Beta-Ketothiolase Deficiency: A Comprehensive Review of Genetic Variants and Pathophysiology

Development of MLPA for human ACAT1 gene and identification of a heterozygous Alu-mediated deletion of exons 3 and 4 in a patient with mitochondrial acetoacetyl-CoA thiolase (T2) deficiency

Beta-ketothiolase (mitochondrial acetoacetyl-CoA thiolase) deficiency is a genetic disorder characterized by impaired isoleucine catabolism and ketone body utilization that predisposes to episodic ketoacidosis. It results from biallelic pathogenic variants in the ACAT1 gene, encoding mitochondrial beta-ketothiolase. We report two cases of beta-ketothiolase deficiency presenting with acute ketoacidosis and "metabolic stroke." The first patient presented at 28 months of age with metabolic acidosis and pallidal stroke in the setting of a febrile gastrointestinal illness. Although 2-methyl-3-hydroxybutyric acid and trace quantities of tiglylglycine were present in urine, a diagnosis of glutaric acidemia type I was initially suspected due to the presence of glutaric and 3-hydroxyglutaric acids. A diagnosis of beta-ketothiolase deficiency was ultimately made through whole exome sequencing which revealed compound heterozygous variants in ACAT1. Fibroblast studies for beta-ketothiolase enzyme activity were confirmatory. The second patient presented at 6 months of age with ketoacidosis, and was found to have elevations of urinary 2-methyl-3-hydroxybutyric acid, 2-methylacetoacetic acid, and tiglylglycine. Sequencing of ACAT1 demonstrated compound heterozygous presumed causative variants. The patient exhibited choreoathethosis 2 months after the acute metabolic decompensation. These cases highlight that, similar to a number of other organic acidemias and mitochondrial disorders, beta-ketothiolase deficiency can present with metabolic stroke. They also illustrate the variability in clinical presentation, imaging, and biochemical evaluation that make screening for and diagnosis of this rare disorder challenging, and further demonstrate the value of whole exome sequencing in the diagnosis of metabolic disorders.

The aim of this study was to explore the genetic features of a family with 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency (MHBDD) which may provide the basis for the diagnosis and genetic counseling. Clinical data of the proband was collected, total RNA and genomic DNA were extracted from the peripheral blood. The whole coding region of the ACAT1 gene was amplified by RT-PCR. 5' noncoding region of the ACAT1 gene and all 6 exons and flanking intron regions of the HADH2 gene were amplified by PCR. All amplification products were directly sequenced and compared with the reference sequence. (1) The patient was a one-year-old boy who presented with psychomotor retardation and astasia when he was admitted to the hospital. Biochemical test revealed slight hyperlactatemia (3.19 mmol/L) and magnetic resonance imaging showed delayed myelination. 2-Methylacetoacetyl-CoA thiolase deficiency was suggested by gas chromatography-mass spectrometry. (2) There was no mutation in the ACAT1 gene and a hemizygous missense mutation c.388C > T was found in the 4 exon of the HADH2 gene which resulted in p. R130C. Proband's mother was the heterozygote and the father was normal. This is the first report on MHBDD patient and HADH2 mutation in China. p.R130C is responsible for the pathogenesis of the disease in the infant.

Deficiency of mitochondrial acetoacetyl-coenzyme A thiolase T2 (methylacetoacetyl-coenzyme A thiolase, MAT) or β-ketothiolase is a rareautosomal recessive disorder that is characterized by ketoacidosis episodes. Outcomes vary from normal development to severe cognitive impairment or even death after an acute episode of ketoacidosis. The classical biochemical profile of T2 deficiency is a result of mutations in both alleles of the ACAT1 gene and comprises characteristic abnormalities in urinary organic acids and blood or plasma acylcarnitine profiles. In this study, we present two sibling cases with quite different clinical properties.

