Analysis of the clinical phenotype and genotype features of 5 cases of beta-ketothiolase deficiency

Abstract

Background

Beta-Ketothiolase deficiency (BKTD) is a rare congenital inherited metabolic disorder associated with defects in the catabolism of isoleucine. This article introduces the clinical phenotypes and genetic variation characteristics of 5 pediatric patients with BKTD.

Results

We retrospectively analyzed the clinical manifestations, laboratory parameters and genetic testing data of 5 pediatric patients with BKTD treated at Beijing Children’s Hospital from April 2018 to October 2024. Among the 5 patients, 4 were male and 1 was female. Their ages of diagnose ranged from 6 months to 1 year and 10 months, with a median age of 9 months. The main clinical manifestations included lethargy, tachypnea, vomiting, respiratory failure, severe metabolic acidosis, and elevated ketone bodies in blood and urine after infection. The levels of 3-hydroxybutyrylcarnitine, 3-hydroxyisovalerylcarnitine, and tiglylcarnitine in the blood were elevated, reaching 2.3 to 18.1 times, 2.3 times, and 2.7 to 5.3 times the upper limits of normal, respectively. The levels of 2-methyl-3-hydroxybutyrate in urine were elevated in all 5 patients, reaching 5.3 to 80.5 times the upper limit of normal. Meanwhile, 3 patients had elevated levels of tiglylglycine and 2-methylacetoacetate in urine. Among the 5 patients, patients 1, 2, and 5 carried three previously unreported missense variations: c.439G > T (p.Val147Leu), c.193 A > T (p.Thr65Ser), and c.224 C > A (p.Ala75Asp). Patients 2 and 3 carried the splice site variation c.1163 + 5G > C and the frameshift variation c.552_555del, respectively, both of which were previously unreported. After clinical diagnosis of BKTD, the patients were given a low-protein, high-carbohydrate, low-fat diet, supplemented with L-carnitine, vitamins B1 and B2. The follow-up time ranged from 4 months to over 6 years. One patient still experienced 1 to 2 episodes of mild metabolic acidosis annually due to non-adherence to dietary management and infections, but none of the patients had severe metabolic crises.

Conclusions

BKTD is a rare disease primarily caused by variations in the ACAT1 gene. The Onset triggers, symptoms, and lab results varied widely among patients. This study not only reported new genetic findings but also stressed the importance about recognizing BKTD in infants and toddlers with non-diabetic ketoacidosis. Early acute care and sustained follow-up secure better outcomes.

Background

Beta-Ketothiolase Deficiency (BKTD), also known as mitochondrial acetoacetyl-CoA thiolase deficiency, is a rare autosomal recessive genetic disorder. Due to pathogenic variations in the ACAT1 gene, patients with BKTD have reduced beta-ketothiolase activity, leading to impaired metabolism of isoleucine and ketone bodies. This results in the accumulation of acidic metabolic intermediates, including 2-methylacetoacetate, 2-methyl-3-hydroxybutyrate, and methylcrotonylglycine, in tissues and the bloodstream [1]. These patients exhibit a wide range of clinical manifestations. During inter-episodes, they may show no significant clinical symptoms, while during acute episodes, they may suffer from recurrent severe ketoacidosis, accompanied by vomiting, dehydration, tachypnea, and even coma and respiratory and circulatory failure. Common triggers for these episodes include prolonged fasting, infections, and high intake of lipids or proteins. In previous literature reports, the variation sites of the ACAT1 gene in BKTD patients have also shown diverse characteristics [2]. This article aims to deepen the understanding of this disease and improve the ability to recognize and treat it clinically by analyzing the clinical phenotypes and genetic variations of 5 BKTD patients.

Methods

We collected the medical records and laboratory tests of 5 pediatric patients diagnosed with BKTD at the Department of Endocrinology and Metabolic Genetics, Beijing Children’s Hospital, Capital Medical University, from April 2018 to October 2024. The diagnosis was confirmed based on clinical symptoms, blood acylcarnitine profiling, urinary organic acid analysis, and genetic testing. Follow-up was also conducted. This study was reviewed and approved by the Ethics Committee of Beijing Children’s Hospital, Capital Medical University, and informed consent for clinical research was obtained.

