Acetoacetyl CoA thiolase deficiency: a cause of severe ketoacidosis in infancy simulating salicylism

The recent insights into the function of ACAT1: A possible anti-cancer therapeutic target

Acetoacetyl-CoA thiolase also known as acetyl-CoA acetyltransferase (ACAT) corresponds to two enzymes, one cytosolic (ACAT2) and one mitochondrial (ACAT1), which is thought to catalyse reversible formation of acetoacetyl-CoA from two molecules of acetyl-CoA during ketogenesis and ketolysis respectively. In addition to this activity, ACAT1 is also involved in isoleucine degradation pathway. Deficiency of ACAT1 is an inherited metabolic disorder, which results from a defect in mitochondrial acetoacetyl-CoA thiolase activity and is clinically characterized with patients presenting ketoacidosis. In this review I discuss the recent findings, which unexpectedly expand the known functions of ACAT1, indicating a role for ACAT1 well beyond its classical activity. Indeed ACAT1 has recently been shown to possess an acetyltransferase activity capable of specifically acetylating Pyruvate DeHydrogenase (PDH), an enzyme involved in producing acetyl-CoA. ACAT1-dependent acetylation of PDH was shown to negatively regulate this enzyme with a consequence in Warburg effect and tumor growth. Finally, the elevated ACAT1 enzyme activity in diverse human cancer cell lines was recently reported. These important novel findings on ACAT1's function and expression in cancer cell proliferation point to ACAT1 as a potential new anti-cancer target.

Recent advances in understanding beta-ketothiolase (mitochondrial acetoacetyl-CoA thiolase, T2) deficiency

Beta-ketothiolase (mitochondrial acetoacetyl-CoA thiolase, T2) deficiency (OMIM #203750, *607809) is an inborn error of metabolism that affects isoleucine catabolism and ketone body metabolism. This disorder is clinically characterized by intermittent ketoacidotic crises under ketogenic stresses. In addition to a previous 26-case series, four series of T2-deficient patients were recently reported from different regions. In these series, most T2-deficient patients developed their first ketoacidotic crises between the ages of 6 months and 3 years. Most patients experienced less than three metabolic crises. Newborn screening (NBS) for T2 deficiency is performed in some countries but some T2-deficient patients have been missed by NBS. Therefore, T2 deficiency should be considered in patients with severe metabolic acidosis, even in regions where NBS for T2 deficiency is performed. Neurological manifestations, especially extrapyramidal manifestations, can occur as sequelae to severe metabolic acidosis; however, this can also occur in patients without any apparent metabolic crisis or before the onset of metabolic crisis.

Mitochondrial β-oxidation of saturated fatty acids in humans

Mitochondrial β-oxidation of fatty acids generates acetyl-coA, NADH and FADH₂. Acyl-coA synthetases catalyze the binding of fatty acids to coenzyme A to form fatty acyl-coA thioesters, the first step in the intracellular metabolism of fatty acids. l-carnitine system facilitates the transport of fatty acyl-coA esters across the mitochondrial membrane. Carnitine palmitoyltransferase-1 transfers acyl groups from coenzyme A to l-carnitine, forming acyl-carnitine esters at the outer mitochondrial membrane. Carnitine acyl-carnitine translocase exchanges acyl-carnitine esters that enter the mitochondria, by free l-carnitine. Carnitine palmitoyltransferase-2 converts acyl-carnitine esters back to acyl-coA esters at the inner mitochondrial membrane. The β-oxidation pathway of fatty acyl-coA esters includes four reactions. Fatty acyl-coA dehydrogenases catalyze the introduction of a double bond at the C2 position, producing 2-enoyl-coA esters and reducing equivalents that are transferred to the respiratory chain via electron transferring flavoprotein. Enoyl-coA hydratase catalyzes the hydration of the double bond to generate a 3-l-hydroxyacyl-coA derivative. 3-l-hydroxyacyl-coA dehydrogenase catalyzes the formation of a 3-ketoacyl-coA intermediate. Finally, 3-ketoacyl-coA thiolase catalyzes the cleavage of the chain, generating acetyl-coA and a fatty acyl-coA ester two carbons shorter. Mitochondrial trifunctional protein catalyzes the three last steps in the β-oxidation of long-chain and medium-chain fatty acyl-coA esters while individual enzymes catalyze the β-oxidation of short-chain fatty acyl-coA esters. Clinical phenotype of fatty acid oxidation disorders usually includes hypoketotic hypoglycemia triggered by fasting or infections, skeletal muscle weakness, cardiomyopathy, hepatopathy, and neurological manifestations. Accumulation of non-oxidized fatty acids promotes their conjugation with glycine and l-carnitine and alternate ways of oxidation, such as ω-oxidation.

