Diagnoses of newborns and mothers with carnitine uptake defects through newborn screening

Epidemiology and distribution of 207 rare diseases in China: A systematic literature review

Epidemiological data on rare diseases in China are currently limited. The objective of this study was to provide a comprehensive understanding of the prevalence and incidence of rare diseases by systematically analyzing the available epidemiological data. We conducted a comprehensive search of English and Chinese databases, the Incidence and Prevalence Database, the Chinese Rare Disease Guideline, and the Taiwan Health Promotion Administration from 2010 to 2023. We identified the top diseases and regions based on epidemiological data and present the maximum, minimum, and median prevalence and incidence values in tables and forest plots. 1,264 prevalence and incidence data were retrieved from 277 studies, guidelines and official websites, covering 110 rare diseases (53.1%) and 32 regions (94.1%). In terms of geographical regions, incidence or prevalence data were available for 32 regions (94.1%), excluding Tibet Hui Autonomous Region and Macao Special Administrative Region. In terms of rate, 60 and 77 out of 207 diseases (29.0% and 37.2%) had available incidence and prevalence data, respectively. Eight diseases had an incidence rate equal to or greater than that of 1,000 patients per million. The present study provides a comprehensive epidemiological analysis and valuable insights into the prevalence and incidence of rare diseases in China. Our findings underscore the pressing need for sustained drug research and medical support for individuals and families impacted by rare diseases.

Comparative analysis of inherited metabolic diseases in normal newborns and high-risk children: Insights from a 10-year study in Shanghai

BACKGROUND

Compare the differences between normal newborns and high-risk children with inherited metabolic diseases. The disease profile includes amino acidemias, fatty acid oxidation disorders, and organic acidemias.

METHODS

Data was collected on newborns and children from high-risk populations in Shanghai from December 2010 to December 2020.

RESULTS

232,561 newborns were screened for disorders of organic, amino acid, and fatty acid metabolism. The initial positive rate was 0.66 % (1,526/232,561) and the positive recall rate was 77.85 %. The positive predictive value is 4.71 %. Among them, 56 cases were diagnosed as metabolic abnormalities. The total incidence rate is 1:4153. Hyperphenylalaninemia and short-chain acyl-CoA dehydrogenase are the most common diseases in newborns. In addition, in 56 children, 39 (69.42 %) were diagnosed by genetic sequencing. Some hotspot mutations in 14 IEMs have been observed, including PAH gene c.728G > A, c.611A > G, and ACADS gene c. 1031A > G, c.164C > T. A total of 49,860 symptomatic patients were screened, of which 185 were diagnosed with IEM, with a detection rate of 0.37 %. The most commonly diagnosed diseases in high-risk infants aremethylmalonic acidemia and hyperphenylalaninemia.

CONCLUSION

There are more clinical cases of congenital metabolic errors diagnosed by tandem mass spectrometry than newborn screening. The spectrum of diseases, prevalence, and genetic characteristics of normal newborns and high-risk children are quite different.

Inflammation and Organic Cation Transporters Novel (OCTNs)

Inflammation is a physiological condition characterized by a complex interplay between different cells handled by metabolites and specific inflammatory-related molecules. In some pathological situations, inflammation persists underlying and worsening the pathological state. Over the years, two membrane transporters namely OCTN1 (SLC22A4) and OCTN2 (SLC22A5) have been shown to play specific roles in inflammation. These transporters form the OCTN subfamily within the larger SLC22 family. The link between these proteins and inflammation has been proposed based on their link to some chronic inflammatory diseases such as asthma, Crohn's disease (CD), and rheumatoid arthritis (RA). Moreover, the two transporters show the ability to mediate the transport of several compounds including carnitine, carnitine derivatives, acetylcholine, ergothioneine, and gut microbiota by-products, which have been specifically associated with inflammation for their anti- or proinflammatory action. Therefore, the absorption and distribution of these molecules rely on the presence of OCTN1 and OCTN2, whose expression is modulated by inflammatory cytokines and transcription factors typically activated by inflammation. In the present review, we wish to provide a state of the art on OCTN1 and OCTN2 transport function and regulation in relationships with inflammation and inflammatory diseases focusing on the metabolic signature collected in different body districts and gene polymorphisms related to inflammatory diseases.

Genetic Susceptibility to Arrhythmia Phenotypes in a Middle Eastern Cohort of 14,259 Whole-Genome Sequenced Individuals

Background: The current study explores the genetic underpinnings of cardiac arrhythmia phenotypes within Middle Eastern populations, which are under-represented in genomic medicine research. Methods: Whole-genome sequencing data from 14,259 individuals from the Qatar Biobank were used and contained 47.8% of Arab ancestry, 18.4% of South Asian ancestry, and 4.6% of African ancestry. The frequency of rare functional variants within a set of 410 candidate genes for cardiac arrhythmias was assessed. Polygenic risk score (PRS) performance for atrial fibrillation (AF) prediction was evaluated. Results: This study identified 1196 rare functional variants, including 162 previously linked to arrhythmia phenotypes, with varying frequencies across Arab, South Asian, and African ancestries. Of these, 137 variants met the pathogenic or likely pathogenic (P/LP) criteria according to ACMG guidelines. Of these, 91 were in ACMG actionable genes and were present in 1030 individuals (~7%). Ten P/LP variants showed significant associations with atrial fibrillation p < 2.4 × 10-10. Five out of ten existing PRSs were significantly associated with AF (e.g., PGS000727, p = 0.03, OR = 1.43 [1.03, 1.97]). Conclusions: Our study is the largest to study the genetic predisposition to arrhythmia phenotypes in the Middle East using whole-genome sequence data. It underscores the importance of including diverse populations in genomic investigations to elucidate the genetic landscape of cardiac arrhythmias and mitigate health disparities in genomic medicine.

Secondary Carnitine Deficiency in Neonates and Infants Requiring Surgery for Intestinal Obstructions-An Underestimated and Undermanaged Problem

This study aims to elucidate the relationship between intestinal obstruction and carnitine deficiency in neonates and infants. We retrospectively reviewed medical records of 330 neonates and infants, younger than six months, who underwent surgery for intestinal obstruction at our institute from January 2009 to April 2022. The analysis focused on clinical symptoms, related signs, complications, and etiology of the intestinal obstruction. Tandem mass spectrometry (MS/MS) or urine organic acid analysis was conducted for 47 patients, revealing carnitine deficiency in 16 patients. The incidence of carnitine deficiency was 34.0% in the suspicious group and 4.8% overall, significantly higher than in the general population in Taiwan. Notably, patients with carnitine deficiency experienced prolonged ileus, with a mean fasting duration of 41.7 days (range 7.8-65.5 days), compared to 10.8 days (range 8.2-13.4 days) in patients without carnitine deficiency. Carnitine replacement therapy was administered to twelve patients at dosages ranging from 32 to 90 mg/kg/day. One patient exhibited a drug allergy with skin rashes. Our findings suggest that carnitine deficiency should be considered in cases of neonatal and infant intestinal obstruction. Replacement therapy is straightforward and can be prognostically beneficial for some patients. Therefore, we recommend generalizing MS/MS and urine organic acid analysis, particularly for patients with prolonged ileus.

A novel pathogenic variant in the carnitine transporter gene, SLC22A5, in association with metabolic carnitine deficiency and cardiomyopathy features

BACKGROUND

Primary carnitine deficiency (PCD) denotes low carnitine levels with an autosomal recessive pattern of inheritance. Cardiomyopathy is the most common cardiac symptom in patients with PCD, and early diagnosis can prevent complications. Next-generation sequencing can identify genetic variants attributable to PCD efficiently.

OBJECTIVE

We aimed to detect the genetic cause of the early manifestations of hypertrophic cardiomyopathy and metabolic abnormalities in an Iranian family.