Venous blood was collected and spotted onto dried blood filter paper. After thorough drying, the levels of amino acids and acylcarnitines in the blood were measured using a tandem mass spectrometer (API200MD™ Triple Quadrupole Mass Spectrometer from ABI, USA). This included the concentrations of tiglylcarnitine (C5:1), 3-hydroxybutyrylcarnitine (C4OH), and 3-hydroxyisovalerylcarnitine (C5OH), among others. For urine analysis, fresh urine samples were collected and prepared by various steps and analyzed using a gas chromatography–mass spectrometry (GC-MS) system (GC-MSQP2020 Ultra from Shimadzu, Japan) to measure the concentrations of urinary metabolites. The urinary GC-MS metabolic screening method established by Matsumoto & Kuhara [3], which provides a detailed description of the protocol. Data analysis was performed using a computer-assisted program, with peaks corresponding to urinary metabolite profiles in the Total Ion Chromatogram (TIC) identified from individual mass spectra. A semi-automatic qualitative analysis was performed on component peaks. As was previously reported [4], the detection level of each component in the tested sample was evaluated based on the ratio of the peak detection area of Q-ion to the intrinsic Creatinine peak area of the sample itself. Tiglylglycine, 2-Methyl-3-Hydroxybutyric acid and 2-Methylacetoacetic acid were tested as biomarkers of BKTD.

The children’s venous blood was collected and sent to a third-party genetic company for whole-exome sequencing.The analysis focused on known and well-established genetic variations related to hereditary diseases, and parental samples were also tested for validation.Sanger sequencing was used to validate the potentially pathogenic genes identified.The variations were checked against disease databases such as ClinVar, GnomAD, and HGMD to see if they had been reported.The variants were classified according to the 2015 ACMG Standards and Guidelines for the Interpretation of Sequence Variants.

Results

Clinical data of the patients

Among the 5 children with BKTD, one of them was of Mongolian ethnicity and the other four children were of Han ethnicity. Their places of origin included Inner Mongolia (1 case), Hebei (2 cases), Shandong (1 case), and Beijing (1 case). The detailed clinical data are shown in Table 1. The age of onset ranged from 2 months to 10 months, with a median age of onset at 6 months. There were 4 males and 1 female, all from different families. The parents were not consanguineous, and there were no significant family histories or abnormal pregnancy histories. The birth weights ranged from 2.8 to 4.3 kg. One child was delivered by cesarean section due to fetal bradycardia during full-term labor, while the other 4 children had no remarkable birth histories. The gross motor development of the children was generally normal. Their ketoacidosis episodes were triggered by respiratory tract infection (3 cases), vaccination (1 case), and insufficient breast milk (1 case). Four children were diagnosed within 2 months after the initial onset, while 1 child was diagnosed 1 year after the initial onset. The clinical manifestations varied among the children (Table 1). All 5 children had severe metabolic acidosis during the acute phase, with positive urinary ketones. Three children had l hypoglycemia, while 2 children had hyperglycemia. Four children (cases 2–5) had a history of invasive mechanical ventilation (for 2–4 days). The brain MRI of child 3 showed symmetrical abnormal signals in the cerebral peduncle, aqueduct of the midbrain, and globus pallidus, suggesting the possibility of metabolic encephalopathy (Fig. 1a and b). After treatment, the symptoms and biochemical indicators of all 5 children were improved significantly.

Table 1.