Clinical presentation and outcome in a series of 32 patients with 2-methylacetoacetyl-coenzyme A thiolase (MAT) deficiency

2-methylacetoacetyl-coenzyme A thiolase (MAT) deficiency, also known as beta-ketothiolase deficiency, is an inborn error of ketone body utilization and isoleucine catabolism. It is caused by mutations in the ACAT1 gene and may present with metabolic ketoacidosis. In order to obtain a more comprehensive view on this disease, we have collected clinical and biochemical data as well as information on ACAT1 mutations of 32 patients from 12 metabolic centers in five countries. Patients were between 23months and 27years old, more than half of them were offspring of a consanguineous union. 63% of the study participants presented with a metabolic decompensation while most others were identified via newborn screening or family studies. In symptomatic patients, age at manifestation ranged between 5months and 6.8years. Only 7% developed a major mental disability while the vast majority was cognitively normal. More than one third of the identified mutations in ACAT1 are intronic mutations which are expected to disturb splicing. We identified several novel mutations but, in agreement with previous reports, no clear genotype-phenotype correlation could be found. Our study underlines that the prognosis in MAT deficiency is good and MAT deficient individuals may remain asymptomatic, if diagnosed early and preventive measures are applied.

First report of 3-oxothiolase deficiency in iran

INTRODUCTION

Mitochondrial acetoacetyl-CoA thiolase (3-oxothiolase) deficiency is a rare metabolic disorder involving ketone body metabolism characterized by acute attacks of vomiting, acidosis, ketosis, and lethargy along with some laboratory criteria including excessive excretion of 2-methyl-3-hydroxybutyric acid in urine.

CASE PRESENTATION

This is a case report of 3-oxothiolase deficiency in a young Iranian boy with presentation of intractable vomiting and severe metabolic acidosis following a common cold in six months of age with abundant urinary 2-methyl-3- hydroxybutyric acid.

DISCUSSION

This is the first Iranian 3-oxothiolase deficiency case report as searched in the literature. Because of the high rate of consanguineous marriages in Iran, physicians should consider the 3-oxothiolase deficiency in the differential diagnosis of any patient with intractable vomiting and severe metabolic acidosis.

Different clinical presentation in siblings with mitochondrial acetoacetyl-CoA thiolase deficiency and identification of two novel mutations

Mitochondrial acetoacetyl-CoA thiolase (T2) catalyzes 2-methylacetoacetyl-CoA cleavage into acetyl-CoA and propionyl-CoA in isoleucine catabolism and interconversion between acetyl-CoA and acetoacetyl-CoA in ketone body metabolism. T2 deficiency is a rare metabolic disease of autosomal recessive inheritance. The disorder is characterized by intermittent ketoacidotic episodes. The onset of clinical symptoms is in the infant or toddler period. The frequency of episodes declines with age, stopping before adolescence. Here we report two siblings with this disorder. The proband (GK65) is a French girl born from non-consanguineous parents. She presented several ketoacidotic episodes with 5 hospitalizations from age 2 to 4 years, the first of them complicated by ketoacidotic coma. Minor episodes, which are generally provoked by infections or high protein intake, still persist at age of 16 years. Molecular analysis of the T2 gene has revealed the compound heterozygosity of c.578T>C (M193T) and IVS8+5g>t. The latter mutation results in skipping of exon 8. In contrast, the younger brother (GK65b) had a unique ketoacidotic crisis at the age of 6 years that is the oldest-age first crisis among T2-deficient patients reported thus far. Despite the mild phenotype, he carried the same T2 gene mutations as his sister (GK65). Furthermore, T2 catalytic activity and T2 protein were not detected in the fibroblasts derived from GK65 and GK65b. In conclusion, the siblings with the same T2 gene mutations present different clinical severity. Diagnostic testing for asymptomatic siblings is important in the management of T2-deficient families.

An unusual cause of interference in a salicylate assay caused by mitochondrial acetoacetyl-CoA thiolase deficiency

Mitochondrial acetoacetyl-CoA thiolase deficiency (or beta-ketothiolase deficiency) is a rare metabolic disorder characterized by acute episodes of severe acidosis and ketosis. A case is presented of an 18-month-old boy who presented with vomiting and diarrhoea and was found to be markedly acidotic. When the acidosis persisted despite saline fluid boluses and bicarbonate correction, further investigations were undertaken. Routine biochemical investigation revealed detectable salicylate concentrations despite the parents denying its administration, which initially caused some diagnostic confusion. The results of urine organic acid analysis, however, confirmed that the diagnosis of mitochondrial acetoacetyl-CoA thiolase deficiency. The high concentrations of acetoacetate present in the patient's sample resulted in a false-positive reaction in the Trinder assay for salicylate.