METHODS

We herein describe an 8-year-old boy with symptoms of weakness and lethargy diagnosed with PCD through clinical evaluations, lab tests, echocardiography, and cardiac magnetic resonance imaging. The candidate variant was confirmed through whole-exome sequencing, polymerase chain reaction, and direct Sanger sequencing. The binding efficacy of normal and mutant protein-ligand complexes were evaluated via structural modeling and docking studies.

RESULTS

Clinical evaluations, echocardiography, and cardiac magnetic resonance imaging findings revealed hypertrophic cardiomyopathy as a clinical presentation of PCD. Whole-exome sequencing identified a new homozygous variant, SLC22A5 (NM_003060.4), c.821G > A: p.Trp274Ter, associated with carnitine transport. Docking analysis highlighted the impact of the variant on carnitine transport, further indicating its potential role in PCD development.

CONCLUSIONS

The c.821G > A: p.Trp274Ter variant in SLC22A5 potentially acted as a pathogenic factor by reducing the binding affinity of organic carnitine transporter type 2 proteins for carnitine. So, the c.821G > A variant may be associated with carnitine deficiency, metabolic abnormalities, and cardiomyopathic characteristics.

Systemic primary carnitine deficiency induces severe arrhythmia due to shortening of QT interval

BACKGROUND

Systemic primary carnitine deficiency (PCD) is characterized by cardiomyopathy and arrhythmia. Without carnitine supplementation, progression is usually towards fatal cardiac decompensation. While the cardiomyopathy is most likely secondary to energy deficiency, the mechanism of arrhythmia is unclear, and may be related to a short QT interval.

OBJECTIVE

We aim to describe rhythmic manifestations at diagnosis and with carnitine supplementation.

METHODS

French patients diagnosed for PCD were retrospectively included. Clinical and para clinical data at diagnosis and during follow-up were collected. Electrocardiograms with QT interval measurements were blinded reviewed by two paediatric cardiologists.

RESULTS

Nineteen patients (median age at diagnosis 2.3 years (extremes 0.3-28.9)) followed in 8 French centres were included. At diagnosis, 21% of patients (4/19) had arrhythmia (2 ventricular fibrillations, 1 ventricular tachycardia and 1 sudden death), and 84% (16/19) had cardiomyopathy. Six electrocardiograms before treatment out of 11 available displayed a short QT (QTc < 340 ms). Median corrected QTc after carnitine supplementation was 404 ms (extremes 341-447) versus 350 ms (extremes 282-421) before treatment (p < 0.001). The whole QTc was prolonged, and no patient reached the criterion of short QT syndrome with carnitine supplementation. Three patients died, probably from rhythmic cause without carnitine supplementation (two extra-hospital sudden deaths and one non-recoverable rhythmic storm before carnitine supplementation), whereas no rhythmic complication occurred in patients with carnitine supplementation.

CONCLUSION

PCD is associated with shortening of the QT interval inducing severe arrhythmia. A potential explanation would be a toxic effect of accumulated fatty acid and metabolites on ionic channels embedded in the cell membrane. Carnitine supplementation normalizes the QTc and prevents arrhythmia. Newborn screening of primary carnitine deficiency would prevent avoidable deaths.

Newborn screening for primary carnitine deficiency: who will benefit? - a retrospective cohort study

BACKGROUND

Newborn screening (NBS) programmes identify a wide range of disease phenotypes, which raises the question whether early identification and treatment is beneficial for all. This study aims to answer this question for primary carnitine deficiency (PCD) taking into account that NBS for PCD identifies newborns with PCD and also until then undiagnosed mothers.

METHODS

We investigated clinical, genetic (variants in SLC22A5 gene) and functional (carnitine transport activity in fibroblasts) characteristics of all referred individuals through NBS (newborns and mothers) and clinically diagnosed patients with PCD (not through NBS). Disease phenotype in newborns was predicted using data from PCD mothers and cases published in literature with identical SLC22A5 variants.

RESULTS

PCD was confirmed in 19/131 referred newborns, 37/82 referred mothers and 5 clinically diagnosed patients. Severe symptoms were observed in all clinically diagnosed patients, 1 newborn and none of the mothers identified by NBS. PCD was classified as severe in all 5 clinically diagnosed patients, 3/19 newborns and 1/37 mothers; as benign in 8/19 newborns and 36/37 mothers and as unknown in 8/19 newborns. Carnitine transport activity completely separated severe phenotype from benign phenotype (median (range): 4.0% (3.5-5.0)] vs 26% (9.5-42.5), respectively).

CONCLUSION

The majority of mothers and a significant proportion of newborns with PCD identified through NBS are likely to remain asymptomatic without early treatment. Conversely, a small proportion of newborns with predicted severe PCD could greatly benefit from early treatment. Genetic variants and carnitine transport activity can be used to distinguish between these groups.

Collaborative evaluation study on 18 candidate diseases for newborn screening in 1.77 million samples

Analytical and therapeutic innovations led to a continuous but variable extension of newborn screening (NBS) programmes worldwide. Every extension requires a careful evaluation of feasibility, diagnostic (process) quality and possible health benefits to balance benefits and limitations. The aim of this study was to evaluate the suitability of 18 candidate diseases for inclusion in NBS programmes. Utilising tandem mass spectrometry as well as establishing specific diagnostic pathways with second-tier analyses, three German NBS centres designed and conducted an evaluation study for 18 candidate diseases, all of them inherited metabolic diseases. In total, 1 777 264 NBS samples were analysed. Overall, 441 positive NBS results were reported resulting in 68 confirmed diagnoses, 373 false-positive cases and an estimated cumulative prevalence of approximately 1 in 26 000 newborns. The positive predictive value ranged from 0.07 (carnitine transporter defect) to 0.67 (HMG-CoA lyase deficiency). Three individuals were missed and 14 individuals (21%) developed symptoms before the positive NBS results were reported. The majority of tested candidate diseases were found to be suitable for inclusion in NBS programmes, while multiple acyl-CoA dehydrogenase deficiency, isolated methylmalonic acidurias, propionic acidemia and malonyl-CoA decarboxylase deficiency showed some and carnitine transporter defect significant limitations. Evaluation studies are an important tool to assess the potential benefits and limitations of expanding NBS programmes to new diseases.

A Study of Maternal Patients Diagnosed with Inborn Errors of Metabolism Due to Positive Newborn Mass Screening in Their Newborns

BACKGROUND

There are reports of mothers being diagnosed with inborn errors of metabolism (IEM) via positive newborn screening (NBS) of their newborns. Mothers with IEM are often considered to have mild cases of little pathological significance. Based in Niigata Prefecture, this study aimed to investigate mothers newly diagnosed with IEM via positive NBS in their newborns using tandem mass spectrometry, and to clarify the disease frequency and severity.

METHODS

This was a single-institution, population-based, retrospective study. The subjects were mothers whose newborns had false-positive NBS, among 80,410 newborns who underwent NBS between April 2016 and May 2021.

RESULT

there were 3 new mothers were diagnosed with IEM (2 with primary systemic carnitine deficiency (PCD) and 1 with 3-methylcrotonyl-CoA carboxylase deficiency) out of 5 who underwent examination among 18 false positives. The opportunity for diagnosis was low C0 and high C5-OH acylcarnitine levels in their newborn. Two novel SLC22A5 variants (c.1063T > C/c.1266A > G) were identified in patients with PCD. None of the patients had any complications at the time of diagnosis, but two patients showed improvement in fatigue and headache after taking oral carnitine.

CONCLUSION

New mothers with IEM cannot be considered as mild cases and need to be treated when necessary. The two novel SLC22A5 variants further expand the variant spectrum of PCD.

