Biochemical and genetic characteristics of patients with primary carnitine deficiency identified through newborn screening

Screening primary carnitine deficiency in 10 million Chinese newborns: a systematic review and meta-analysis

BACKGROUND

Primary carnitine deficiency (PCD) is a rare autosomal recessive fatty acid oxidation disorder caused by variants in SLC22A5, with its prevalence and SLC22A5 gene mutation spectrum varying across races and regions. This study aimed to systematically analyze the incidence of PCD in China and delineate regional differences in the prevalence of PCD and SLC22A5 gene variants.

METHODS

PubMed, Embase, Web of Science, and Chinese databases were searched up to November 2023. Following quality assessment and data extraction, a meta-analysis was performed on screening results for PCD among Chinese newborns.

RESULTS

After reviewing 1,889 articles, 22 studies involving 9,958,380 newborns and 476 PCD cases were included. Of the 476 patients with PCD, 469 underwent genetic diagnosis, revealing 890 variants of 934 alleles of SLC22A5, among which 107 different variants were detected. The meta-analysis showed that the prevalence of PCD in China was 0.05‰ [95%CI, (0.04‰, 0.06‰)] or 1/20 000 [95%CI, (1/16 667, 1/25 000)]. Subgroup analyses revealed a higher incidence in southern China [0.07‰, 95%CI, (0.05‰, 0.08‰)] than in northern China [0.02‰, 95%CI, (0.02‰, 0.03‰)] (P < 0.001). Furthermore, the result of the meta-analysis showed that the frequency of the variant with c.1400C > G, c.51C > G, c.760C > T, c.338G > A, and c.428C > T were 45% [95%CI, (34%, 59%)], 26% [95%CI, (22%, 31%)], 14% [95%CI, (10%, 20%)], 6% [95%CI, (4%, 8%)], and 5% [95%CI, (4%, 8%)], respectively. Among the subgroup analyses, the variant frequency of c.1400C > G in southern China [39%, 95%CI, (29%, 53%)] was significantly lower than that in northern China [79‰, 95%CI, (47‰, 135‰)] (P < 0.05).

CONCLUSIONS

This study systematically analyzed PCD prevalence and identified common SLC22A5 gene variants in the Chinese population. The findings provide valuable epidemiological insights and guidance for future PCD screening effects in newborns.

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.

Newborn screening for primary carnitine deficiency using a second-tier genetic test

OBJECTIVES

Newborn screening (NBS) for primary carnitine deficiency (PCD) exhibits suboptimal performance. This study proposes a strategy to enhance the efficacy of second-tier genetic screening by adjusting the cutoff value for free carnitine (C0).

METHODS

Between January 2021 and December 2022, we screened 119,898 neonates for inborn metabolic disorders. Neonates with C0 levels below 12 μmol/L were randomly selected for second-tier genetic screening, employing a novel matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) assay.

RESULTS

In total, 2,515 neonates with C0 <12 μmol/L underwent further screening, including 206 neonates with C0 <8.5 μmol/L and 320 neonates with 8.5G, accounting for 25 % (7/28) of allelic frequencies.

CONCLUSIONS

A novel MALDI-TOF MS assay targeting 21 SLC22A5 variants in a Chinese population was successfully established. This assay exhibits a high detection and diagnostic rate, making it suitable for population-based genetic screening. Combined genetic screening is recommended to enhance the efficiency of PCD-NBS.

Screening of 1.17 million newborns for inborn errors of metabolism using tandem mass spectrometry in Shanghai, China: A 19-year report

BACKGROUND

Inborn errors of metabolism (IEMs) frequently result in progressive and irreversible clinical consequences if not be diagnosed or treated timely. The tandem mass spectrometry (MS/MS)-based newborn screening (NBS) facilitates early diagnosis and treatment of IEMs. The aim of this study was to determine the characteristics of IEMs and the successful deployment and application of MS/MS screening over a 19-year time period in Shanghai, China, to inform national NBS policy.

METHODS

The amino acids and acylcarnitines in dried blood spots from 1,176,073 newborns were assessed for IEMs by MS/MS. The diagnosis of IEMs was made through a comprehensive consideration of clinical features, biochemical performance and genetic testing results. The levels of MS/MS testing parameters were compared between various IEM subtypes and genotypes.

RESULTS

A total of 392 newborns were diagnosed with IEMs from January 2003 to June 2022. There were 196 newborns with amino acid disorders (50.00%, 1: 5910), 115 newborns with organic acid disorders (29.59%, 1: 10,139), and 81 newborns with fatty acid oxidation disorders (20.41%; 1:14,701). Phenylalanine hydroxylase deficiency, methylmalonic acidemia and primary carnitine deficiency were the three most common disorders. Some hotspot variations in eight IEM genes (PAH, SLC22A5, MMACHC, MMUT, MAT1A, MCCC2, ACADM, ACAD8), 35 novel variants and some genotype-biochemical phenotype associations were identified.

