Newborn screening for isovaleric acidemia in Quanzhou, China

Newborn Screening for Isovaleric Acidemia: Treatment With Pivalate-Generating Antibiotics Contributed to False C5-Carnitine Positivity in a Chinese Population

BACKGROUND

Newborn screening (NBS) for isovaleric acidemia (IVA) is implemented via tandem mass spectrometry (MS/MS), but false-positive results are still common. In addition, NBS for IVA is limited by a lack of suitable biomarkers, especially after the use of pivaloylester-containing antibiotics.

METHODS

We conducted a retrospective cohort study to explore the clinical correlation between antibiotic administration and false-positive results for isovalerylcarnitine (C5).

RESULTS

A total of 509,313 newborns were recruited from the initial NBS study, only one of whom underwent genetic confirmation, conducted between 2015 and 2020. Significant associations between false-positive C5-carnitine screening results and treatment with pivalate-generating antibiotics were identified with retrospective analysis.

CONCLUSIONS

The current results highlight the detrimental effects of false-positive C5-carnitine screening results. Unless the licensing of pivalate-generating antibiotics for use during the neonatal period is reconsidered, a second-tier test for C5 determination will be necessary.

Current Status of Newborn Bloodspot Screening Worldwide 2024: A Comprehensive Review of Recent Activities (2020-2023)

Newborn bloodspot screening (NBS) began in the early 1960s based on the work of Dr. Robert "Bob" Guthrie in Buffalo, NY, USA. His development of a screening test for phenylketonuria on blood absorbed onto a special filter paper and transported to a remote testing laboratory began it all. Expansion of NBS to large numbers of asymptomatic congenital conditions flourishes in many settings while it has not yet been realized in others. The need for NBS as an efficient and effective public health prevention strategy that contributes to lowered morbidity and mortality wherever it is sustained is well known in the medical field but not necessarily by political policy makers. Acknowledging the value of national NBS reports published in 2007, the authors collaborated to create a worldwide NBS update in 2015. In a continuing attempt to review the progress of NBS globally, and to move towards a more harmonized and equitable screening system, we have updated our 2015 report with information available at the beginning of 2024. Reports on sub-Saharan Africa and the Caribbean, missing in 2015, have been included. Tables popular in the previous report have been updated with an eye towards harmonized comparisons. To emphasize areas needing attention globally, we have used regional tables containing similar listings of conditions screened, numbers of screening laboratories, and time at which specimen collection is recommended. Discussions are limited to bloodspot screening.

Analysis of the genotype–phenotype correlation in isovaleric acidaemia: A case report of long-term follow-up of a chinese patient and literature review

Background

Isovaleric acidaemia (IVA), characterized by an acute metabolic crisis and psychomotor delay, is a rare inherited metabolic disease caused by a deficiency in isovaleryl-CoA dehydrogenase (IVD).

Methods

We report the case of a Chinese patient with IVA who was admitted to Tianjin Children's Hospital and followed up for 8 years. Genetic analysis of the patient and his parents was conducted using the whole-exome sequencing and Sanger sequencing. We searched for similar reported cases in the PubMed and Wanfang databases using the term “isovaleric acidaemia,” reviewed the related literature to obtain a summary of the clinical and genetic characteristics, and analyzed the genotype–phenotype correlations.

Results

The patient presented with encephalopathic symptoms, such as vomiting, lethargy, and somnolence. We identified compound heterozygous variants of the IVD gene, including the unreported variant c.224A>G (p.Asn75Ser) and the reported variant c.1195G>C (p.Asp399His). The child was prescribed a low-protein diet supplemented with L-carnitine. During the 8-year follow-up, no metabolic disorder or encephalopathic symptoms recurred. At present, the child is 11 years of age and has normal mental and motor performance. Another 154 cases identified in 25 relevant references were combined with this case, resulting in a sample of 155 patients, including 52 asymptomatic patients, 64 with neonatal onset, and 39 with the chronic intermittent disease with onset from ages of 1 month to 10 years (median age, 2 years). Among articles that reported sex, the male-to-female ratio was 1:1.06. The cardinal symptoms included vomiting, lethargy, “sweaty foot” odor, poor feeding, developmental delay, and epilepsy. The proportion of variants in regions 123–159 and 356–403 of the IVD protein was greater in symptomatic patients than in asymptomatic patients. Conversely, in asymptomatic patients, the proportion of variants in the 282–318 region was greater than in symptomatic patients.

Conclusion

This case report describes an unreported variant c.224A>G (p.Asn75Ser) of the IVD gene, and summarizes previously reported cases. Furthermore, the correlation between the genotype and clinical phenotype of IVA is analyzed to improve the understanding of this disease.

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

Prenatal Diagnosis of Isovaleric Acidemia From Amniotic Fluid Using Genetic and Biochemical Approaches

Background: Isovaleric acidemia (IVA) is an inborn error of leucine metabolism and different approaches have been applied to its prenatal diagnosis. However, systemic application of a biochemical strategy is rare. To evaluate its reliability and validity, we conducted a retrospective study of our experience with metabolite measurement together with genetic analysis in IVA prenatal diagnosis at a single center.