A qualitative study on the perspectives of mothers who had been diagnosed with primary carnitine deficiency through newborn screening of their child

BACKGROUND

Primary carnitine deficiency is an inborn error of metabolism, which can lead to life-threating complications early in life. Low carnitine levels can be detected by newborn bloodspot screening (NBS). However, NBS can also identify, mostly asymptomatic, mothers with primary carnitine deficiency. To identify mothers' needs and areas for improving screening practice, this study explored the experiences with, and opinions on primary carnitine deficiency screening in NBS among women diagnosed through NBS of their newborn.

METHODS

Twelve Dutch women were interviewed, 3-11 years after diagnosis. Data were analysed using a thematic approach.

RESULTS

Four main themes were derived: 1) psychological impact of primary carnitine deficiency diagnosis, 2) becoming a patient and "patient-in-waiting", 3) information issues and care provision, and 4) primary carnitine deficiency as part of the NBS panel. Mothers shared that they did not experience major psychological distress of the diagnosis. They did experience (recall) various emotions following the initial abnormal NBS result, including fear and anxiety as well as relief, and emotions regarding their own diagnosis, including uncertainty about health risks and treatment effectiveness. Some felt a patient-in-waiting. Many participants experienced a lack of information, especially shortly after receiving the abnormal NBS result. All shared the belief that screening for primary carnitine deficiency in NBS is beneficial for the newborn, and, given the information they received, also considered the knowledge beneficial for their own health.

CONCLUSIONS

Psychological burden following diagnosis was experienced by women as limited, although the experienced lack of information amplified feelings of uncertainty and anxiety. Most mothers believed that benefits of knowing about primary carnitine deficiency outweighed the disadvantages. Mothers' perspectives should be incorporated in policy-making about primary carnitine deficiency in NBS.

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.

Assessment of carnitine excretion and its ratio to plasma free carnitine as a biomarker for primary carnitine deficiency in newborns

In the Netherlands, newborns are referred by the newborn screening (NBS) Program when a low free carnitine (C0) concentration (<5 μmol/l) is detected in their NBS dried blood spot. This leads to ~85% false positive referrals who all need an invasive, expensive and lengthy evaluation. We investigated whether a ratio of urine C0 / plasma C0 (RatioU:P) can improve the follow-up protocol for primary carnitine deficiency (PCD). A retrospective study was performed in all Dutch metabolic centres, using samples from newborns and mothers referred by NBS due to low C0 concentration. Samples were included when C0 excretion and plasma C0 concentration were sampled on the same day. RatioU:P was calculated as (urine C0 [μmol/mmol creatinine])/(plasma C0 [μmol/l]). Data were available for 59 patients with genetically confirmed PCD and 68 individuals without PCD. The RatioU:P in PCD patients was significantly higher (p value < 0.001) than in those without PCD, median [IQR], respectively: 3.4 [1.2-9.5], 0.4 [0.3-0.8], area under the curve (AUC) 0.837. Classified for age (up to 1 month) and without carnitine suppletion (PCD; N = 12, Non-PCD; N = 40), medians were 6.20 [4.4-8.8] and 0.37 [0.24-0.56], respectively. The AUC for RatioU:P was 0.996 with a cut-off required for 100% sensitivity at 1.7 (yielding one false positive case). RatioU:P accurately discriminates between positive and false positive newborn referrals for PCD by NBS. RatioU:P is less effective as a discriminative tool for PCD in adults and for individuals that receive carnitine suppletion.

Clinical, biochemical, and molecular genetic characteristics of patients with primary carnitine deficiency identified by newborn screening in Shanghai, China

Background: Primary carnitine deficiency (PCD) is an autosomal recessive disease caused by mutations in the SLC22A5 gene, which encodes the organic cation transporter 2 (OCTN2). Patients with PCD may be at risk of skeletal or cardiac myopathy, metabolic decompensation, and even sudden death. This study aimed to analyze the biochemical, clinical, and genetic characteristics of PCD patients identified by newborn screening (NBS) in Shanghai. Methods: Dried blood spot (DBS) samples of newborns were analyzed through tandem mass spectrometry (MS/MS) from January 2003 to December 2021. Newborns with low free carnitine (C0) levels were recalled. Mutation in the SLC22A5 gene was analyzed on suspected positive newborns with low C0 levels after recall. Results: 1,247,274 newborns were screened by MS/MS and 40 newborns were diagnosed with PCD, therefore the incidence of PCD in Shanghai was approximately 1:31,200. The mean C0 level in newborns with PCD was 5.37 ± 1.79 μmol/L before treatment and increased to 24.45 ± 10.87 μmol/L after treatment with L-carnitine. Twenty-three different variants were identified in the SLC22A5 gene, including 8 novel variants, of which c.51C>G (p.F17L) was the most frequent (27.27%, 18/66), followed by c.1400C>G (p.S467C) (25.76%, 17/66). Almost all the screened PCD patients were asymptomatic. Conclusion: NBS via MS/MS was a quick and efficient method for the early diagnosis of PCD. The incidence of PCD in Shanghai was 1:31,200. Eight novel variants were identified, which greatly expanded the variant spectrum of SLC22A5. MS/MS combined with genetic testing could effectively improve the diagnostic accuracy of PCD.

Primary carnitine deficiency is a life-long disease

Primary carnitine deficiency is a rare autosomal recessive disease associated with acute hypoketotic hypoglycaemia, cardiomyopathy and sudden cardiac death. Effective treatment with carnitine supplementation is available. An 18 months old boy, who presented with cardiomyopathy was diagnosed with primary carnitine deficiency, and carnitine supplementation resulted in a full recovery. At age 13 years, he discontinued his medication and at 20 years, he discontinued clinical monitoring. Nine years later, age 29, he presented with heart failure and atrial fibrillation and was admitted to an intensive care unit, where he was treated with furosemide, enoximone and intravenous carnitine supplementation, this lead to improved cardiac function within 2 weeks, and with continued oral carnitine supplements, his left ventricular ejection fraction normalised. The last 8 years were uneventful and he continued to attend his regular follow-up visits at a specialised metabolic outpatient clinic. We report recurrent reversible severe heart failure in a patient with primary carnitine deficiency; it was directly related to non-compliance to carnitine supplementation (and monitoring). This case report emphasises first, the importance of continued monitoring of metabolic disease patients, second, the potential reversibility of cardiomyopathy in an adult patient, and third, the potential risks in the period of transition from the paediatric to adult care. This is an age where young adults desire to be healthy and ignore the need for ongoing medical treatment, even as simple as oral suppletion. Before they reach this age, adequate disease insight and self-management of the disease should be promoted.

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%.

Clinical characteristics of primary carnitine deficiency: A structured review using a case-by-case approach

A broad spectrum of signs and symptoms has been attributed to primary carnitine deficiency (PCD) since its first description in 1973. Advances in diagnostic procedures have improved diagnostic accuracy and the introduction of PCD in newborn screening (NBS) programs has led to the identification of an increasing number of PCD patients, including mothers of screened newborns, who may show a different phenotype compared to clinically diagnosed patients. To elucidate the spectrum of signs and symptoms in PCD patients, we performed a structured literature review. Using a case-by-case approach, clinical characteristics, diagnostic data, and mode of patient identification were recorded. Signs and symptoms were categorized by organ involvement. In total, 166 articles were included, reporting data on 757 individual patients. In almost 20% (N = 136) of the cases, the diagnosis was based solely on low carnitine concentration which we considered an uncertain diagnosis of PCD. The remaining 621 cases had a diagnosis based on genetic and/or functional (ie, carnitine transporter activity) test results. In these 621 cases, cardiac symptoms (predominantly cardiomyopathy) were the most prevalent (23.8%). Neurological (7.1%), hepatic (8.4%), and metabolic (9.2%) symptoms occurred mainly in early childhood. Adult onset of symptoms occurred in 16 of 194 adult patients, of whom 6 (3.1%) patients suffered a severe event without any preceding symptom (five cardiac events and one coma). In conclusion, symptoms in PCD predominantly develop in early childhood. Most newborns and mothers of newborns detected through NBS remain asymptomatic. However, though rarely, severe complications do occur in both groups.

