Heterozygous carriers of succinyl-CoA:3-oxoacid CoA transferase deficiency can develop severe ketoacidosis

Clinical and bi-genomic DNA findings of patients suspected to have mitochondrial diseases

Background: Mitochondrial diseases are the most common group of inherited metabolic disorders, causing difficulties in definite diagnosis due to clinical and genetic heterogeneity. Clinical components are predominantly associated with pathogenic variants shown in nuclear or mitochondrial genomes that affect vital respiratory chain function. The development of high-throughput sequencing technologies has accelerated the elucidation of the genetic etiology of many genetic diseases that previously remained undiagnosed. Methods: Thirty affected patients from 24 unrelated families with clinical, radiological, biochemical, and histopathological evaluations considered for mitochondrial diseases were investigated. DNA isolated from the peripheral blood samples of probands was sequenced for nuclear exome and mitochondrial DNA (mtDNA) analyses. MtDNA sequencing was also performed from the muscle biopsy material in one patient. For segregation, Sanger sequencing is performed for pathogenic alterations in five other affected family members and healthy parents. Results: Exome sequencing revealed 14 different pathogenic variants in nine genes encoding mitochondrial function peptides (AARS2, EARS2, ECHS1, FBXL4, MICOS13, NDUFAF6, OXCT1, POLG, and TK2) in 12 patients from nine families and four variants in genes encoding important for muscle structure (CAPN3, DYSF, and TCAP) in six patients from four families. Three probands carried pathogenic mtDNA variations in two genes (MT-ATP6 and MT-TL1). Nine variants in five genes are reported for the first time with disease association: (AARS2: c.277C>T/p.(R93*), c.845C>G/p.(S282C); EARS2: c.319C>T/p.(R107C), c.1283delC/p.(P428Lfs*); ECHS1: c.161G>A/p.(R54His); c.202G>A/p.(E68Lys); NDUFAF6: c.479delA/p.(N162Ifs*27); and OXCT1: c.1370C>T/p.(T457I), c.1173-139G>T/p.(?). Conclusion: Bi-genomic DNA sequencing clarified genetic etiology in 67% (16/24) of the families. Diagnostic utility by mtDNA sequencing in 13% (3/24) and exome sequencing in 54% (13/24) of the families prioritized searching for nuclear genome pathologies for the first-tier test. Weakness and muscle wasting observed in 17% (4/24) of the families underlined that limb-girdle muscular dystrophy, similar to mitochondrial myopathy, is an essential point for differential diagnosis. The correct diagnosis is crucial for comprehensive genetic counseling of families. Also, it contributes to making treatment-helpful referrals, such as ensuring early access to medication for patients with mutations in the TK2 gene.

A case of severe acidosis in a 12-month-old: Succinyl-CoA:3-ketoacid-CoA transferase deficiency with OXCT1 gene mutations

Succinyl-CoA:3-ketoacid CoA transferase (SCOT) deficiency is a rare autosomal recessive disorder that results in severe ketoacidosis due to a defect in ketone utilization. We describe a case of a 12-month-old infant presenting with severe metabolic acidosis, ketosis, and hyperammonemia, a combination of symptoms suggestive of an inborn error of metabolism. Genetic testing found our patient had a homozygous variant in the OXCT1 gene, c.1543A>G (p.Met515Val). This was the first identified case of SCOT deficiency at our institution. We share our acute management strategies for initial stabilization in the intensive care unit, as well as our approach to preventing morning ketosis after discharge using uncooked cornstarch.

Succinyl-CoA:3-oxoacid coenzyme A transferase (SCOT) deficiency: A rare and potentially fatal metabolic disease

Succinyl-CoA:3-oxoacid coenzyme A transferase deficiency (SCOTD) is a rare autosomal recessive disorder of ketone body utilization caused by mutations in OXCT1. We performed a systematic literature search and evaluated clinical, biochemical and genetic data on 34 previously published and 10 novel patients with SCOTD. Structural mapping and in silico analysis of protein variants is also presented. All patients presented with severe ketoacidotic episodes. Age at first symptoms ranged from 36 h to 3 years (median 7 months). About 70% of patients manifested in the first year of life, approximately one quarter already within the neonatal period. Two patients died, while the remainder (95%) were alive at the time of the report. Almost all the surviving patients (92%) showed normal psychomotor development and no neurologic abnormalities. A total of 29 missense mutations are reported. Analysis of the published crystal structure of the human SCOT enzyme, paired with both sequence-based and structure-based methods to predict variant pathogenicity, provides insight into the biochemical consequences of the reported variants. Pathogenic variants cluster in SCOT protein regions that affect certain structures of the protein. The described pathogenic variants can be viewed in an interactive map of the SCOT protein at https://michelanglo.sgc.ox.ac.uk/r/oxct. This comprehensive data analysis provides a systematic overview of all cases of SCOTD published to date. Although SCOTD is a rather benign disorder with often favourable outcome, metabolic crises can be life-threatening or even fatal. As the diagnosis can only be made by enzyme studies or mutation analyses, SCOTD may be underdiagnosed.