Kinetic and expression analyses of seven novel mutations in mitochondrial acetoacetyl-CoA thiolase (T2): identification of a Km mutant and an analysis of the mutational sites in the structure

Mitochondrial acetoacetyl-CoA thiolase (T2) deficiency is an inborn error of metabolism that affects isoleucine catabolism and ketone body metabolism. We identified 7 novel and 2 previously reported mutations in six T2-deficient patients. Transient expression analysis of wild-type and eight mutant cDNAs was performed at 40, 37 and 30 degrees C. Although no significant residual activity was detected, mutant proteins were detected in the N158D, N158S, R208Q, Y219H and N282H mutants. Accumulation of these mutant proteins was temperature-sensitive with the highest expression levels at lower temperatures. Expression of Q73P and N353K cDNAs yielded neither residual T2 protein nor enzyme activity. An E252del mutant T2 was detected with a relative protein amount and enzyme activity of 30% and 25%, respectively, in comparison to the wild-type at 37 degrees C. The E252del mutant protein was more stable at 30 degrees C expression than 37 degrees C, but was essentially undetectable at 40 degrees C, indicating its temperature-sensitive instability. Kinetic studies revealed a twofold K(m) elevation for substrates coenzyme A and acetoacetyl-CoA in the E252del mutant, while V(max) was comparable to the wild-type. We conclude that the E252del is a temperature-sensitive K(m) mutant. This correlates well with the effect predicted from the T2 tertiary structure analysis, using the crystal structure of the human T2 homotetramer. The probable effect of the other mutations on the T2 tertiary structure was also evaluated.

Inborn errors of isoleucine degradation: a review

Three inborn errors have been identified in the pathway of isoleucine degradation. Deficiency of beta-ketothiolase (beta-KT, also known as T2, mitochondrial acetoacetyl-CoA thiolase and acetyl-CoA acetyltransferase 1) is a well-described disorder which presents with acute episodic ketoacidosis. In contrast, short/branched-chain acyl-CoA dehydrogenase (SBCAD) and 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiencies are recently described and relatively rare defects which present with predominantly neurological manifestations, although acute metabolic decompensation may occur in the early newborn period. Careful examination of urine organic acids is required for identification and differential diagnosis of these disorders, with awareness that the abnormalities may be subtle and variable. Tandem MS analysis of acylcarnitines may reveal elevated C5 (SBCAD) or C5:1 and/or OH-C5 species (MHBD and beta-KT deficiencies) but the abnormalities are non-diagnostic and may be intermittent or absent. Confirmation of diagnosis is therefore advisable by specific enzyme assay and/or mutation analysis of the ACAT1 (beta-KT), ACADSB (SBCAD) or HADH2 (MHBD) genes. The latter is located on the X chromosome, accounting for the milder clinical phenotype in females. If beta-KT deficiency is diagnosed early and treated by fasting avoidance and modest protein restriction, ketoacidosis episodes can be prevented and the prognosis is excellent. The role of treatment in SBCAD deficiency remains unclear pending further delineation of its clinical phenotype and pathogenicity, particularly regarding asymptomatic individuals detected by expanded newborn screening. The ineffectiveness of isoleucine restriction in MHBD deficiency is consistent with the additional roles of this multifunctional enzyme in sex steroid and neurosteroid metabolism and its interaction with amyloid-beta peptide.

Complete beta-oxidation of valproate: cleavage of 3-oxovalproyl-CoA by a mitochondrial 3-oxoacyl-CoA thiolase

The beta-oxidation of valproic acid (VPA; 2-n-propylpentanoic acid) was investigated in vitro in intact rat liver mitochondria incubated with (3)H-labelled VPA. The metabolism of [4,5-(3)H(2)]VPA and [2-(3)H]VPA was studied by analysing the different acyl-CoA intermediates formed by reverse-phase HPLC with radiochemical detection. Valproyl-CoA, Delta(2(E))-valproyl-CoA,3-hydroxyvalproyl-CoA and 3-oxovalproyl-CoA (labelled and non-labelled) were determined using continuous on-line radiochemical and UV detection. The formation of these intermediates was investigated using the two tritiated precursors in respiratory states 3 and 4. Valproyl-CoA was present at highest concentrations under both conditions. Two distinct labelled peaks were found, which were identified as (3)H(2)O and [4,5-(3)H(2)]3-oxo-VPA. The formation of (3)H(2)O strongly suggested that VPA underwent complete beta-oxidation and that [4,5-(3)H(2)]3-oxo-VPA was formed by hydrolysis of the corresponding thioester. The hypothesis that 3-oxovalproyl-CoA undergoes thiolytic cleavage was investigated further. For this purpose a mito chondrial lysate was incubated with synthetic 3-oxovalproyl-CoA, carnitine and carnitine acetyltransferase for subsequent monitoring of the formation of propionylcarnitine and pentanoylcarnitine using electrospray ionization tandem MS. The detection of these compounds demonstrated unequivocally that the intermediate 3-oxovalproyl-CoA is a substrate of a mitochondrial thiolase, producing propionyl-CoA and pentanoyl-CoA, thus demonstrating the complete beta-oxidation of VPA in the mitochondrion. Our data should lead to a re-evaluation of the generally accepted concept that the biotransformation of VPA by mitochondrial beta-oxidation is incomplete.