Carnitines as Mitochondrial Modulators of Oocyte and Embryo Bioenergetics

Recently, the importance of bioenergetics in the reproductive process has emerged. For its energetic demand, the oocyte relies on numerous mitochondria, whose activity increases during embryo development under a fine regulation to limit ROS production. Healthy oocyte mitochondria require a balance of pyruvate and fatty acid oxidation. Transport of activated fatty acids into mitochondria requires carnitine. In this regard, the interest in the role of carnitines as mitochondrial modulators in oocyte and embryos is increasing. Carnitine pool includes the un-esterified l-carnitine (LC) and carnitine esters, such as acetyl-l-carnitine (ALC) and propionyl-l-carnitine (PLC). In this review, carnitine medium supplementation for counteracting energetic and redox unbalance during in vitro culture and cryopreservation is reported. Although most studies have focused on LC, there is new evidence that the addition of ALC and/or PLC may boost LC effects. Pathways activated by carnitines include antiapoptotic, antiglycative, antioxidant, and antiinflammatory signaling. Nevertheless, the potential of carnitine to improve energetic metabolism and oocyte and embryo competence remains poorly investigated. The importance of carnitine as a mitochondrial modulator may suggest that this molecule may exert a beneficial role in ovarian disfunctions associated with metabolic and mitochondrial alterations, including PCOS and reproductive aging.

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

Background

Primary carnitine deficiency (PCD) is an autosomal recessive disorder of carnitine transportation that leads to impaired fatty acid oxidation. Large-scale studies on newborn screening (NBS) for PCD are limited. This study aimed to investigate the biochemical and genetic characteristics of patients with PCD detected through NBS.

Results

A total of 548 247 newborns were screened for PCD between January 2014 and June 2021; 1714 newborns with low free carnitine (C0) levels were called back and 49 patients were diagnosed with PCD. The latest incidence rate in Quanzhou, China, was estimated to be 1 in 11 189 newborns. NBS results showed that the 49 patients had varying degrees of decreased C0 levels, whereas seven patients exhibited normal C0 levels during the recall review. All patients harbored biallelic pathogenic variants of the SLC22A5 gene. Nineteen distinct SLC22A5 variants were detected in these 49 patients, and most of the detected variants were clustered in exons 1, 4, and 7. The top eight variants had an allele frequency of 86.73%. The most common variant was c.760C > T (p.R254*) with an allele frequency of 31.63%, followed by c.51C > G (p.F17L) (17.35%) and c.1400C > G (p.S467C) (16.33%). The C0 level of patients with the N/N genotype was significantly lower than that of the M/M group. The C0 levels of patients with genotypes of R254*/R254* and R254*/F17L were far lower than those of patients with the R254*/S467C genotype.

Conclusions

This study presented more than 500,000 NBS data with the latest incidence of 1:11 189 in the Quanzhou area. The SLC22A5 variant spectrum in the selected southern Chinese population has been updated. Patients with null variants were associated with low C0 levels. Combining NBS with genetic testing is critical to improve screening efficiency because patients with PCD may have normal C0 levels during NBS and recall review.

Validation of amplicon-based next generation sequencing panel for second-tier test in newborn screening for inborn errors of metabolism

Objectives

Next generation sequencing (NGS) technology has allowed cost-effective massive parallel DNA sequencing. To evaluate the utility of NGS for newborn screening (NBS) of inborn errors of metabolism (IEM), a custom panel was designed to target 87 disease-related genes. The pilot study was primarily proposed for second-tier testing under the NBSIEM program in Hong Kong.

Methods

The validation of the panel was performed with two reference genomes and an external quality assurance (EQA) sample. Sequencing libraries were synthesized with amplicon-based approach. The libraries were pooled, spiked-in with 2% PhiX DNA as technical control, for 16-plex sequencing runs. Sequenced reads were analyzed using a commercially available pipeline.

Results

The average target region coverage was 208× and the fraction of region with target depth ≥20× was 95.7%, with a sensitivity of 91.2%. There were 85 out of 87 genes with acceptable coverage, and EQA result was satisfactory. The turnaround time from DNA extraction to completion of variant calling and quality control (QC) procedures was 2.5 days.

Conclusions

The NGS approach with the amplicon-based panel has been validated for analytical performance and is suitable for second-tier NBSIEM test.

Tandem Mass Spectrometry Screening for Inborn Errors of Metabolism in Newborns and High-Risk Infants in Southern China: Disease Spectrum and Genetic Characteristics in a Chinese Population

Inborn errors of metabolism (IEMs) often causing progressive and irreversible neurological damage, physical and intellectual development lag or even death, and serious harm to the family and society. The screening of neonatal IEMs by tandem mass spectrometry (MS/MS) is an effective method for early diagnosis and presymptomatic treatment to prevent severe permanent sequelae and death. A total of 111,986 healthy newborns and 7,461 hospitalized high-risk infants were screened for IEMs using MS/MS to understand the characteristics of IEMs and related gene mutations in newborns and high-risk infants in Liuzhou. Positive samples were analyzed by Sanger sequencing or next-generation sequencing. The results showed that the incidence of IEMs in newborns in the Liuzhou area was 1/3,733, and the incidence of IEMs in high-risk infants was 1/393. Primary carnitine deficiency (1/9,332), phenylketonuria (1/18,664), and isovaleric acidemia (1/37,329) ranked the highest in neonates, while citrullinemia type II ranked the highest in high-risk infants (1/1,865). Further, 56 mutations of 17 IEMs-related genes were found in 49 diagnosed children. Among these, HPD c.941T > C, CBS c.1465C > T, ACADS c.337G > A, c.1195C > T, ETFA c.737G > T, MMACHC 1076bp deletion, PCCB c.132-134delGACinsAT, IVD c.548C > T, c.757A > G, GCDH c.1060G > T, and HMGCL c.501C > G were all unreported variants. Some related hotspot mutations were found, including SLC22A5 c.51C > G, PAH c.1223G > A, IVD c.1208A > G, ACADS c.625G > A, and GCDH c.532G > A. These results show that the overall incidence of IEMs in the Liuzhou area is high. Hence, the scope of IEMs screening and publicity and education should be expanded for a clear diagnosis in the early stage of the disease.

Newborn screening for carnitine transporter defect in Bavaria and the long-term follow-up of the identified newborns and mothers: Assessing the benefit and possible harm based on 19 ½ years of experience

Carnitine transporter defect (CTD) is a potentially life-threatening disorder causing acute metabolic decompensation, cardiac arrhythmia, and cardiac and skeletal myopathies. CTD is included in many newborn screening (NBS) programs. The screening parameter free carnitine, however, is influenced by maternal conditions due to placental transfer. This study reviewed the NBS results for CTD as part of a pilot study in Bavaria, Germany, and the long-term follow-up of the identified patients treated in our center between January 1999 and June 2018. Among 1,816,000 Bavarian NBS samples, six newborns were diagnosed with CTD (incidence of 1:302,667; positive predictive value (PPV) of 1.63% from 2008 to 2018). In the 24 newborns presented to our center for confirmatory testing, we detected four newborns and six mothers with CTD, one newborn and three mothers in whom CTD was presumed but not genetically confirmed, and one mother with glutaric aciduria type I. In 11 newborns, no indication for an inborn error of metabolism was found. The newborns and mothers with CTD had no serious cardiac adverse events or relevant muscular symptoms at diagnosis and during treatment for up to 14 years. Three mothers were lost to follow-up. Revealing a lower incidence than expected, our data confirm that NBS for CTD most likely misses newborns with CTD. It rather produces high numbers of false-positives and a low PPV picking up asymptomatic mothers with a diagnosis of uncertain clinical significance. Our data add to the growing evidence that argues against an implementation of CTD in NBS programs.