Clinical characteristics of 5 children with BKTD

Case	Gender	Age at Onset	Age at Diagnosis	Trigger of Onset	Clinical Manifestations	pH	HCO₃⁻ (mmol/L)	BE (mmol/L)	BG (mmol/L)	Urine Ketones	Mechanical Ventilation
1	Female	7 months 25 days	9 months 10 days	Respiratory Infection	Poor mental response, respiratory distress, wheezing	7.1	3.7	−22.8	3.66	2+	No
2	Male	9 months 15 days	9 months 26 days	Vaccination	Poor mental response, respiratory distress, altered consciousness	7.06	3	−27.5	13.4	4+	4 days
3	Male	6 months 5 days	6 months 14 days	Insufficient Breast Milk	Weakness, vomiting, respiratory distress	7.189	2.5	−25.8	4	1+	3 days
4	Male	2 months	6 months	Pneumonia (Mycoplasma, Respiratory Syncytial Virus)	Cough, wheezing, respiratory distress	7.03	5.7	−26	19.4	3+	3 days
5	Male	10 months	1 year 10 months	Respiratory Infection	Wheezing, respiratory distress, vomiting	7.018	6.2	−25.8	3.2	3+	3 days

BE base excess, BG blood glucose

Fig. 1.

a and b the brain T2 weighted MRI of child 3: symmetrical abnormal signals in the cerebral peduncle, aqueduct of the midbrain, and globus pallidus

Tandem mass spectrometry and urine gas chromatography-mass spectrometry

All 5 children underwent blood acylcarnitine profiling and urine organic acid analysis during the acute phase, and the results are shown in Table 2. Tandem mass spectrometry of blood revealed significantly elevated levels of C5:1 in two children (cases 4 and 5, 2.7 to 5.3 times the normal upper limit). Four children had elevated levels of C4OH (cases 1, 3, 4 and 5, 2.3 to 18.1 times the normal upper limit), and one child had elevated levels of C5OH (cases 4, 2.3 times the normal upper limit). Urine gas chromatography-mass spectrometry showed elevated levels of 2-methyl-3-hydroxybutyrate in all five children, ranging from 5.3 to 80.5 times the normal upper limit. Additionally, three children had elevated levels of tiglylglycine and 2-methylacetoacetate in urine (cases 2, 4, and 5). After treatment, the relevant indicators in the blood and urine of all 5 children decreased significantly and even returned to the normal range.

Table 2.

Plasma acylcarnitine profiles and urinary organic acids in 5 patients with BKTD

Case	Acyl carnitine in Blood			Urinary organic acids
	C4OH (µmol/L)	C5OH (µmol/L)	C5:1 (µmol/L)	2-Methyl-3-hydroxybutyrate	Tiglylglycine	2-Methylacetoacetate
1	*0.56	0.074	0.009	*1.0366	0	0
2	0.24	0.05	0.01	*1.0023	*0.0262	*0.0864
3	*0.68	0.07	0.01	*0.5254	0	0
4	*4.348	*0.939	*0.686	*8.0475	*2.3704	*0.0069
5	*1.059	0.107	*0.187	*5.324	*0.2622	*0.0965

*for above the upper limit of normal; lood tandem mass spectrometry detection indicators: Reference range for for C4OH is 0–0.24 µmol/L, for C5OH is 0–0.4 µmol/L, and C5:1 is 6months to 1 year:0–0.13 µmol/L and 1 year to 3 years:0–0.007.007; Urinary organic acids: The reference value for 2-methyl-3-hydroxybutyrate is 0.10, for tiglylglycine is 0.001, and for 2-methylacetoacetate is 0.001; Urinary organic acids are given as ratios, so there is no unit

Genetic findings

After high-throughput sequencing and Sanger validation, a total of 10 variations in the ACAT1 gene were identified in the 5 children with BKTD, including 6 missense variations, 1 nonsense variation, 1 splice site variation predicted to affect splicing by PP3spliceAI, 1 frameshift variation and 1 in-frame variation (Table 3 and Fig. 2). All 5 children carried compound heterozygous variants, and all variants were inherited from their parents. Three novel missense variants: c.439G > T (p.Val147Leu), c.193 A > T (p.Thr65Ser), and c.224 C > A (p.Ala75Asp), one novel frameshift variation c.552_555del (p.Thr185MetfsTer19), and one novel variation c.1163 + 5G > C were identified, the pathogenicity of these variants were shown in Table 3. The variation c.1163 + 5G > C was classified as a VUS (PM2 + PP3): its frequency in the normal population database was 0, and the PP3 spliceAI prediction value was 0.9, indicating effects on splicing (Fig. 3).