Methods: A total of eight pregnancies whose probands were diagnosed as IVA were referred to our center for prenatal diagnosis. Prenatal data of genetic analysis and metabolite measurement using tandem mass spectrometry (MS/MS) and gas chromatography/mass spectrometry (GC/MS) in amniotic fluid (AF) samples were retrospectively reviewed.

Results: Genetic and biochemical results were both available in these eight at-risk fetuses. Among them, two fetuses had higher levels of isovalerylcarnitine (C5) and C5/acetylcarnitine (C2) in AF compared with normal reference range and, thus, were determined to be affected, both of whom were found to carry compound heterogeneous mutations according to genetic analysis. The remaining six fetuses were determined to be unaffected based on a normal AF metabolite profile, except one showed slightly elevated C5 and they were found to be carriers according to genetic analysis. However, the level of isovalerylglycine (IVG) could not be detected at all in both groups.

Conclusion: The biochemical analysis, as a quick and convenient method, could be an additional reliable option for the prenatal diagnosis of IVA, especially in families with inconclusive genetic results, and can achieve a more precise diagnosis in conjunction with mutation analysis.

A Simple Flow Injection Analysis-Tandem Mass Spectrometry Method to Reduce False Positives of C5-Acylcarnitines Due to Pivaloylcarnitine Using Reference Ions

Flow injection analysis−tandem mass spectrometry (FIA-TMS) has been applied in a first-tier test of newborn screening (NBS). Although isovalerylcarnitine (i-C5), which is a diagnostic indicator of isovaleric acidemia (IVA), is isobaric with pivaloylcarnitine (p-C5), 2-methylbutyrylcarnitine, and n-valerylcarnitine, these isomers cannot be distinguished by the FIA-TMS. There are many reports of false positives derived from p-C5 due to the use of pivalate-conjugated antibiotics. In this study, we developed a new FIA-TMS method to distinguish i-C5 and p-C5. We found that the intensity ratio of product ions for i-C5 and p-C5 was different in a certain range even under the same analytical conditions. The product ions with the most distinct differences in ionic intensity between the isomers and the collision energies that produce them were determined to be m/z 246.2 > 187.1 and −15 V, respectively. In addition to the quantification ion, a reference ion was defined, and the similarity of the i-C5 and p-C5 reference ion ratios (i-C5 score and p-C5 score, respectively) were used to estimate which isomer (i-C5 and p-C5) was responsible for elevated C5 acylcarnitine in dried blood spots (DBSs). As a result of analyses of 11 DBS samples derived from pivalate-conjugated antibiotics and four DBS samples from IVA patients using our method, it was found that our method was able to correctly determine the type of C5-acylcarnitine (i-C5 or p-C5) in the DBS samples. Implementation of this new FIA-TMS method into the current NBS protocol will allow for a reduction in false positives in IVA.

Biochemical and molecular features of Chinese patients with glutaric acidemia type 1 detected through newborn screening

Background

Glutaric acidemia type 1 (GA1) is a treatable disorder affecting cerebral organic acid metabolism caused by a defective glutaryl-CoA dehydrogenase (GCDH) gene. GA1 diagnosis reports following newborn screening (NBS) are scarce in the Chinese population. This study aimed to assess the acylcarnitine profiles and genetic characteristics of patients with GA1 identified through NBS.

Results

From January 2014 to September 2020, 517,484 newborns were screened by tandem mass spectrometry, 102 newborns with elevated glutarylcarnitine (C5DC) levels were called back. Thirteen patients were diagnosed with GA1, including 11 neonatal GA1 and two maternal GA1 patients. The incidence of GA1 in the Quanzhou region was estimated at 1 in 47,044 newborns. The initial NBS results showed that all but one of the patients had moderate to markedly increased C5DC levels. Notably, one neonatal patient with low free carnitine (C0) level suggest primary carnitine deficiency (PCD) but was ultimately diagnosed as GA1. Nine neonatal GA1 patients underwent urinary organic acid analyses: eight had elevated GA and 3HGA levels, and one was reported to be within the normal range. Ten distinct GCDH variants were identified. Eight were previously reported, and two were newly identified. In silico prediction tools and protein modeling analyses suggested that the newly identified variants were potentially pathogenic. The most common variant was c.1244-2 A>C, which had an allelic frequency of 54.55% (12/22), followed by c.1261G>A (p.Ala421Thr) at 9.09% (2/22).

Conclusions

Neonatal GA1 patients with increased C5DC levels can be identified through NBS. Maternal GA1 patients can also be detected using NBS due to the low C0 levels in their infants. Few neonatal GA1 patients may have atypical acylcarnitine profiles that are easy to miss during NBS; therefore, multigene panel testing should be performed in newborns with low C0 levels. This study indicates that the GCDH variant spectra were heterogeneous in this southern Chinese cohort.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01964-5.