Beta-ketothiolase (BKT) deficiency is a disorder of ketone body metabolism and isoleucine catabolism. Patients with BKT deficiency have intermittent ketoacidosis attacks. In this report, we describe an unusual case that mimicked type 1 diabetes presentation. The patient is a 1-year-old boy who presented with clinical and biochemical evidence of diabetes ketoacidosis (DKA). After the resolution of DKA, he was commenced on subcutaneous insulin regimen. Insulin requirements decline over few weeks to 0.3 U/kg/day, and due to normalization of blood glucose coupled with frequent hypoglycemic episodes, insulin was stopped for few months. Later, he developed two additional DKA episodes with intermittent period of no insulin requirement. At 2 years of age, he presented with ketoacidosis and hypoglycemia. The unusual presentation of ketoacidosis accompanied with hypoglycemia prompted genetic testing. Genetic testing revealed a novel homozygous mutation in the ACAT1 gene. The patient was advised to avoid prolonged fasting and started on a low-protein diet. Since then, he had developed mild episodes of ketosis with illness required intravenous hydration. In conclusion, the pediatrician should maintain a high index of clinical suspicion when dealing with children presenting with unusual diabetic ketoacidosis. Delayed diagnosis of BKT, failure of management of acute crisis, and the unnecessary use of insulin can lead to high morbidity and mortality.

Beta-ketothiolase deficiency is a rare autosomal recessive disorder characterized by an inborn error of isoleucine catabolism and affecting ketone body metabolism. Clinical features characterized by intermittent keto acidotic episodes are associated with clinical signs and symptoms of toxic encephalopathy such as lethargy, hypotonia, vomiting, tachypnea, and coma in some patients, with an onset during infancy or toddler-hood. A two months old girl presented to pediatric ward of Imam Reza Hospital in Mashhad City, Northwestern Iran in October 2016, with acute episode of fever and toxic encephalopathy with attack of vomiting, hypotonia, lethargy, tonic-clonic seizures and then a day in coma, few days after vaccination. After then similar episodes happened until 7 months age. Bio chemical tests that suggested diagnose of beta ketothiolase deficiency were attacks of ketoacidosis with urinary exertion of 2-methyl-3-hydroxybutyric acid 2-methyl aceto acetic acid tiglylglycine. In genetic assessment, we detected a novel homozygous mutation c.664A> C (p. Ser 222 Arg) in ACAT gene. This is the first report of beta ketothiolase deficiency confirmed by molecular analysis from Iran. We report on a homozygous variant in the ACAT1 gene and that is a novel mutation. We recommended carrier testing for all informative family members to recognize mutations in asymptomatic family members.

Acetoacetyl-CoA thiolase deficiency, also known as Beta-ketothiolase deficiency (BKTD), is an autosomal recessive organic aciduria included in the Italian newborn screening (NBS) panel. It is caused by mutations in the ACAT1 gene, which encodes the mitochondrial acetyl-CoA acetyltransferase. Its deficiency impairs the degradation of isoleucine and acetoacetyl-CoA, leading to the accumulation of toxic metabolites. We describe three cases of BKTD. The first newborn showed increase in C5:1, C4DC/C5OH, C3DC/C4OH in the NBS. Urinary organic acids (uOAs) revealed marked excretion of 2-methyl-3-hydroxybutyrate. Tiglylglycine was absent. Genetic testing identified the compound heterozygosity for two pathogenic ACAT1 variants. The second patient showed increased levels of C5:1, C4DC/C5OH, C3DC/C4OH in the NBS. uOAs revealed 2-methyl-3-hydroxybutyrate and tiglylglycine. A homozygous VUS in ACAT1 was identified. The third case showed elevation of C4DC/C5OH, C3DC/C4OH in the NBS, with a slight increase in C5:1. uOAs showed 2-methyl-3-hydroxybutyrate and tiglylglycine. A homozygous missense VUS was identified in the ACAT1 gene. BKTD exhibited variable NBS biochemical phenotypes across the three cases. While C5OH and C5:1, the primary markers, were not consistently elevated in all our cases, C4OH strongly increased in all three. Our findings support the use of C4OH in a combined marker strategy to improve BKTD NBS.