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Newborn screening (NBS) aims at early detection and treatment of relevant disorders.

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High numbers of false-positives burden the healthy population and health care systems.

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NBS for carnitine transporter defect produces high numbers of false-positives.

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NBS for carnitine transporter defect picks up asymptomatic mothers.

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Selective screening at clinical suspicion more suitable than population screening.

Maternal Primary Carnitine Deficiency and a Novel Solute Carrier Family 22 Member 5 (SLC22A5) Mutation

Primary carnitine deficiency (PCD) is a rare autosomal recessive disorder caused by loss of function mutations in the solute carrier family 22 member 5 (SLC22A5) gene that encodes a high-affinity sodium-ion–dependent organic cation transporter protein (OCTN2). Reduced carnitine transport results in diminished fatty acid oxidation in heart and skeletal muscle and carnitine wasting in urine. We present a case of PCD diagnosed in an adult female after a positive newborn screen (NBS) for PCD that was not confirmed on follow-up testing. The mother was referred for evaluation of persistent fatigue and possible hypothyroidism even though all measurements of thyroid-stimulating hormone were well within the range of 0.4 to 2.5 mIU/L expected for reproductive-age women. She was found to have unequivocally low levels of both total carnitine and carnitine esters, and genetic testing revealed compound heterozygosity for 2 SLC22A5 mutations. One mutation (c.34G>A [p.Gly12Ser]) is a known missense mutation with partial OCTN2 activity, but the other mutation (c.41G>A [p.Trp14Ter]) is previously unreported and results in a premature stop codon and truncated OCTN2. This case illustrates that some maternal inborn errors of metabolism can be identified by NBS and that maternal carnitine levels should be checked after a positive NBS test for PCD.

Carnitine Responsive Migraine Headache Syndrome: Case Report and Review of the Literature

PURPOSE OF REVIEW

To review carnitine's role in migraine and headache, present a case of a patient with intractable chronic migraine refractory to medications but exquisitely responsive to mitochondrial cofactors with a particularly prompt response to L-carnitine supplementation with dose response, and suggest scenarios where L-carnitine could be considered for prophylactic treatment in migraine and intractable headache with migraine features.

RECENT FINDINGS

Multiple treatments modalities are used to treat migraine, including nutraceutical therapies. Mitochondrial supplements are often used to treat migraine, based on controlled trials. One of the nutraceutical therapies used in neurological and non-neurological conditions is L-carnitine. A few studies have examined the effect of carnitine in patients with migraine. We present a case of a patient with chronic migraine-like headaches found to have carnitine deficiency whose headaches greatly improved with carnitine supplementation. This case suggests that secondary carnitine deficiency may cause chronic migraine. Energy deficiency states occur with migraine, and replenishment of energy substrates has demonstrated some improvement in migraine. Recent studies suggest that L-carnitine with other mitochondrial cofactors may be migraine preventives. The exact link between carnitine and migraine is unknown. Perhaps carnitine deficiency should be in the differential for refractory migraine. Supplementation with L-carnitine merits exploration as a nutraceutical treatment of chronic migraine. Our case suggests that there may be a dose-dependent response to L-carnitine.

Increased detection of primary carnitine deficiency through second-tier newborn genetic screening

BACKGROUND

Newborn screening for primary carnitine deficiency (NBS) is commonly implemented worldwide; however, it has poor sensitivity. This study aimed to evaluate the feasibility of improving screening by including a second-tier genetic assay.

RESULTS

An Agena iPLEX assay was developed to identify 17 common SLC22A5 mutations in Chinese populations and was applied in NBS as a second-tier screening. From January 2017 to December 2018, 204,777 newborns were screened for PCD using tandem mass spectrometry. A total of 316 (0.15%) residual NBS-positive specimens with low free carnitine (C0) levels were subjected to this second-tier screening. The screening identified 20 screen-positive newborns who harboured biallelic mutations in theSLC22A5 gene, 99 carriers with one mutation, and 197 screen-negative newborns with no mutations. Among the 99 carriers, four newborns were found to have a second disease-causing SLC22A5mutation by further genetic analysis. Among the 197 screen-negatives were four newborns with persistently low C0 levels, and further genetic analysis revealed that one newborn had two novel SLC22A5 pathogenic variants. In total, 25 newborns were diagnosed with PCD, for a positive predictive value of 7.91% (25/316). Based on these data, we estimate the incidence of PCD in Quanzhou is estimated to be 1:8191.Thirteen distinct SLC22A5 variants were identified, and the most common was c.760C > T, with an allelic frequency of 32% (16/50), followed by c.1400C > G (7/50, 14%), and c.51C > G (7/50, 14%).

CONCLUSION

Data from this study revealed that 24% (6/25) of PCD cases would have been missed by conventional NBS. This high-throughput iPLEX assay is a powerful tool for PCD genotyping. The addition of this second-tier genetic screening to the current NBS program could identify missed PCD cases, thereby increasing PCD detection. However, further studies are needed to optimise the workflow of the new screening algorithm and to evaluate the cost-effectiveness of this screening approach.

Gene spectrum and clinical traits of 10 patients with primary carnitine deficiency

BACKGROUND

Rare studies focused on the tandem mass spectrometry (MS/MS) findings for the primary carnitine deficiency (PCD) in the neonates in China mainland. In this study, we aim to analyze the gene mutation spectrum of PCD in Fujian Province in China mainland.

METHODS

Primary carnitine deficiency (PCD) samples used in this study were selected from 95,453 cases underwent neonatal screening between May 2015 and February 2020. SLC22A5 gene sequencing was performed on the neonates and their parents with C0 level of less than 8.8 μmol/L.

RESULTS

Ten patients (male: 7; female: 3) were finally included in this study. Among these patients, nine were neonates, and one was maternal decline of C0 of less than 8.8 μmol/L. The maternal case showed two types of mutations of SLC22A5 including c.760C>T(p.R254*) and c.1400C>G(p.S467C). The other nine neonates showed compound mutations involving nine types in 18 sites, among which two mutations [i.e., c.37G>T(p.E13*) and c.694A>G(p.T232A)] were novel that had never been reported before. Bioinformatic analysis indicated that c.37G>T(p.E13*) was a pathogenic mutation, while the c.694A>G (p.T232A) was considered to be likely pathogenic.

CONCLUSION

MS/MS screening on PCD contributed to the early diagnosis and screening. In addition, SLC22A5 gene mutation analysis contributed to the PCD screening.

Newborn screening for primary carnitine deficiency in Quanzhou, China

BACKGROUND AND AIMS

Primary carnitine deficiency (PCD) is an autosomal recessive disease caused by functional defects in the carnitine transporter OCTN2 due to mutations in SLC22A5. Here, we aimed to understand the incidence, clinical, biochemical, and molecular features of PCD in Quanzhou, China.

MATERIALS AND METHODS

Newborn screening (NBS) was performed through tandem mass spectrometry (MS/MS) to detect genetic metabolic diseases. Next-generation sequencing was used to detect SLC22A5 mutations in patients with suspected PCD.

RESULTS

From 364,545 newborns screened, 36 were diagnosed with PCD, in addition to five mothers. The incidence of PCD in children in the Quanzhou area was 1:10126. Eighteen SLC22A5 variants were found, with five novel ones. The most prevalent variant in neonatal and maternal patients was c.760C > T (p.R254*). Twenty-five neonatal patients received L-carnitine supplementation; however, one patient discontinued treatment and sudden death occurred. One sibling presented repeated fatigue, hypoglycemia, and coma, but the symptoms disappeared after treatment. Two mothers with PCD claimed to feel weak and easily fatigued.

CONCLUSION

The incidence of PCD is relatively high in the Quanzhou area. Five novel variants were found, broadening the mutation spectrum of SLC22A5. NBS is effective in identifying PCD, and sudden death may be prevented with timely treatment.