Table 3.

Software-based predictions of the effects of ACAT1 variants in 5 patients with BKTD

Case	Nucleotide Variation(Paternal, Maternal)	Amino Acid Variation (Paternal, Maternal)	ACMG Classification	SIFT	SIFT_Predict	PolyPhen_2	PolyPhen_2_Predict	MutationTaster_Predict	REVEL_score	Earlier report on the mutation
1	c.163T > A	p.Phe55Ile	Uncertain	0.035	Damaging	0.929	Probably_damaging	Damaging	0.802	(18)
	c.439G > T	p.Val147Leu	Uncertain	0.066	Tolerated	0.032	Benign	Damaging	0.721	-
2	c.1633 + 5G > C	?	Uncertain	-	-	-	-	-	-
	c.193 A > T	p.Thr65Ser	Uncertain	0.42	Tolerated	0.21	Benign	Damaging	0.489	-
3	c.552_555del	p.Thrl158MetfsTer19	Likely Pathogenic	-	-	-	-	-	-	-
	c.623G > A	p.Arg208Gln	Likely Pathogenic	0.001	Damaging	0.985	Probably_damaging	Damaging	0.862	(12)
4	c.622 C > T	p.Arg208Ter	Pathogenic	-	-	-	-	Damaging	-	(17)
	c.254_256del	p.Glu85del	Uncertain	-	-	-	-	-	-	(19)
5	c.224 C > A	p.Ala75ASP	Pathogenic	0	Damaging	0.993	Probably_damaging	Damaging	0.951	-
	c.655T > C	p.Tyr219His	Pathogenic	0	Damaging	1	Probably_damaging	Damaging	0.948	(20)

Fig. 2.

Schematic illustration and functional domain of human ACAT1 gene showing the location of variants carried by 5 patients. Description of variants follows the HGVS nomenclature. Thiolase_N and Thiolase_C were highlighted differently in pink and orange

Fig. 3.

Splice pattern of variation c.1163 + 5G > C. Exons (boxes) and introns (lines) are numbered according to NCBI refseq: NG009888.1. Shaded boxes denote the untranslated region

Treatment and follow-upThree children (cases 2–4) were treated with invasive mechanical ventilation, and one child (case 1) was treated with nasal cannula oxygen. Management comprised acidosis correction, fluid resuscitation, and maintenance of electrolyte homeostasis according to blood gas analysis and biochemical results. Antibiotic therapy was administered according to the underlying causes of the disease. During the acute phase, child 4 was also given supportive treatment with albumin and packed red blood cells. After clinical diagnosis of BKTD, the diet was adjusted to low protein (1–2 g/kg/day), high carbohydrate, and low fat. L-carnitine was supplemented to regulate metabolism, and energy and nutritional support were provided with vitamins B1 and B2. All children showed improvement and were discharged from the hospital. Follow-up time ranged from 4 months to over 6 years. Child 5 did not strictly adhere to the dietary management and still experienced 1 to 2 episodes of mild metabolic acidosis in one year annually. They were mainly triggered by respiratory or gastrointestinal infections. The condition improved after active fluid resuscitation and treatments targeting the underlying cause. All five children experienced no further episodes of severe metabolic crisis. The oldest child among cases is case 1, a girl of 7 years and 10 months old in the school-age period, with normal intellectual and physical development. No developmental delay was detected in three patients (cases 2, 4, 5; ages 10 months–3.5 years). Reduced limb muscle strength and impaired neuromotor function were documented in Case 3. Despite early neuromotor deficits, case 3 demonstrated substantial developmental recovery at 10-month follow-up (4 months after discharge), with the ability to stand, crawl, and vocalize.