The clinical phenotype and outcome of mitochondrial acetoacetyl-CoA thiolase deficiency (beta-ketothiolase or T2 deficiency) in 26 enzymatically proved and mutation-defined patients

Mitochondrial acetoacetyl-CoA thiolase (T2 enzyme) deficiency (MIM 203750) is an autosomal recessive disorder of isoleucine and ketone-body metabolism. We determined the molecular basis of T2 enzyme deficiency in 26 patients at the levels of skin fibroblast enzyme activity, protein integrity, and DNA nucleotide sequence. Thirty different disease-associated alleles were identified. From these data we predicted that T2 in 6 of the 26 patients would have a mild effect on the enzyme protein and 20 would have a severe effect from their mutant genotypes. The corresponding clinical data were collected (by interviews and questionnaires) for the patients in the two groups. We found that genotype does not predict clinical severity and mutant sibs can have different clinical phenotypes; there were no consistent differences in clinical severity between patients with null-conferring or residual-conferring genotypes for T2 activity; only the absence of or a low urinary excretion of tiglyglycine during ketoacidosis correlated with a mild genotype. In general, T2 deficiency has a favorable outcome and 23 of 26 patients developed normally; one died during the first ketoacidotic episode and two have developmental delay. The median age at onset for the first ketoacidotic episode is 15 months (range 3 days to 48 months). The frequency of attacks falls with age, the last in our series occurring at 10 years of age; 11 patients had only one episode and 3 patients had none. We conclude that clinical consequences of T2 deficiency are avoidable with early diagnosis, appropriate management of ketoacidosis, and modest protein restriction.

Characterization of N93S, I312T, and A333P missense mutations in two Japanese families with mitochondrial acetoacetyl-CoA thiolase deficiency

Mitochondrial acetoacetyl-CoA thiolase (T2) deficiency is an inborn error of ketone body and isoleucine catabolisms. Japanese patients, GK01 and GK19, were found to be compound heterozygotes of 149delC and A333P, and N93S and I312T, respectively. The latter three missense mutations were individually characterized by analyses of transient expression of the cDNAs and heat stability. A333P and I312T subunits showed aberrant electrophoretic mobility on SDS-PAGE. T2 protein was destabilized by A333P and existed as an insoluble form in the mitochondria. I312T mutation also destabilized T2 protein; however, some T2 protein was retained in soluble form and reduced residual activity was apparent. N93S mutation did not change the heat stability of T2 activity and the reduced residual activity was retained, however a considerable amount was observed in an insoluble form. The effects of mutations were interpreted based on a tertiary structural model of a subunit of the human T2. This model was constructed from the X-ray crystal structure of the homologous peroxisomal 3-ketoacyl-CoA thiolase of Saccharomyces cerevisiae. On the basis of this model, the positions of Ala333 and Ile312 were far from the active site and the mutations would be expected to destabilize the tertiary structure of T2 subunit. By contrast, Asn93 is located near the active site and may function to maintain a local loop structure. The mutation of Asn93 could directly disrupt disposition of the active site.

Two siblings with episodic ketoacidosis and decreased activity of succinyl-CoA:3-ketoacid CoA-transferase in cultured fibroblasts

Succinyl-CoA:3-ketoacid CoA-transferase deficiency leads to a severe ketoacidosis presenting in infancy. We describe two siblings of African ancestry who presented with repeated episodes of ketoacidosis. Both had a positive test for salicylate in the absence of salicylate ingestion. Analysis of urine for organic acids revealed the presence of acetoacetate and 3-hydroxybutyrate. Succinyl-CoA:3-ketoacid CoA-transferase activities in cultured fibroblasts were 11% and 18% of control values.

Investigation, management and therapeutic outcome in 12 cases of childhood and adolescent Cushing's syndrome

OBJECTIVE

Cushing's syndrome in childhood and adolescence is rare. We analysed the clinical presentation, investigation, management and therapeutic outcome in 12 paediatric patients with Cushing's syndrome.

DESIGN

Retrospective review of case notes.

PATIENTS

Twelve patients, 7 males and 5 females, aged 7.6-17.8 years with Cushing's syndrome who were admitted to St Bartholomew's Hospital between 1978 and 1993, were studied. Aetiologies of the Cushing's syndrome patients were: Cushing's disease (9), adrenal adenoma (1), nodular adrenocortical dysplasia (1) and ectopic ACTH syndrome (1). One further male patient, aged 17.8 years who presented with Nelson's syndrome after bilateral adrenalectomy for Cushing's disease in 1978, is described.