Genomic Sequencing for Newborn Screening: Results of the NC NEXUS Project

Newborn screening (NBS) was established as a public health program in the 1960s and is crucial for facilitating detection of certain medical conditions in which early intervention can prevent serious, life-threatening health problems. Genomic sequencing can potentially expand the screening for rare hereditary disorders, but many questions surround its possible use for this purpose. We examined the use of exome sequencing (ES) for NBS in the North Carolina Newborn Exome Sequencing for Universal Screening (NC NEXUS) project, comparing the yield from ES used in a screening versus a diagnostic context. We enrolled healthy newborns and children with metabolic diseases or hearing loss (106 participants total). ES confirmed the participant's underlying diagnosis in 15 out of 17 (88%) children with metabolic disorders and in 5 out of 28 (∼18%) children with hearing loss. We discovered actionable findings in four participants that would not have been detected by standard NBS. A subset of parents was eligible to receive additional information for their child about childhood-onset conditions with low or no clinical actionability, clinically actionable adult-onset conditions, and carrier status for autosomal-recessive conditions. We found pathogenic variants associated with hereditary breast and/or ovarian cancer in two children, a likely pathogenic variant in the gene associated with Lowe syndrome in one child, and an average of 1.8 reportable variants per child for carrier results. These results highlight the benefits and limitations of using genomic sequencing for NBS and the challenges of using such technology in future precision medicine approaches.

Performance of Expanded Newborn Screening in Norway Supported by Post-Analytical Bioinformatics Tools and Rapid Second-Tier DNA Analyses

In 2012, the Norwegian newborn screening program (NBS) was expanded (eNBS) from screening for two diseases to that for 23 diseases (20 inborn errors of metabolism, IEMs) and again in 2018, to include a total of 25 conditions (21 IEMs). Between 1 March 2012 and 29 February 2020, 461,369 newborns were screened for 20 IEMs in addition to phenylketonuria (PKU). Excluding PKU, there were 75 true-positive (TP) (1:6151) and 107 (1:4311) false-positive IEM cases. Twenty-one percent of the TP cases were symptomatic at the time of the NBS results, but in two-thirds, the screening result directed the exact diagnosis. Eighty-two percent of the TP cases had good health outcomes, evaluated in 2020. The yearly positive predictive value was increased from 26% to 54% by the use of the Region 4 Stork post-analytical interpretive tool (R4S)/Collaborative Laboratory Integrated Reports 2.0 (CLIR), second-tier biochemical testing and genetic confirmation using DNA extracted from the original dried blood spots. The incidence of IEMs increased by 46% after eNBS was introduced, predominantly due to the finding of attenuated phenotypes. The next step is defining which newborns would truly benefit from screening at the milder end of the disease spectrum. This will require coordinated international collaboration, including proper case definitions and outcome studies.

Neonatal Screening on Tandem Mass Spectrometry as a Powerful Tool for the Reassessment of the Prevalence of Underestimated Diseases in Newborns and Their Family Members: A Focus on Short Chain Acyl-CoA Dehydrogenase Deficiency

Early detection of disabling diseases, prior to clinical manifestations, is the primary goal of newborn screening (NS). Indeed, the required number of core and secondary conditions selected for screening panels is increasing in many countries. Furthermore, newborn screening can lead to diagnosis of maternal diseases such as vitamin B12 deficiency or 3-MethylcrotonylCoA-carboxylase deficiency (3MCC). NS became mandatory in Sicily in December 2017. Here we report NS data collected between December 2017 and April 2020. Our results show that tandem mass spectrometry is a powerful tool for discovery of underestimated disease in newborns and their family members. Our panel included short chain acyl-CoA dehydrogenase deficiency (SCADD). Here, we report that results of our investigation led to reassessment of SCADD prevalence in our population. The infant and adult patients diagnosed in our study had previously not shown overt symptoms.

The Nutraceutical Value of Carnitine and Its Use in Dietary Supplements

Carnitine can be considered a conditionally essential nutrient for its importance in human physiology. This paper provides an updated picture of the main features of carnitine outlining its interest and possible use. Particular attention has been addressed to its beneficial properties, exploiting carnitine's properties and possible use by considering the main in vitro, in animal, and human studies. Moreover, the main aspects of carnitine-based dietary supplements have been indicated and defined with reference to their possible beneficial health properties.

Screening 3.4 million newborns for primary carnitine deficiency in Zhejiang Province, China

Testing for primary carnitine deficiency (PCD) has been implemented in many newborn screening (NBS) programs, but few large-scale studies on NBS for PCD have been reported in China. This study aimed to assess the incidence and biochemical, clinical, and genetic characteristics of PCD discovered by NBS. Dried blood spots from newborns were analyzed by tandem mass spectrometry (MS/MS) and suspected positive patients were further tested using molecular genetic analysis. Infants who carried two variants in SLC22A5 or those with extremely low free carnitine levels during recall were referred for follow-up and treatment. Over 3.4 million newborns were screened and 113 newborns were diagnosed with PCD, yielding a positive predictive value of 1.93%. In addition, 63 mothers with PCD were identified. The incidence of PCD in newborns and mothers in Zhejiang was 1:30,182 and 1:54,137, respectively. Thirty-seven distinct variants were identified in SLC22A5 of which 10 were novel. c.1400C > G (p.S467C) was the most prevalent variant in both newborns and mothers with PCD, while c.760C > T (p.R254*), which is reportedly common in other Chinese regions, was rarely detected in maternal PCD patients. This study reports the largest series of patients with PCD detected by NBS and identifies 10 novel variants, expanding the variant spectrum of SLC22A5.

Newborn screening and diagnosis of inborn errors of metabolism: A 5-year study in an eastern Chinese population

Inborn errors of metabolism (IEMs) can cause intellectual disability or even death in children. To evaluate the disease spectrum and genetic characteristics of IEMs in Jining City of Shandong Province in East China, we used tandem mass spectrometry (MS/MS) technology for IEMs screening combined with genetic analysis. Newborns were screened from July 14, 2014, to December 31, 2018. Amino acid and carnitine contents were detected by MS/MS. According to the results for normal newborns, the reference range of our laboratory was established with the percentile method. The suspected positive newborns were further diagnosed using next-generation sequencing. A total of 514,234 newborns were screened, and 265 were diagnosed with IEMs, with a detection rate of 1:1941. Of the 265 patients, 130 (49.06%) had organic acid disorders, 83 (31.32%) had amino acid disorders, 34 (12.83%) had fatty acid oxidation disorders, and 18 (6.79%) had urea circulatory disorders. PAHD and MMA were the two most common disorders. IEMs-associated genes were identified in 233 patients. Our data indicated that IEMs are never uncommon in Jining, and the disease spectrum and genetic background were clearly elucidated, contributing to the treatment and prenatal genetic counseling of these disorders in the region.

Molecular investigation in Chinese patients with primary carnitine deficiency

BACKGROUND

Primary carnitine deficiency (PCD) is an autosomal recessive disorder of carnitine transportation caused by mutations in the SLC22A5 that lead to low serum carnitine levels and decreased intracellular carnitine accumulation. Characteristic clinical findings are hypoketotic hypoglycemia and skeletal and cardiac myopathy.

OBJECTIVE

To genetically diagnose 24 unrelated Chinese patients with PCD, including 18 infants and six adults.

METHODS

The entire coding region and the intron-exon boundaries of SLC22A5 were amplified by polymerase chain reaction (PCR). In silico analyses and reverse transcription-polymerase chain reaction (RT-PCR) were used to predict variants' impact on protein structure and function.

RESULTS

Disease-causing variants in the SLC22A5 were identified in all 24 subjects, and c.288delG, c.495C>A, c.774_775insTCG, c.824+1G>A, and c.1418G>T were novel. The novel variant c.824+1G>A caused a truncated protein p.Phe276Tyrfs*8.