Characterization and outcome of 11 children with non-diabetic ketoacidosis

OBJECTIVES

To study the clinical and laboratory features, management, and outcome of pediatric non-diabetic ketoacidosis (NDKA).

METHODS

Between May 2018 and April 2020, we prospectively collected children under 18 years who presented with ketoacidosis, defined as ketosis (urinary ketones ≥++ and/or serum β-hydroxybutyrate level ≥3 mmol/L) and metabolic acidosis (pH <7.3 and HCO₃ ^- <15 mmol/L). Children with HbA1c level ≥6.5% at initial presentation and those meeting the diagnostic criteria for DM during follow-up were excluded. Data were collected on demographics, clinical and laboratory features, management, and outcome.

RESULTS

Eleven children with 19 episodes of NDKA were identified. The median age was 12 months (range from 5 months to 5 years). They manifested dehydration and disturbed conscious level (all cases), convulsions (n=6), hypoglycemia (n=6), hyperglycemia (n=2) and significant hyperammonemia (n=4). Most cases required intensive care management. Death or neurodevelopmental impairment occurred in six cases. Seven cases had inborn errors of metabolism (IEMs). Other cases were attributed to starvation, sepsis, and salicylate intoxication.

CONCLUSIONS

This is the largest case series of pediatric NDKA. Ketoacidosis, even with hyperglycemia, is not always secondary to diabetes mellitus. IEMs may constitute a significant portion of pediatric NDKA. Increased awareness of this unfamiliar condition is important for prompt diagnosis, timely management, and better outcome.

Cardiac Complications of Propionic and Other Inherited Organic Acidemias

Clinical observations and experimental studies have determined that systemic acid-base disturbances can profoundly affect the heart. A wealth of information is available on the effects of altered pH on cardiac function but, by comparison, much less is known about the actions of the organic anions that accumulate alongside H⁺ ions in acidosis. In the blood and other body fluids, these organic chemical species can collectively reach concentrations of several millimolar in severe metabolic acidoses, as in the case of inherited organic acidemias, and exert powerful biological actions on the heart that are not intuitive to predict. Indeed, cardiac pathologies, such as cardiomyopathy and arrhythmia, are frequently reported in organic acidemia patients, but the underlying pathophysiological mechanisms are not well established. Research efforts in the area of organic anion physiology have increased dramatically in recent years, particularly for propionate, which accumulates in propionic acidemia, one of the commonest organic acidemias characterized by a high incidence of cardiac disease. This Review provides a comprehensive historical overview of all known organic acidemias that feature cardiac complications and a state-of-the-art overview of the cardiac sequelae observed in propionic acidemia. The article identifies the most promising candidates for molecular mechanisms that become aberrantly engaged by propionate anions (and its metabolites), and discusses how these may result in cardiac derangements in propionic acidemia. Key clinical and experimental findings are considered in the context of potential therapies in the near future.

A Rare Cause of Life-Threatening Ketoacidosis: Novel Compound Heterozygous OXCT1 Mutations Causing Succinyl-CoA:3-Ketoacid CoA Transferase Deficiency

Succinyl-CoA:3-ketoacid CoA transferase (SCOT) deficiency is a rare inborn error of ketone body utilization, characterized by episodic or permanent ketosis. SCOT deficiency is caused by mutations in the OXCT1 gene, which is mapped to 5p13 and consists of 17 exons. A 12-month-old girl presented with severe ketoacidosis and was treated with continuous renal replacement therapy. She had two previously unrecognized mild-form episodes of ketoacidosis followed by febrile illness. While high levels of ketone bodies were found in her blood and urine, other laboratory investigations, including serum glucose, were unremarkable. We identified novel compound heterozygous mutations in OXCT1:c.1118T>G (p.Ile373Ser) and a large deletion ranging from exon 8 to 16 through targeted exome sequencing and microarray analysis. This is the first Korean case of SCOT deficiency caused by novel mutations in OXCT1, resulting in life-threatening ketoacidosis. In patients with unexplained episodic ketosis, or high anion gap metabolic acidosis in infancy, an inherited disorder in ketone body metabolism should be suspected.