MEASUREMENTS

Presenting symptoms, endocrine tests for hypercortisolism, imaging studies, simultaneous bilateral inferior petrosal sinus sampling and therapeutic strategies are discussed.

RESULTS

The dominant clinical features were obesity, short stature, virilization, headaches, fatigue and emotional lability. Investigations confirmed Cushing's syndrome by demonstrating absent cortisol circadian rhythm and impaired suppression on low dose dexamethasone test and differentiated Cushing's disease from other aetiologies by high dose dexamethasone and hCRH tests. In Cushing's disease, pituitary CT scan identified a microadenoma in 4 out of 9 subjects. In 5 of the 9 patients (3 with a normal pituitary CT, 2 with a suggested microadenoma), a pituitary MRI scan was performed and confirmed the CT findings. Inferior petrosal sinus catheterization for ACTH in 4 patients confirmed excess pituitary ACTH secretion, correctly lateralizing the tumour in all cases. Cushing's disease was treated by transsphenoidal surgery alone in 6 patients and combined with pituitary irradiation in 3 patients. Of these 9 patients, 7 are cured and 2 are in remission. The patient with Nelson's syndrome is cured after total hypophysectomy.

CONCLUSIONS

This series describes the clinical features, aetiologies and management of juvenile Cushing's syndrome. Investigation with low and high-dose dexamethasone suppression tests and hCRH test identified the aetiology in each case. Collaboration between paediatric and adult endocrine units together with an experienced neurosurgeon and a radiotherapist contributed to the successful therapeutic outcome of these patients.

Molecular basis of beta-ketothiolase deficiency: mutations and polymorphisms in the human mitochondrial acetoacetyl-coenzyme A thiolase gene

beta-Ketothiolase deficiency is a deficiency in mitochondrial acetoacetyl-CoA thiolase (T2). We present here an update on mutations and polymorphisms in the human T2 gene. No large deletion or insertion has been observed in Southern blot analysis. Seventeen mutations were identified in 13 T2-deficient patients: nine missense, one nonsense, and five splice-site mutations, and two small deletions. Two polymorphic base substitutions were also detected. A common mutation in T2 deficiency has not been detected but 4 mutations (N158D, Q272X, 828 + 1, 1163 + 2) were identified in two independent families. Eleven of 25 mutant alleles identified caused aberrant splicing. In vivo expression analysis of 13 mutant cDNAs using a Lipofectin reagent suggested that T297M, A301P, A380T mutant alleles retain 5-10% normal T2 activity. A correlation between clinical phenotype and genotype in T2 deficiency seems unlikely.

Molecular, biochemical, and clinical characterization of mitochondrial acetoacetyl-coenzyme A thiolase deficiency in two further patients

The molecular basis of mitochondrial acetoacetyl-CoA thiolase (T2) deficiency was studied in two patients (GK11 and GK16). Fibroblasts from each patient had detectable immunoreactive T2 polypeptide (CRM). In pulse-chase experiments, fibroblasts from GK11 had two types of CRM: one (type I CRM) disappeared after a 24-hr chase and migrated more slowly than that of the normal control; the other (type II CRM) was detected with a small amount even after a 72-hr chase and had normal electrophoretic mobility. GK16's fibroblasts had a CRM (type III) which was also detectable even after a 72-hr chase and showed a slower mobility than type I CRM. By analyzing amplified cDNA and genomic fragments, we showed that both patients are genetic compounds; GK11 for the mutations N158D and T297M, and GK16 for the mutations A301P and IVS8 (+1). Expression analyses confirmed that mutant T2 subunits with N158D, T297M, and A301P correspond to type I, II, and III CRM, respectively. Among them, only the mutant T2 polypeptide with T297M appeared to have a detectable residual activity, in spite of its instability. Cotransfection of two cDNAs containing N158D and T297M suggested that heterotetramer formation reduces residual activity in GK11 cells.

3-Ketothiolase deficiency: a review and four new patients with neurologic symptoms

3-Ketothiolase deficiency (3KTD) manifests with intermittent acidosis and is due to deficiency of mitochondrial 2-methylacetoacetate thiolase. Only 22 patients have been previously reported. Although its variable clinical presentation is recognized, the associated neurological findings have not been detailed. We report four new patients all with significant neurological symptoms. Three patients were examined with MRI of the brain which showed increased T2 intensity within the posterior lateral part of the putamen bilaterally. In two the MRI was otherwise normal; in one delayed myelination was also seen. These MRI putaminal findings may be typical enough to suggest the diagnosis of 3KTD. Two of the three had abnormal EEGs; one had an abnormal VEP. 3KTD can thus occur as an organic acidemia associated with encephalopathy.