Beta-ketothiolase deficiency (BKTD) is an inborn error of ketone bodies and isoleucine metabolism. Patients with BKTD manifest during late infancy and early childhood with recurrent episodes of ketoacidosis (accumulated acetoacetate and β-hydroxybutyrate) that may be refractory to treatment and life-threatening. BKTD is exaggerated by fasting, starvation and catabolic conditions. Dichloroacetate (DCA) is a safe effective treatment for both lactic acidosis and non-Hodgkin’s lymphoma. DCA is non-toxic and non-carcinogenic at therapeutic doses. DCA toxic doses are hundred times (12- gram/l) more than the therapeutic doses. In experimental models of ketosis, DCA reduces ketonemia and ketonuria while significantly lowering blood glucose. Importantly, DCA was reported to divert pyruvate (amino group acceptor to form alanine in transamination reactions to regenerate α-ketoglutarate from glutamate) to oxidative pathways to form acetyl CoA that is oxidized in Krebs cycle. That inhibits first step of isoleucine catabolism (transamination step) and consequently blocks formation of acetoacetate and β-hydroxybutyrate. That alleviates ketone bodies-induced refractory metabolic acidosis. On biochemical and pharmacological bases, we suggest DCA as a novel evidence-based adjuvant and life-saving treatment for BKTD. Moreover, DCA-induced inhibition of ketone bodies uptake will be alleviated by insulin effects. Causes of refractory metabolic acidosis in BKTD are increased levels of ketone bodies (due to increased isoleucine catabolism, increased ketone bodies formation and decreased ketone bodies utilization). DCA relieves most of these. Biochemically, DCA and ketone bodies (acetoacetate and β-hydroxybutyrate) are structural analogs derived from acetic acid. In neonatology, DCA improved neonatal septicaemia-induced refractory metabolic acidosis that did not respond to conventional sodium bicarbonate. In conclusion, DCA is strongly suggested to treat BKTD.

CRISPR-based adaptive and heritable immunity in prokaryotes

On the basis of strong research evidence, Duchenne muscular dystrophy (DMD), the most common severe childhood form of muscular dystrophy, is an X-linked recessive disorder caused by out-of-frame mutations of the dystrophin gene. Thus, it is classified asa dystrophinopathy. The disease onset is before age 5 years. Patients with DMD present with progressive symmetrical limb-girdle muscle weakness and become wheelchair dependent after age 12 years. (2)(3). On the basis of some research evidence,cardiomyopathy and congestive heart failure are usually seen in the late teens in patients with DMD. Progressive scoliosis and respiratory in sufficiency often develop once wheelchair dependency occurs. Respiratory failure and cardiomyopathy are common causes of death, and few survive beyond the third decade of life. (2)(3)(4)(5)(6)(7). On the basis of some research evidence, prednisone at 0.75 mg/kg daily (maximum dose, 40 mg/d) or deflazacort at 0.9 mg/kg daily (maximum dose, 39 mg/d), a derivative of prednisolone (not available in the United States), as a single morning dose is recommended for DMD patients older than 5 years, which may prolong independent walking from a few months to 2 years. (2)(3)(16)(17). Based on some research evidence, treatment with angiotensin-converting enzyme inhibitors, b-blockers, and diuretics has been reported to be beneficial in DMD patients with cardiac abnormalities. (2)(3)(5)(18). Based on expert opinion, children with muscle weakness and increased serum creatine kinase levels may be associated with either genetic or acquired muscle disorders (Tables 1 and 3). (14)(15)

Mitochondrial acetoacetyl-coenzyme A (CoA) thiolase deficiency is an organic aciduria which affects isoleucine and ketone body catabolism. GK16 (the index patient) was affected with this disorder and previous studies had revealed that GK16 was a compound heterozygote with IVS8(+1) gt to tt and A301P mutations. In a subsequent pregnancy, prenatal diagnosis was performed and the fetus's amniocytes were analysed by the polymerase chain reaction (PCR) followed by the heteroduplex detection method on a Mutation Detection Enhancement gel. The fetus was identified as a carrier of the IVS8(+1) mutation. We confirmed the diagnosis by immunoblot analysis of extracted amniocytes and gene analysis with blood filter paper after delivery. This is the first report of prenatal diagnosis of this disorder at the gene level.