CONCLUSIONS

We identified 13 variants in the SLC22A5 in 24 PCD patients, and five of these variants are novel mutations. c.824+1G>A was confirmed to alter mRNA splicing by reverse transcription PCR. Furthermore, our findings broaden the mutation spectrum of SLC22A5 and the understanding of the diverse and variable effects of PCD variants.

Molecular Autopsy Implicates Primary Carnitine Deficiency in Sudden Unexplained Death and Reversible Short QT Syndrome

We report a case of sudden unexplained death in a young asymptomatic woman in whom postmortem genetic testing after a negative autopsy identified a homozygous pathogenic mutation in SLC22A5 which leads clinically to primary carnitine deficiency (PCD). Her brother was subsequently diagnosed clinically with short QT syndrome, received an implantable defibrillator, and was then found to carry the same pathogenic homozygous mutation and critically low levels of carnitine. His QT interval improved with the use of carnitine supplementation, highlighting the close relationship between electrophysiology and biochemistry, and the importance of postmortem genetic testing in the clinical management of surviving relatives.

A newborn with seizures born to a mother diagnosed with primary carnitine deficiency

BACKGROUND

Maternofetal carnitine transport through the placenta is the main route of fetal carnitine uptake. Decreased free carnitine levels discovered by newborn screening has identified many asymptomatic adult women with systemic primary carnitine deficiency (PCD). Here, we presented amplitude integrated electroencephalogram (aEEG) and magnetic resonance imaging (MRI) findings from a neonate with epilepsy whose mother was carnitine deficient.

CASE PRESENTATION

A one-day-old female newborn was admitted after experiencing seizures for half a day; status epilepticus was found on the continuous normal voltage background pattern with immature sleep-wake cycling during aEEG monitoring. On T1-weighted, T2-weighted, FLAIR, and DWI head MRI, there were various degrees of hyperintense signals and diffusion restrictions in the deep white matter of the right hemisphere. Tandem mass spectrometry discovered carnitine deficiency on the second day, which elevated to normal by the 9th day before L-carnitine supplementation was started. The patient was treated with phenobarbital after admission. No further seizures were noted by day 5. It was confirmed that the patient's mother had a low level of serum-free carnitine. Gene analyses revealed that the newborn had heterozygote mutations on c.1400C > G of the SLC22A5 gene, and her mother had homozygous mutations on c.1400C > G. The patient had a good outcome at the 8-month follow up.

CONCLUSIONS

Maternal carnitine deficiency that occurs during the perinatal period may manifest as secondary epilepsy with cerebral injury in neonates. The short-term neurodevelopmental outcomes were good. Early diagnosis of asymptomatic PCD in female patients can provide guidance for future pregnancies.

Genomic Sequencing Expansion and Incomplete Penetrance

BACKGROUND

Genetic data have the potential to impact patient care significantly. In primary care and in the ICU, patients are undergoing genetic testing. Genetics is also transforming cancer care and undiagnosed diseases. Optimal personalized medicine relies on the understanding of disease penetrance. In this article, I examine the complexity of penetrance.

METHODS

In this article, I assess how variable penetrance can be seen with many diseases, including those of different modes of inheritance, and how genomic testing is being applied effectively for many diseases. In this article, I also identify challenges in the field, including the interpretation of gene variants.

RESULTS

Using advancing bioinformatics and detailed phenotypic assessment, we can increase the yield of genomic testing, particularly for highly penetrant conditions. The technologies are useful and applicable to different medical situations.

CONCLUSIONS

There are now effective genome diagnostics for many diseases. However, the best personalized application of these data still requires skilled interpretation.

The decision to discontinue screening for carnitine uptake disorder in New Zealand

When screening for carnitine uptake disorder (CUD), the New Zealand (NZ) newborn screening (NBS) service identified infants as screen-positive if they had initial and repeat free carnitine (C0) levels of less than 5.0 μmol/L. Since 2006, the NBS service has identified two infants with biochemical and genetic features consistent with neonatal CUD and nine mothers with features consistent with maternal CUD. A review of the literature suggests that these nine women reflect less than half the true prevalence and that CUD is relatively common. However, the NZ results (two infants) suggest a very low sensitivity and positive predictive value of NBS. While patients presenting with significant disease due to CUD are well described, the majority of adults with CUD are asymptomatic. Nonetheless, treatment with high-dose oral L-carnitine is recommended. Compliance with oral L-carnitine is likely to be poor long term. This may represent a specific risk as treatment could repress the usual compensatory mechanisms seen in CUD, such that a sudden discontinuation of treatment may be dangerous. L-carnitine is metabolized to trimethylamine-N-oxide (TMAO) and treated patients have extremely high plasma TMAO levels. TMAO is an independent risk factor for atherosclerosis and, thus, caution should be exercised regarding long-term treatment with high-dose carnitine of asymptomatic patients who may have a biochemical profile without disease. Due to these concerns, the NZ Newborn Metabolic Screening Programme (NMSP) initiated a review via a series of advisory and governance committees and decided to discontinue screening for CUD.

[Genetic diagnosis of 10 neonates with primary carnitine deficiency]

OBJECTIVE

To study the gene mutation profile of primary carnitine deficiency (PCD) in neonates, and to provide a theoretical basis for early diagnosis and treatment, genetic counseling, and prenatal diagnosis of PCD.

METHODS

Acylcarnitine profile analysis was performed by tandem mass spectrometry using 34 167 dry blood spots on filter paper. The SLC22A5 gene was sequenced and analyzed in neonates with free carnitine (C0) levels lower than 10 μmol/L as well as their parents.

RESULTS

In the acylcarnitine profile analysis, a C0 level lower than 10 μmol/L was found in 10 neonates, but C0 level was not reduced in their mothers. The 10 neonates had 10 types of mutations at 20 different sites in the SLC22A5 gene, which included 4 previously unreported mutations: c.976C>T, c.919delG, c.517delC, and c.338G>A. Bioinformatics analysis showed that the four new mutations were associated with a risk of high pathogenicity.

CONCLUSIONS

Tandem mass spectrometry combined with SLC22A5 gene sequencing may be useful for the early diagnosis of PCD. Identification of new mutations enriches the SLC22A5 gene mutation profile.

Biochemical characteristics of newborns with carnitine transporter defect identified by newborn screening in California

Carnitine transporter defect (CTD; also known as systemic primary carnitine deficiency; MIM 212140) is due to mutations in the SLC22A5 gene and leads to extremely low carnitine levels in blood and tissues. Affected individuals may develop early onset cardiomyopathy, weakness, or encephalopathy, which may be serious or even fatal. The disorder can be suggested by newborn screening. However, markedly low newborn carnitine levels can also be caused by conditions unrelated to CTD, such as the low carnitine levels often associated with normal pregnancies and some metabolic disorders occurring in the mother. In order to clarify the biochemical characteristics most useful for identification of CTD in newborns, we examined California Department of Public Health newborn screening data for CTD from 2005 to 12 and performed detailed chart reviews at six metabolic centers in California. The reviews covered 14 cases of newborn CTD, 14 cases of maternal disorders (CTD, 6 cases; glutaric aciduria, type 1, 5; medium-chain acyl CoA dehydrogenase deficiency, 2; and cobalamin C deficiency, 1), and 154 false-positive cases identified by newborn screening. Our results show that newborns with CTD identified by NBS exhibit different biochemical characteristics, compared to individuals ascertained clinically. Newborns with CTD may have NBS dried blood spot free carnitine near the lower cutoff and confirmatory plasma total and free carnitine levels near the normal lower limit, particularly if obtained within two weeks after birth. These findings raise the concern that true cases of CTD may exist that could have been missed by newborn screening. CTD should be considered as a possible diagnosis in cases with suggestive clinical features, even if CTD was thought to be excluded in the newborn period. Maternal plasma total carnitine and newborn urine total carnitine values are the most important predictors of true CTD in newborns. However, biochemical testing alone does not yield a discriminant rule to distinguish true CTD from low carnitine in newborns due to other causes. Because of this biochemical variability and overlap, molecular genetic testing is imperative to confirm CTD in newborns. Additionally, functional testing of fibroblast carnitine uptake remains necessary for cases in which other confirmatory testing is inconclusive. Even with utilization of all available diagnostic testing methods, confirmation of CTD ascertained by NBS remains lengthy and challenging. Incorporation of molecular analysis as a second tier step in NBS for CTD may be beneficial and should be investigated.