6-Methyluracil excretion in 2-methylacetoacetyl-CoA thiolase deficiency and in two children with an unexplained recurrent ketoacidaemia

6-Methyluracil (6MU) has been identified in urine collected during acute illness in two children with beta-ketothiolase deficiency (approximately 1 mmol/L) and in two children with recurrent infection-related ketoacidaemia of unknown aetiology (levels of 6.3 and 7.1 mmol/mmol creatinine). Significant amounts of 6MU were not detected in children with fasting ketosis in whom a metabolic disorder was excluded (normal levels less than 25 mumol/mmol creatinine). We propose that the production of 6MU may be related to the accumulation of acetoacetyl-CoA and thus be a marker for disorders where this occurs.

Mitochondrial 2-methylacetoacetyl-CoA thiolase deficiency: an inborn error of isoleucine and ketone body metabolism

A review is presented of 22 published cases of verified or probable mitochondrial 2-methylacetoacetyl-CoA thiolase deficiency, a disorder of isoleucine and ketone body metabolism. The clinical expression, characterized by ketoacidosis, vomiting and lethargy, is highly variable. Typical age of onset is between 6 and 24 months. The disorder, which has been observed in several ethnic groups, is apparently inherited as an autosomal, recessive trait. The prognosis is relatively good if acute episodes of ketoacidosis and dehydration are adequately treated. There is abnormal urinary excretion of 2-methyl-3-hydroxybutyric acid, tiglylglycine, and in some instances also 2-methyl-acetoacetic acid. However, such a pattern of organic aciduria has also been found in cases with normal thiolase activity. Genetic complementation analyses have demonstrated considerable heterogeneity. The cDNA for human methyl-acetoacetyl-CoA thiolase has been cloned and sequenced. Studies in one patient showed a G-to-A substitution at position 1138 of the mRNA, causing 347Ala to Thr change in the mature enzyme. Studies in other patients have shown variable enzyme amount and/or stability.

Molecular studies of mitochondrial acetoacetyl-coenzyme A thiolase deficiency in the two original families

We describe mutations identified in stored skin fibroblast cell lines from two original probands (JB and JM), first reported with 2-methylacetoacetic aciduria, and shown later to have a deficiency of the K(+)-activated enzyme, mitochondrial acetoacetyl-coenzyme A thiolase (T2). JB is homozygous for a 4-base insertion (GCAG) which is derived mutation. The primary mutation is an AG/gt to AG/gc transition at the 5'-splice-junction site in intron 11. An alternative splice site 4 bp downstream (Ggcag/gt) is used which causes a frame shift and replaces 39 C-terminal residues by 70 nonfunctional residues. JM is homozygous for a mutation in the translation-initiation codon (ATG to AAG). By expression analyses the JB mutation (IVS11nt2) causes an unstable T2 polypeptide and the JM mutation (M1K) severely impairs T2 mRNA translation. The JB allele associates with Dutch ancestry (no consanguinity) and the JM allele with Chilean ancestry (distant consanguinity).

Molecular basis of 3-ketothiolase deficiency: identification of an AG to AC substitution at the splice acceptor site of intron 10 causing exon 11 skipping

3-Ketothiolase deficiency (3KTD) is the result of a deficiency in mitochondrial acetoacetyl-CoA thiolase (T2). The molecular basis of 3KTD was analyzed in a patient (GK10) and his family at the protein, cDNA and gene levels. Protein analyses showed that GK10's T2 protein was undetectable in fibroblasts even with the pulse-protein labeling method and that his parents were carriers of 3KTD. Complementary DNA analyses with PCR showed that T2 cDNA in the patient lacked the normal exon 11 sequence and that his parents were obligatory carriers of the DNA sequence which canceled exon 11. When the PCR-amplified genomic fragments around exon 11 were sequenced, an AG to AC mutation at the 3' splice site of intron 10 was detected. This mutation is presumed to be responsible for exon 11 skipping.

Identification of three mutant alleles of the gene for mitochondrial acetoacetyl-coenzyme A thiolase. A complete analysis of two generations of a family with 3-ketothiolase deficiency

3-Ketothiolase deficiency (3KTD) stems from a deficiency of mitochondrial acetoacetyl-coenzyme A thiolase (T2). We analyzed the molecular basis of 3KTD in two generations of a family. A boy (patient 2, GK04), his father (patient 1, GK05), his mother, and his brother were studied; three mutant alleles of T2 gene were identified. Patient 1 is a compound heterozygote: one allele has a point mutation of G to A at position 547 on his T2 cDNA, causing Gly150 to Arg substitution of the mature T2 subunit, and the other allele has GT to TT transition at the 5' splice site of intron 8, causing exon 8's skipping of the T2 cDNA. Patient 2 is also a compound heterozygote: one allele inherited from his mother has AG to CG transition at the 3' splice site of intron 10, causing exon 11's skipping of the T2 cDNA, and the other allele derived from patient 1 has the G to A mutation (Gly to Arg). The brother of patient 2 is an obligatory carrier with the mutant allele causing the exon 8 skipping. This report seems to be the first complete molecular definition of 3KTD at the gene level.