Discussion

BKTD is an autosomal recessive disorder caused by variations in the ACAT1 gene. The incidence of the disease is approximately 1/200,000 to 1/300,000. To date, over 200 cases of BKTD have been reported worldwide, with no racial differences in incidence [5]. Due to the lack of symptoms during inter-episodes and the rapid progression of acute episodes, there may be underdiagnosis of asymptomatic patients and patients with atypical symptoms. In this study, the triggers in our 5 patients aligned with those commonly reported in the literature [6, 7]. In this study, two patients only had elevated C4OH and urinary 2-methyl-3-hydroxybutyrate, without elevated C5:1, C5OH, or urinary tiglylglycine and 2-methylacetoacetate. This atypical blood acylcarnitine profile and urine organic acid test results are rarely reported in previous literature [8]. In addition, 60% of the variations detected in this study were missense variations. Only one patient carried c.622 C > T (p.Arg208Ter), which do not match the common variations 1124 A > G (p.Asn375Ser) and c.622 C > T (p.Arg208Ter) carried by the Chinese population [9]. This discrepancy probably stems from the study’s sample size. By describing the clinical and genetic heterogeneity of the 5 BKTD patients diagnosed in our center, this study expands the understanding of the disease and helps improve the diagnostic and therapeutic level for this condition.

During the metabolism of isoleucine, 2-keto-3-methylvalerate is first generated by the action of transaminase. It is then gradually converted into 2-methylacetyl-CoA through the action of branched-chain ketoacid dehydrogenase, isovaleryl-CoA dehydrogenase, and other hydrolases and dehydrogenases. Beta-Ketothiolase catalyzes the final step of isoleucine metabolism by cleaving 2-methylacetyl-CoA into the metabolic products acetyl-CoA and propionyl-CoA. Beta-Ketothiolase also catalyzes the interconversion of acetyl-CoA and acetoacetyl-CoA in the mitochondria of hepatic and extrahepatic tissues to complete the metabolism of ketone bodies [10, 11]. Deficiency of Beta-ketothiolase activity leads to the accumulation of intermediate metabolites of isoleucine metabolism, typically manifested in the blood as elevated concentrations of C5OH, C4OH, and C5:1. In gas chromatography-mass spectrometry of urine, elevated levels of 2-methyl-3-hydroxybutyrate, tiglylglycine, and 2-methylacetoacetate are also observed. In this study, patients 1 and 3 only had elevated C4OH and urinary 2-methyl-3-hydroxybutyrate, with no increase in C5:1, C5OH, or urinary tiglylglycine and 2-methylacetoacetate. In previous literature, patients with the c.431 A > C (p.His144Pro)variation retain partial Beta-ketothiolase activity, and in severe ketoacidosis, C5-OH and C5:1 remain within the normal range, with only a mild increase in urinary 2-methyl-3-hydroxybutyrate levels [8]. Patient 1 carried the compound heterozygous variations c.163T > A (p. Phe55Ile) and c.439G > T (p. Val147Leu). The c.163T > A (p.F55I) variation was previously reported and classified by ACMG as a variant of uncertain significance (Table 3). Our analysis revealed a novel c.439G > T variant leading to p.Val147Leu. The prediction results from SIFT, PolyPhen-2, and REVEL for c.439G > T (p.V147L) suggested that it was likely pathogenic, and Variation Taster predicted it to be pathogenic. ACMG classified it as a variant of uncertain significance (PM2 + PP3). This variant lies close to the reported c.431A>C site. Patient 3 carried two compound pathogenic variants c.552_555del (p.Thrl158MetfsTer19) and c.623G > A (p.Arg208Gln). The c.623G > A (p. Arg208Gln) variant was previously reported but yielded no residual Beta-ketothiolase activity while c.552_555del (p. Thrl158MetfsTer19) was an unreported variant [12]. Further studies were needed to explain these atypical blood acylcarnitine and GC-MS results.