CONCLUSIONS

A total of 28 types of IEMs were identified, with an overall incidence of 1: 3000 in Shanghai, China. Our study offered clinical guidance for the implementation of MS/MS-based NBS and genetic counseling for IEMs in this city.

Primary carnitine deficiency: Estimation of prevalence in Chinese population and insights into newborn screening

Primary carnitine deficiency (PCD) caused by pathogenic variants in the solute carrier family 22 member 5 (SLC22A5) gene is a rare autosomal recessive disease that results in defective fatty acid oxidation. PCD can be detected through tandem mass spectrometry (MS/MS), but transplacental transport of free carnitine from mothers may cause false negatives or positives during newborn screening (NBS). This study aimed to analyze the genetic characteristics of SLC22A5 and estimate the prevalence of PCD in the Chinese population, providing useful information for NBS and genetic counseling. We manually curated SLC22A5 pathogenic or likely pathogenic (P/LP) variants according to the American College of Medical Genetics and Genomics (ACMG) guidelines and identified 128 P/LP variants. Based on the China Neonatal Genomes Project (CNGP), the estimated PCD prevalence was 1:17,456, which was higher than that in other populations. The genotype-phenotype association analysis showed that patients carrying homozygous c.760C>T and c.844C>T were more likely to present cardiomyopathy, whereas those carrying homozygous c.1400C>G were more likely to be asymptomatic (all p-values < 0.05). We found that there was no significant difference in initial C0 concentrations between patients and carriers, but there was a significant difference in the second-tier screening of C0 concentration between them (p-value < 0.05). We established a cost-effective variant panel containing 10 high-frequency sites and developed a screening algorithm incorporating gene panels with MS/MS, which could rescue one more patient who was undetected from MS/MS. In conclusion, the prevalence of PCD in the Chinese population is relatively high. The combination of conventional NBS with genetic sequencing is suggested for early diagnosis of PCD.

Newborn screening for inborn errors of metabolism in a northern Chinese population

OBJECTIVES

Newborn screening (NBS) for inborn errors of metabolism (IEMs) has been successfully implemented in China. However, the data on the IEM profiles in many regions are lacking. This study aimed to report the incidence, disease spectrum, and genetic profile of IEMs in northern China.

METHODS

A total of 36,590 newborns were screened using tandem mass spectrometry between January 2016 and April 2022. Newborns with positive results were referred for confirmatory testing.

RESULTS

Ten patients were confirmed to have IEMs, with an overall incidence of 1:3,539 in the Rizhao region. Five types of IEMs were detected, including four patients with propionic acidemia (PA), three patients with methylmalonic acidemia (MMA), one of each with citrin deficiency, primary carnitine deficiency, and isobutyryl-CoA dehydrogenase deficiency. PA was the most common IEM, with an unexpectedly high incidence of 1:8,848, followed by MMA, with an incidence rate of 1:11,797. All patients had abnormal screening markers and harbored biallelic variants in their respective causative genes. Two novel PCCB variants (c.505G>A and c.1123_1124insG) were identified in patients with PA. In silico analyses predicted that these two variants were potentially pathogenic.

CONCLUSIONS

This study preliminarily clarified the incidence, disease spectrum, and genetic profile of IEMs in the Rizhao region. PA is the most common IEM and MMA is the second most common in our region. The two novel identified PCCB variants further expand the variant spectrum of PA. More attention should be paid to NBS, early diagnosis, and management of PA and MA.

A retrospective analysis of MS/MS screening for IEM in high-risk areas

Inborn errors of metabolism (IEM) can lead to severe motor and neurological developmental disorders and even disability and death in children due to untimely treatment. In this study, we used tandem mass spectrometry (MS/MS) for primary screening and recall of those with positive primary screening for rescreening. Further diagnosis was based on biochemical tests, imaging and clinical presentation as well as accurate genetic testing using multi-gene panel with high-throughput sequencing of 130 IEM-related genes. The screening population was 16,207 newborns born between July 1, 2019, and December 31, 2021. Based on the results, 8 newborns were diagnosed with IEM, constituting a detection rate of 1:2,026. Phenylketonuria was the most common form of IEM. In addition, seven genes associated with IEM were detected in these eight patients. All eight patients received standardized treatment starting in the neonatal period, and the follow-up results showed good growth and development. Therefore, our study suggests that MS/MS rescreening for IEM pathogenic variants in high-risk areas, combined with a sequencing validation strategy, can be highly effective in the early detection of affected children. This strategy, combined with early intervention, can be effective in preventing neonatal morbidity and improving population quality.