A coupled assay detecting defects in fibroblast isoleucine degradation distal to enoyl-CoA hydratase: application to 3-oxothiolase deficiency

We developed a coupled NaH14CO3 fixation assay to detect 3-oxothiolase deficiency in extracts of cultured human fibroblasts. Cell extracts were incubated with tiglyl-CoA, NAD, CoASH, ATP and NaH14CO3. The enzymatic activities of tiglyl-CoA (enoyl-CoA) hydratase, 2-methyl-3-hydroxybutyryl-CoA dehydrogenase and 2-methylacetoacetyl-CoA thiolase (3-oxothiolase) were coupled to produce propionyl-CoA. Propionyl-CoA produced in the assay was estimated by fixation of NaH14CO3 into [14C]methylmalonyl-CoA employing endogenous propionyl-CoA carboxylase. The control activity was 32 +/- 23 pmol/min per mg protein (+/- 1 S.D., range 7-94; 28 cell lines). Five known cases of 3-oxothiolase deficiency had a mean activity of 2% of the control; a sixth case of 3-oxothiolase deficiency was significantly higher at 27% of the mean control value. Coupled assay activity was also low (3% of control) in the cells from a patient with propionyl-CoA carboxylase deficiency.

Structure and expression of the human mitochondrial acetoacetyl-CoA thiolase-encoding gene

To examine 3-ketothiolase deficiency at the gene level, we analyzed the structure of the human mitochondrial acetoacetyl-CoA thiolase (MAT; EC 2.3.1.9)-encoding gene (MAT). From the genomic library of a normal subject in lambda EMBL3, we isolated seven overlapping clones covering the entire length of MAT and the structural organization was determined. The gene spans approx. 27 kb and contains twelve exons interrupted by eleven introns. The 5'-flanking region of the gene lacks a conventional TATA box, but is G + C-rich and contains two CAAT boxes. Included are a putative binding site for the transcription factor, Sp1, and sequences resembling the binding sites of several other transcription factors, all features characteristic of housekeeping genes. A CAT assay revealed that a 101-bp DNA fragment immediately upstream from the cap site has promoter activity, and suggested that a DNA fragment from bp -888 to -102 probably contains a negative regulatory element(s).

Molecular cloning and sequence of the complementary DNA encoding human mitochondrial acetoacetyl-coenzyme A thiolase and study of the variant enzymes in cultured fibroblasts from patients with 3-ketothiolase deficiency

Complementary DNAs encoding the precursor of human hepatic mitochondrial acetoacetyl-CoA thiolase (T2) (EC 2.3.1.9) were cloned and sequenced. The cDNA inserts in these clones were 1,518 bases in length when overlapped, and encoded the 427-amino acid precursor of this enzyme (45,199 mol wt). This amino acid sequence included a 33-residue leader peptide moiety and a 394-amino acid subunit of the mature enzyme (41,385 mol wt). The T2 gene expression in fibroblasts from four patients with 3-ketothiolase deficiency was analyzed by Northern blotting. The T2 mRNA in all four cell lines had the same 1.7 kb as that of the control. However, the amounts of T2 mRNA differed: the content was reduced in two cell lines (cases 1 and 3), whereas it was within a normal range in others (cases 2 and 4). Pulse labeling followed by subcellular fractionation revealed that the T2 proteins in the fibroblasts from these patients are present in the mitochondria. These results suggest that different mechanisms are involved in the enzyme defects in the four patients.

The biochemical basis of mitochondrial diseases

Dysfunctioning of human mitochondria is found in a rapidly increasing number of patients. The mitochondrial system for energy transduction is very vulnerable to damage by genetic and environmental factors. A primary mitochondrial disease is caused by a genetic defect in a mitochondrial enzyme or translocator. More than 60 mitochondrial enzyme deficiencies have been reported. Secondary mitochondrial defects are caused by lack of compounds to enable a proper mitochondrial function or by inhibition of that function. This may result from malnutrition, circulatory or hormonal disturbances, viral infection, poisoning, or an extramitochondrial error of metabolism. Once mitochondrial ATP synthesis decreases, secondary mitochondrial lesions may be generated further, due to changes in synthesis and degradation of mitochondrial phospholipids and proteins, to mitochondrial antibody formation following massive degradation, to accumulation of toxic products as excess acyl-CoA, to the depletion of Krebs cycle intermediates, and to the increase of free radical formation and lipid peroxidation.

