffered from distinct variants of maple syrup urine disease, propionic acidaemia, methylmalonic acidaemia, lactic acidosis and hyperglycinuria. Thirty six human cell lines corresponding to patients with these diseases, their relatives and control individuals have been accumulated.

Dietary treatment and biochemical studies on a neonatal case of propionyl-CoA carboxylase deficiency

The case of a patient with neonatal propionic acidaemia is reported. Despite an initially favourable response to the administration of an artificial formula, the patient finally died when 9.5 months old. Protein tolerance never exceeded 1.3 g kg-1 day-1. During the remission periods, when ingesting the formula, 3-hydroxypropionic acid was excreted alone or together with tiglylglycine and/or methylcitrate. In a period of ketoacidosis, in addition to these three metabolites and those of ketoacidosis, elevations of 2-methyl-3-oxovaleric acid, propionylglycine and 2-methyl-3-hydroxybutyric acid were found. A severe deficiency of propionyl-CoA carboxylase in cultured fibroblasts was detected; biotin, when added to the fibroblasts culture media, did not stimulate this enzyme activity. The effectiveness of the administered formula is discussed.

Late onset type of propionic acidaemia: case report and biochemical studies

A late-onset case of propionic acidaemia with favourable response to restriction of dietary protein is described. During a keto-acidotic crisis, this patient demonstrated unexpectedly low concentrations of propionic acid and glycine in blood and urine but increased urinary output of some secondary metabolites.