Newborn Screening of Primary Carnitine Deficiency: An Overview of Worldwide Practices and Pitfalls to Define an Algorithm before Expansion of Newborn Screening in France

Primary Carnitine Deficiency (PCD) is a fatty acid oxidation disorder that will be included in the expansion of the French newborn screening (NBS) program at the beginning of 2023. This disease is of high complexity to screen, due to its pathophysiology and wide clinical spectrum. To date, few countries screen newborns for PCD and struggle with high false positive rates. Some have even removed PCD from their screening programs. To understand the risks and pitfalls of implementing PCD to the newborn screening program, we reviewed and analyzed the literature to identify hurdles and benefits from the experiences of countries already screening this inborn error of metabolism. In this study, we therefore, present the main pitfalls encountered and a worldwide overview of current practices in PCD newborn screening. In addition, we address the optimized screening algorithm that has been determined in France for the implementation of this new condition.

Phenotypic and molecular features of Thai patients with primary carnitine deficiency

BACKGROUND

Primary carnitine deficiency (PCD) is screened by expanded newborn screening (NBS) using tandem mass spectrometry (MS/MS) that can detect both affected neonates and mothers. This study aimed to delineate the clinical, biochemical, and molecular findings of Thai PCD patients.

METHODS

Expanded NBS using MS/MS was implemented in Bangkok and 146,757 neonates were screened between 2014 and 2018. PCD was screened by low free carnitine (C0) levels in dried blood spots. Plasma C0 levels and C0 clearance values were measured in neonates and their mothers with positive screening results. Clinically diagnosed cases were described. The coding regions and intron-exon boundaries of the SLC22A5 gene were sequenced in all cases with low plasma C0 levels.

RESULTS

There were 14 cases with confirmed PCD: two clinically diagnosed cases, and 12 cases identified through NBS including five newborns, six mothers, and one older sibling. Thus, the incidence of PCD in neonates was 1:29,351. All affected neonates and mothers were asymptomatic except one mother with dilated cardiomyopathy. SLC22A5 gene sequencing identified biallelic causative variants in all cases, comprising 10 different variants of which four were novel. c.51C > G (p.Phe17Leu) and c.760C > T (p.Arg254Ter) were the most prevalent variants in this study. Cases with significant clinical features tended to have higher C0 clearance values.

CONCLUSIONS

Primary carnitine deficiency is a common inherited metabolic disorder (IMD) in Thailand. Our findings broaden the spectrum of SLC22A5 variants. The future national NBS program will shed more light on PCD and other IMDs in Thailand.

Outcomes of mitochondrial long chain fatty acid oxidation and carnitine defects from a single center metabolic genetics clinic

Background

Mitochondrial long-chain fatty acid oxidation and carnitine metabolism defects are a group of inherited metabolic diseases. We performed a retrospective cohort study to report on the phenotypic and genotypic spectrum of mitochondrial long-chain fatty acid oxidation and carnitine metabolism defects as well as their treatment outcomes.

Methods

All patients with mitochondrial long-chain fatty acid oxidation and carnitine metabolism defects were included. We divided patients into two groups to compare outcomes of those treated symptomatically (SymX) and asymptomatically (AsymX). We reviewed patient charts for clinical features, biochemical investigations, molecular genetic investigations, cardiac assessments, neuroimaging, treatments, and outcomes.

Results

There were 38 patients including VLCAD (n = 5), LCHAD (n = 4), CACT (n = 3), MAD (n = 1), CPT-I (n = 13), CPT-II (n = 3) deficiencies and CTD (n = 9). Fourteen patients were diagnosed symptomatically (SymX), and 24 patients were diagnosed asymptomatically (AsymX). Twenty-eight variants in seven genes were identified in 36 patients (pathogenic/likely pathogenic n = 25; variant of unknown significance n = 3). Four of those variants were novel. All patients with LCHAD deficiency had the common variant (p.Glu474Gln) in HADHA and their phenotype was similar to the patients reported in the literature for this genotype. Only one patient with VLCAD deficiency had the common p.Val283Ala in ACADVL. The different genotypes in the SymX and AsymX groups for VLCAD deficiency presented with similar phenotypes. Eight patients were treated with carnitine supplementation [CTD (n = 6), CPT-II (n = 1), and MAD (n = 1) deficiencies]. Thirteen patients were treated with a long-chain fat restricted diet and MCT supplementation. A statistically significant association was found between rhabdomyolysis, and hypoglycemia in the SymX group compared to the AsymX group. A higher number of hospital admissions, longer duration of hospital admissions and higher CK levels were observed in the SymX group, even though the symptomatic group was only 37% of the study cohort.

Conclusion

Seven different mitochondrial long-chain fatty acid oxidation and carnitine metabolism defects were present in our study cohort. In our clinic, the prevalence of mitochondrial long-chain fatty acid oxidation and carnitine defects was 4.75%.