Defect in biosynthesis of mitochondrial acetoacetyl-coenzyme A thiolase in cultured fibroblasts from a boy with 3-ketothiolase deficiency

The etiology of 3-ketothiolase deficiency has been attributed to a defect of mitochondrial acetoacetyl-CoA thiolase because the acetoacetyl-CoA thiolase activity in related materials is not activated by K+, a property characteristic for this enzyme. We studied the enzyme protein and the biosynthesis of mitochondrial acetoacetyl-CoA thiolase, using cultured skin fibroblasts from a 5-yr-old boy with 3-ketothiolase deficiency. The following results were obtained. (a) Activation of acetoacetyl-CoA thiolase activity by K+ was nil; (b) The enzyme activity was not affected by treatment with the antibody against mitochondrial acetoacetyl-CoA thiolase; (c) A signal for mitochondrial acetoacetyl-CoA thiolase protein was not detected in the immunoblot analysis; and (d) Pulse-chase experiments of skin fibroblasts, using [35S]methionine, revealed no incorporation of radioactivity into this enzyme. Therefore, fibroblasts from this patient lacked mitochondrial acetoacetyl-CoA thiolase protein due to a defect in its biosynthesis.

Medium-chain acyl-CoA dehydrogenase deficiency in two siblings with a Reye-like syndrome

An increasing number of reports indicate that patients with some inherited metabolic diseases may have symptoms resembling those of Reye syndrome. We describe two siblings who developed a Reye-like syndrome at ages 16 and 18 months, respectively, after a viral illness and salicylate therapy. Both had fasting hypoglycemia and hypoketonemia. At the time of the acute episode and after ingestion of a medium-chain triglyceride load, one of them excreted large amounts of abnormal metabolites derived from the omega- and (omega-1)-oxidation of medium-chain fatty acids. Medium-chain acyl-CoA dehydrogenase activity was lower than 20% of control values in fibroblasts from both patients. This enzyme defect should be considered in children with a Reye-like syndrome with these distinctive manifestations.

Treatment of Cushing's disease in childhood and adolescence by transsphenoidal microadenomectomy

Fifteen unselected children and adolescents with Cushing's disease were treated by transsphenoidal exploration and microadenomectomy. In only three patients was radiographic examination of the sella turcica, including computed tomography, useful in indicating the presence and location of a pituitary microadenoma. Transsphenoidal microadenomectomy corrected hypercortisolism in 14 of the 15 patients; no adenoma was detected in one patient, and one required a second operation six months after the first because of incomplete removal of the adenoma. All 14 lost weight and cushingoid stigmata and had normal or catch-up growth (if epiphyses were not fused) and progression of puberty. In one patient, a recurrence was successfully treated by repeat microadenomectomy six years after the first procedure. The low morbidity and failure rate of the procedure, the low recurrence rate, the rapid amelioration of signs of hypercortisolism, and the preservation of pituitary function in the present study support transsphenoidal microadenomectomy as a low-risk approach to the initial treatment of Cushing's disease in childhood and adolescence.

Symptoms and signs in organic acidurias

Organic acidaemias can present with a wide variety of signs and symptoms. A survey of the clinical presentation of the organic acidurias shows that single symptoms are not characteristic or diagnostic. Clinical awareness coupled with appropriate laboratory investigation is required for the correct diagnosis to be reached.

Biochemical investigations on a patient with a defect in cytosolic acetoacetyl-CoA thiolase, associated with mental retardation

A severely mentally retarded boy with two normal siblings was persistently found to excrete elevated amounts of 3-hydroxybutyrate and acetoacetate. Enzyme analysis in cultured fibroblasts revealed a probable deficiency in cytosolic acetoacetyl-CoA thiolase which was about half the control activity with normal mitochondrial thiolase activities. Treatment with reduced dietary fat was initiated and a rapid reduction of the ketosis to biochemical normality was demonstrated. Shortly after initiating dietary treatment he presented with severe gastrointestinal problems and the histological features of colitis cystica superficialis. This appeared to respond to intravenous hydrocortisone therapy with an apparent complete recovery.

Fat-derived fuels during a 24-hour fast in children

We examined the availability of fat-derived fuels in 23 normal children aged 1.9 to 16.7 years who fasted for 24 h. We found a rapid and progressive rise in the blood concentrations of free fatty acids (FFA) and ketones. There was a highly significant negative correlation between the concentrations of beta-hydroxybutyrate (beta OHB) and glucose and also between beta OHB and age. With time, the ratio of beta OHB to acetoacetate (AcAc) progressively increased. We briefly review the vital role of ketones in the adaptation to fasting and point out that qualitative tests of ketones can be misleading. Our results indicate that quantitative determinations are essential in the evaluation of suspected disorders of fuel metabolism and that the results must be interpreted according to the age of the child, the duration of fasting, and the concomitant concentrations of glucose.