BackgroundBeta-ketothiolase deficiency (mitochondrial acetoacetyl-CoA thiolase, T2) deficiency (OMIM #203750, *607809) is an autosomal recessive disorder of isoleucine catabolism and ketone body utilization. It is caused by mutations in the ACAT1 gene and characterized by intermittent ketoacidosis episodes triggered by ketogenic stresses, with no clinical symptoms between the episodes. Neurological complications, particularly extrapyramidal signs may occur as sequelae of the ketoacidosis episodes but may also occur without or before any apparent metabolic crisis. T2 deficiency is characterized by the accumulation of isoleucine metabolites, 2methylacetoacetate, 2-methyl-3-hydroxybutyrate, and tiglylglycine, detected in urine organic acids and blood acylcarnitines with or without hypoglycemia.MethodsThis study presents data from twelve patients with T2 deficiency, diagnosed between 7 months and 22 months of age at two tertiary care centers in Palestine. The clinical, biochemical, molecular genetic data, and neurological outcomes are reviewed.ResultsWe report on twelve patients (6 females and 6 males) from eight families in four different regions of the West Bank and Gaza Strip. All patients were offspring of consanguineous marriages. Ketoacidotic episodes were the predominant manifestations in all patients, and each episode was triggered by either acute gastroenteritis or upper respiratory infections. One patient initially presented with hypotonia and psychomotor delay, later developing a ketoacidotic episode a few months afterward. The characteristic laboratory finding in all patients was the increased urinary excretion of 2-methyl-3-hydroxybutyrate and tiglylglycine. Ten of the twelve patients had favorable outcomes, while two unfortunately passed away at the time of the study. Molecular genetic analysis of the ACAT1 gene was conducted on nine patients from six families, revealing four different variants, two of which were novel. Additionally, a founder mutation was identified in six patients from three families.ConclusionsThe study underscores the critical role of genetic research in unraveling the complexities of beta-ketothiolase deficiency and related disorders. By identifying haplotype blocks, founder mutations, and novel pathogenic variants, researchers can significantly improve diagnostic precision, enhance genetic counseling, and lay the groundwork for developing targeted therapies. We identified two novel variants and a founder mutation, thereby broadening the genetic spectrum of this rare disease.

To investigate the clinical phenotype and ACAT1 gene mutation in a family affected with beta-ketothiolase deficiency (BKTD). Clinical features and laboratory test data were collected. The probands were monozygotic twin brothers. Genomic DNA was isolated from peripheral blood leukocytes obtained from the probands and their family members. Molecular genetic testing of the ACAT1 gene was carried out. The probands have presented with fever, vomiting and severe ketoacidosis. By arterial blood gas testing, pH was determined to be 7.164, bicarbonate was 4.0 mmol/L, and urine ketone was ++++. Urinary organic acid gas chromatography-mass spectrometry analysis showed excessive excretion of 3-hydroxybutyric acid, 2-methyl-3-hydroxybutyric acid and tiglylglycine. Increased 3-hydroxybutyrylcarnitine (C4-OH), tiglylcarnitine(C5:1) and 3-hydroxyisovalerylcarnitine (C5-OH) levels. The clinical phenotype of proband's parents were both normal, but an elder sister turned out to be an affected patient. Genetic analysis has identified two heterozygous mutations [c.622C>T(p.R208X) and c.653C>T (p.S218F)] in the proband, which were respectively detected in the mother and father. The c.653C>T (p.S218F) mutation was not found among the 100 healthy controls and has not been included in the Human Gene Mutation Database(HGMD). The primary clinical manifestations of BKTD is ketoacidosis. Urine organic acid and blood acylcarnitine analyses play an important role in the diagnosis of the disease. The compound heterozygous of ACAT1 gene mutations probably underlie the BKTD in our patient.

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.

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) and other gene-editing technologies have revolutionized genetic research by enabling precise, targeted modifications of DNA sequences. This paper provides a comprehensive exploration of CRISPR technology, detailing its development, mechanism of action, and versatility in diverse applications. From advancements in medicine, including therapeutic interventions for genetic disorders, to innovations in agriculture aimed at enhancing crop resilience and yield, CRISPR's transformative potential is vast. However, the rapid evolution of gene editing presents significant ethical and societal challenges, particularly concerning human germline editing, ecological impacts, and issues of accessibility and equity. This paper examines these ethical considerations, emphasizing the need for robust regulatory frameworks and responsible scientific practices. It also projects the future trajectory of gene editing technologies, speculating on emerging trends, possible breakthroughs, and the global implications of CRISPR in fields such as personalized medicine, synthetic biology, and biotechnology. By critically analyzing current applications and addressing ethical concerns, this study aims to provide a balanced perspective on CRISPR's potential to reshape genetic research while advocating for ethical governance and public engagement in its ongoing development. CRISPR’s ability to target specific genes with high accuracy has made it an invaluable tool not only in research laboratories but also in clinical settings, where it shows promise in treating previously incurable diseases. Recent advancements have extended CRISPR’s applications beyond simple gene knockout, allowing for base editing, prime editing, and epigenetic modifications that expand the possibilities for genetic correction and enhancement. As scientists explore using CRISPR in complex organisms, the precision and control required for safe and effective treatments become a key focus, particularly in addressing off-target effects that could lead to unintended genetic consequences.