The ACAT1 gene is located on chromosome 11q22.3–23.1.1, spanning a 27-kb genomic region and comprising 12 exons and 11 introns. Prior studies identified 1124 A > G (p.Asn375Ser) and c.622 C > T (p.Arg208Ter) as frequent variants in Chinese cohorts [9]. In a study by Nguyen et al. from 2005 to 2016, which included 41 Vietnamese patients with BKTD, 85% of the population carried the c.622 C > T and c.1006-1G > C variants. The c.622 C > T variant was the most common in the Vietnamese population and has also been reported in Dutch and American populations [1, 13]. In India, the incidence of BKTD was approximately 1 in 111,000, with c.578T > G (p.Met193Arg) being the primary variant site, occurring at a frequency of about 50% [14]. In other populations, ACAT1 gene variants were relatively diverse. In this study, all 5 Chinese patients included carried ACAT1 gene variants, which did not match the high-frequency variants in the populations, likely due to the small sample size. In this study, only one patient carried c.622 C > T (p. Arg208Ter) and 60% of the detected variations were missense variations, including three novel variants: c.439G > T (p. Val147Leu), c.193 A > T (p. Thr65Ser), and c.224 C > A (p. Ala75Asp). The c.224 C > A (p. Ala75Asp) variant was predicted to be pathogenic by the REVEL protein prediction software. One novel frameshift variation led to a change in the 208th amino acid from arginine to glutamine, potentially causing loss of gene function. The c.1163 + 5G > C variation was classified as a variant of uncertain significance (PM2 + PP3) with a PP3spliceAI prediction value of 0.92, indicating an impact on splicing and possibly affecting protein conformation. Among the 5 patients reported in this study, except for patients 3 and 5 who carried ACAT1 compound heterozygous variants classified as pathogenic or likely pathogenic, the remaining patients carried variants of uncertain significance. In our current study, clinical presentation and metabolic biomarkers were consistent with BKTD in all patients. However, definitive confirmation of variant pathogenicity requires functional genetic analysis.

Acute episodes of BKTD can occur in individuals of all ages but are most first seen in infants aged 6 to 24 months. In the absence of Beta-ketothiolase activity, mitochondrial medium-chain 3-ketoacyl-CoA thiolase can partially compensate for the metabolic role of Beta-ketothiolase in ketone body metabolism [7]. Metabolic crises caused by BKTD only occur when decompensation is triggered by risk factors such as infection, fasting, or excessive protein intake. In infants under 6 months of age, protective maternal immunoglobulins, regular feeding, and the relatively low protein content in breast milk and formula reduce the risk of decompensation [7]. As children grow older, their increased glycogen storage capacity also helps to prevent the occurrence of metabolic acidosis [1]. Patients develop severe non-diabetic ketoacidosis during acute BKTD crises, often accompanied by recurrent vomiting, dehydration, and dyspnea. Glucose homeostasis can be disrupted during acute episodes, presenting as either hypoglycemia or hyperglycemia. In this study, 3 of the 5 children had hypoglycemia, while 2 had elevated blood glucose levels during the acute phase, with the highest venous blood glucose level reaching 19.4 mmol/L. The occurrence of hyperglycemia may be related to a stress response, and it is important to differentiate it from diabetic ketoacidosis. Differentiation points include the precipitating factors, the presence of a history of diabetes, typical diabetic symptoms such as polydipsia, polyuria, and weight loss, as well as auxiliary test results such as glycated hemoglobin, insulin, and C-peptide levels.

