Isobutyryl-coenzyme A dehydrogenase deficiency (IBDD) is a rare inborn error of valine metabolism caused by variants in the ACAD8 gene. Since its initial description in 1998, a wide range of clinical features has been reported, but the disease status and clinical significance of IBDD remain under debate. We systematically studied all published cases of IBDD to provide an overview of the reported phenotype and molecular spectrum. A comprehensive literature review identified 172 individuals with IBDD reported up to December 2024. Seven children were diagnosed following selective screening due to family history or clinical suspicion, while 165 were identified through expanded newborn screening programs. Elevated blood or plasma C4-acylcarnitine was observed universally, and isobutyrylglycinuria was a common but not invariable urinary marker. Of these 172 individuals, 146 were asymptomatic at follow-up, whereas 26 presented with diverse, non-specific manifestations, including motor delay, failure to thrive, muscular hypotonia, speech delay, developmental delay, and anemia-the latter being the most frequently reported abnormality. Biallelic pathogenic variants in ACAD8 were identified in most cases with available genetic information, with c.286G > A p.(Gly96Ser) emerging as the most prevalent variant, predominantly among individuals of Chinese origin. Notably, altered biochemical markers of liver function were reported in 19 individuals, including 18 with isolated elevations of serum transaminases and γ-glutamyl transferase. One 11-year-old boy exhibited hepatomegaly and ultrasound findings suggestive of hepatic steatosis, along with markedly elevated transaminase levels. Hepatic steatosis has also been observed in an IBDD mouse model, suggesting a potential link between IBDD and liver involvement. Most individuals with IBDD remain asymptomatic following detection through newborn screening, yet a minority develop heterogeneous clinical features. Our overview highlights that some liver enzyme abnormalities and hepatic steatosis may occur in some individuals with IBDD. These findings suggest that further research is warranted to clarify possible hepatic implications of IBDD and to determine whether long-term monitoring of affected individuals should be considered, particularly in light of ongoing discussions about the appropriateness of IBDD as a target condition in newborn screening programs.

Organic acid disorders (OADs) are inherited metabolic defects in the enzymes and cofactors involved in metabolic pathways. This systematic review and meta-analysis investigated the incidence and regional differences in OADs between the northern and southern regions of China. Searches of the PubMed, Embase, Web of Science, and Chinese databases (CNKI, Veipu, and Wanfang) revealed 1784 studies indexed between January 2002 and December 2024. After quality assessment and data extraction, the meta-analysis was conducted on OAD screening data from 57 studies involving 13,314,056 newborns and 1501 OAD cases in China. The seven most prevalent OADs were methylmalonic acidemia (MMA), 3-methylcrotonyl-CoA carboxylase deficiency, glutaric acidemia type I, isobutyryl-CoA dehydrogenase deficiency, isovaleric acidemia, 2-methylbutyryl-CoA dehydrogenase deficiency (2-MBD), and propionic acidemia. The meta-analysis revealed an OAD prevalence of 112.38 (95% confidence interval 106.70-118.07) per 1,000,000 newborns. The incidence of OADs and MMA was significantly higher in northern China than in southern China, whereas the incidence of 2-MBD was significantly lower in northern China than in southern China (p < 0.0001). Additionally, the ratio of MMA combined with homocystinuria to MMA was higher in northern China than in southern China (p < 0.05). These results provide valuable epidemiological insights and guidance for newborn screening for OADs in China.

Organic acidemias (OADs) are a group of congenital metabolic disorders whose incidence, disease spectrum, and genetic profiles differ greatly across countries. This study aimed to determine the characteristics of OADs in Quanzhou, China. A total of 693,797 newborns were screened for OADs from 2014 to 2023, and the acylcarnitine and genetic profiles of patients with OADs were analysed. Sixty-nine patients were confirmed to have OADs, with an overall incidence of 1/10,055 newborns. Seven types of OADs were identified, of which 18 were 2-methylbutyryl-CoA dehydrogenase deficiency (MBAD), 18 were 3-methylcrotonyl-CoA carboxylase deficiency (3-MCCD), 13 were glutaric acidemia type 1 (GA-1), nine were isobutyryl-CoA dehydrogenase deficiency (IBDD), five were isovaleric acidemia (IVA), four were methylmalonic acidemia (MMA), and two were propionic academia (PA). All but one of the patients with MBAD had elevated isovalerylcarnitine levels and corresponding ratios during screening. All patients with GA-1 had elevated glutarylcarnitine levels and corresponding ratios during screening, except for one with a low free carnitine level. The remaining patients presented with elevated acylcarnitine levels during screening and recall. Several variant hotspots were identified in the ACADSB, MCCC1, MCCC2, GCDH, ACAD8, and IVD. The overall incidence of OADs in the study population was 1/10,055 newborns, with MBAD, 3-MCCD, and GA-1 being the three most common. The acylcarnitine profiles and genetic features of most OADs have been elucidated. Our findings provide useful information for newborn screening, genetic diagnosis, and the prevention of OADs.

Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive disorder caused by biallelic variants in the ACAD8 gene, which disrupts valine metabolism. In this study, we report seven individuals identified through newborn screening (NBS) with elevated C4-acylcarnitine levels, including five confirmed patients and two heterozygous carriers. Genetic analysis identified 12 distinct ACAD8 variants, seven of which were novel (c.221C>T, c.518T>C, c.727A>G, c.868G>A, c.947A>T, c.966G>A, c.1058T>C). According to ACMG classification criteria, c.221C>T was classified as likely pathogenic, while the remaining variants were categorized as variants of uncertain significance (VUS). During a mean follow-up of 4.81 years, all patients maintained normal growth patterns but two patients developed neurological symptoms that included recurrent febrile seizures and sensory integration dysfunction. These findings expand the ACAD8 variant spectrum, highlight the phenotypic variability of IBDD, and underscore the importance of long-term follow-up and individualized management strategies.

Isobutyryl-CoA dehydrogenase deficiency is a rare, autosomal recessive hereditary disease caused by a disorder in valine metabolism due to the deficiency of isobutyryl-CoA dehydrogenase. We provided two new mutations for ACAD8 and analyzed new sight to explore the association between the clinical phenotype and genotype of this disease. The concentration of butyrylcarnitine was tested by tandem mass spectrometry. Butyryl carnitine and isobutyryl glycine levels were determined based on urine organic acid analysis. Gene mutations were analyzed through gene sequencing. Five individuals were diagnosed with isobutyryl-CoA dehydrogenase deficiency via newborn screening, and new mutations of ACAD8 encoding isobutyryl-CoA dehydrogenase were found. The mutations were c.1166G>A in exon 10 and c.986C>T in exon 9, which were analyzed as pathogenic sites. Both manifested as an increase in butyrylcarnitine and slightly elevated isobutyryl glycine levels. No abnormalities in growth and development were observed during follow-up. Additionally, we summarized 32 types of ACAD8 mutations reported worldwide, analyzed the distribution of mutations with clinical symptoms, and found them to be mainly concentrated in the N-terminal domain and C-terminal domain. These findings may provide new clues for the clinical diagnosis and management of isobutyryl-CoA dehydrogenase deficiency. In this study, we reported new mutations of ACAD8 and performed a retrospective analysis of isobutyryl CoA dehydrogenase deficiency worldwide. Isobutyryl CoA dehydrogenase deficiency may pose a disease risk during the growth process, thereby requiring long-term follow-up.