In addition to the typical symptoms, some children may present with neurological symptoms such as epilepsy and limb movement disorders. Previous literature has reported that approximately 20% of BKTD patients experience neurological sequelae [6]. Typical brain MRI findings include widespread white matter demyelination and symmetric hyperintensities in the basal ganglia on T2 imaging. In a study by Nguyen et al., 4 out of 28 BKTD patients who underwent MRI showed T2 hyperintensities in the basal ganglia or hypodensity in the posterior limb of the internal capsule [7]. In this study, patient 3 had symmetric abnormal signals in the cerebral peduncle, aqueduct of the midbrain, and globus pallidus on brain MRI, and mental and neuromotor assessments indicated reduced muscle strength in the limbs and poor neuromotor function. Previous literature speculated that these neurological injuries might be related to severe metabolic acidosis or to mitochondrial respiratory chain dysfunction associated with organic acid disorders [15]. In some BKTD patients, clinical neurological deficits occur even in the absence of severe ketoacidosis prior to diagnosis, and in these patients, the accumulation of isoleucine intermediate metabolites may also have a direct neurotoxic effect [16, 17].

Acute episodes of BKTD often occur secondary to inadequate energy intake following gastrointestinal or respiratory infections, when the body is in a state of high consumption [18, 19]. Based on treating the infection-related triggers, it is necessary to actively supplement with a high-carbohydrate diet or intravenous glucose-containing fluids for supportive treatment. In severe cases of ketoacidosis, a low-dose insulin infusion can help correct the ketoacidosis, and appropriately replenishing electrolytes helps to maintain homeostasis [20]. During the acute phase, L-carnitine can be considered to correct metabolic acidosis. During the remission phase, treatment should focus on patient education, with protein intake restricted to 1–2 g/(kg·d), which is the mild protein-restricted diet currently recommended by guidelines and is less stringent than that for other organic acid disorders. A high-calorie, low-fat diet should be provided, fasting should be avoided, and oral L-carnitine supplementation at 100 mg/(kg·d) should be administered. Nguyen et al. followed up with 41 patients for up to 10 years, with 5 deaths, 2 cases of neurological sequelae, and the rest of which (82%) had a good prognosis. However, 43% of patients experienced recurrent metabolic acidosis [7]. In this current study, all 5 patients were discharged after improvement and have had favorable outcome to date. Patient 3, who initially presented with reduced limb muscle strength and poor neuromotor function, showed significant improvement by 10 months of age. Patient 5, who did not strictly adhere to the diet, still experienced 1 to 2 episodes of mild metabolic acidosis annually, triggered by respiratory or gastrointestinal infections. Upon inquiry into the medical history and dietary structure, it was found that the child’s daily intake of protein and fat exceeded the recommended amounts, and thus, dietary management education was reinforced. According to previous literature, there were no clear correlation between the prognosis of BKTD patients and genotype, frequency of episodes, or age at diagnosis. Proper management during the acute phase and long-term follow-up contribute to a favorable prognosis.

Conclusion

BKTD is a rare congenital inherited metabolic disorder primarily characterized by non-diabetic ketoacidosis. In the present study, we identified novel ACAT1 variants in patients with BKTD and expanded the clinical spectrum associated with the disease. However, a key limitation of this study is the lack of functional assays to confirm the pathogenicity of the newly identified ACAT1 variants. Another unneglectable limitation of the study is the small sample size. Therefore, a larger sample size and experimental validation of the new variants are needed.

Abbreviations

BKTD

β-Ketothiolase deficiency

C4OH

3-hydroxybutyrylcarnitine

C5OH

3-Hydroxyisovalerylcarnitine

C5:1

Tiglylcarnitine

GC-MS

Gas chromatography–mass spectrometry

Authors’ contributions

All authors helped to perform the research; Jinglu Jin wrote the manuscript; Di Wu contributed to the project management; Jinglu Jin, Yuan Ding and Di Wu took part in the collection of clinical samples; Yuan Ding conceived and designed the project as well as revised the manuscript. All listed authors revised the paper critically and approved the final version of the submitted manuscript. All authors read and approved the final manuscript.

Funding

Beijing Natural Science Foundation (7234365).

Data availability

All data generated and analyzed during this study are included in this published article and are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

The research protocol was approved by the ethics committee of Beijing Children’s Hospital, Capital Medical University, and was performed in accordance with the Declaration of Helsinki. Written informed consents were received from all the patients’ parents before they are participating in the study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.