Functional and molecular studies in primary carnitine deficiency

Primary carnitine deficiency is caused by a defect in the OCTN2 carnitine transporter encoded by the SLC22A5 gene. It can cause hypoketotic hypoglycemia or cardiomyopathy in children, and sudden death in children and adults. Fibroblasts from affected patients have reduced carnitine transport. We evaluated carnitine transport in fibroblasts from 358 subjects referred for possible carnitine deficiency. Carnitine transport was reduced to 20% or less of normal in fibroblasts of 140 out of 358 subjects. Sequencing of the 10 exons and flanking regions of the SLC22A5 gene in 95 out of 140 subjects identified causative variants in 84% of the alleles. The missense variants identified in our patients and others previously reported (n = 92) were expressed in CHO cells. Carnitine transport was impaired by 73 out of 92 variants expressed. Prediction algorithms (Polyphen-2, SIFT) correctly predicted the functional effects of expressed variants in about 80% of cases. These results indicate that mutations in the coding region of the SLC22A5 gene cannot be identified in about 16% of the alleles causing primary carnitine deficiency. Prediction algorithms failed to determine the functional effects of amino acid substitutions in this transmembrane protein in about 20% of cases. Therefore, functional studies in fibroblasts remain the best strategy to confirm or exclude a diagnosis of primary carnitine deficiency.

Brain carnitine deficiency causes nonsyndromic autism with an extreme male bias: A hypothesis

Could 10-20% of autism be prevented? We hypothesize that nonsyndromic or "essential" autism involves extreme male bias in infants who are genetically normal, but they develop deficiency of carnitine and perhaps other nutrients in the brain causing autism that may be amenable to early reversal and prevention. That brain carnitine deficiency might cause autism is suggested by reports of severe carnitine deficiency in autism and by evidence that TMLHE deficiency - a defect in carnitine biosynthesis - is a risk factor for autism. A gene on the X chromosome (SLC6A14) likely escapes random X-inactivation (a mixed epigenetic and genetic regulation) and could limit carnitine transport across the blood-brain barrier in boys compared to girls. A mixed, common gene variant-environment hypothesis is proposed with diet, minor illnesses, microbiome, and drugs as possible risk modifiers. The hypothesis can be tested using animal models and by a trial of carnitine supplementation in siblings of probands. Perhaps the lack of any Recommended Dietary Allowance for carnitine in infants should be reviewed. Also see the video abstract here: https://youtu.be/BuRH_jSjX5Y.

Exome sequencing identifies primary carnitine deficiency in a family with cardiomyopathy and sudden death

Pediatric cardiomyopathy is a rare but severe disease with high morbidity and mortality. The causes are poorly understood and can only be established in one-third of cases. Recent advances in genetic technologies, specifically next-generation sequencing, now allow for the detection of genetic causes of cardiomyopathy in a systematic and unbiased manner. This is particularly important given the large clinical variability among pediatric cardiomyopathy patients and the large number of genes (>100) implicated in the disorder. We report on the performance of whole-exome sequencing in members of a consanguineous family with a history of pediatric hypertrophic cardiomyopathy and sudden cardiac death, which led to the identification of a homozygous stop variant in the SLC22A5 gene, implicated in primary carnitine deficiency, as the likely genetic cause. Targeted carnitine tandem mass spectrometry analysis in the patient revealed complete absence of plasma-free carnitine and only trace levels of total carnitine, further supporting the causality of the SLC22A5 variant. l-carnitine supplementation in the proband led to a rapid and marked clinical improvement. This case illustrates the use of exome sequencing as a systematic and unbiased diagnostic tool in pediatric cardiomyopathy, providing an efficient route to the identification of the underlying cause, which lead to appropriate treatment and prevention of premature death.

Primary Carnitine Deficiency - A Rare Treatable Cause of Cardiomyopathy and Massive Hepatomegaly

Systemic primary carnitine deficiency (CDSP) is a rare autosomal recessive disorder caused by a defect in plasma membrane uptake of carnitine due to SLC22A5 gene mutations. A nine-mo-old boy presented with hypertrophic cardiomyopathy, massive hepatomegaly and jaundice. Metabolic testing revealed very low free carnitine levels. Genetic analysis using Sanger sequencing method revealed compound heterozygous mutations in SLC22A5 gene, c. 1354 G > A (p. Glu452Lys, previously reported) and c.231_234del (novel frame-shift). Oral carnitine supplementation resulted in improved clinical outcome with ejection fraction to 75 % and normalization of liver size and enzymes after 3 mo.

Neonatal Screening for Inherited Metabolic Diseases in 2016

The scope of newborn screening (NBS) programs is continuously expanding. NBS programs are secondary prevention interventions widely recognized internationally in the "field of Public Health." These interventions are aimed at early detection of asymptomatic children affected by certain diseases, with the objective to establish a definitive diagnosis and apply the proper treatment to prevent further complications and sequelae and ensure a better quality of life. The most significant event in the history of neonatal screening was the discovery of phenylketonuria in 1934. This disease has been the paradigm of inherited metabolic diseases. The next paradigm was the introduction of tandem mass spectrometry in the NBS programs that make possible the simultaneous measurement of several metabolites and consequently, the detection of several diseases in one blood spot and in an unique analysis. We aim to review the current situation of neonatal screening in 2016 worldwide and show scientific evidence of the benefits for some diseases. We will also discuss future challenges. It should be taken into account that any consideration to expand an NBS panel should involve a rigorous process of decision-making that balances benefits against the risks of harm.

Carnitine transport and fatty acid oxidation

Carnitine is essential for the transfer of long-chain fatty acids across the inner mitochondrial membrane for subsequent β-oxidation. It can be synthesized by the body or assumed with the diet from meat and dairy products. Defects in carnitine biosynthesis do not routinely result in low plasma carnitine levels. Carnitine is accumulated by the cells and retained by kidneys using OCTN2, a high affinity organic cation transporter specific for carnitine. Defects in the OCTN2 carnitine transporter results in autosomal recessive primary carnitine deficiency characterized by decreased intracellular carnitine accumulation, increased losses of carnitine in the urine, and low serum carnitine levels. Patients can present early in life with hypoketotic hypoglycemia and hepatic encephalopathy, or later in life with skeletal and cardiac myopathy or sudden death from cardiac arrhythmia, usually triggered by fasting or catabolic state. This disease responds to oral carnitine that, in pharmacological doses, enters cells using the amino acid transporter B(0,+). Primary carnitine deficiency can be suspected from the clinical presentation or identified by low levels of free carnitine (C0) in the newborn screening. Some adult patients have been diagnosed following the birth of an unaffected child with very low carnitine levels in the newborn screening. The diagnosis is confirmed by measuring low carnitine uptake in the patients' fibroblasts or by DNA sequencing of the SLC22A5 gene encoding the OCTN2 carnitine transporter. Some mutations are specific for certain ethnic backgrounds, but the majority are private and identified only in individual families. Although the genotype usually does not correlate with metabolic or cardiac involvement in primary carnitine deficiency, patients presenting as adults tend to have at least one missense mutation retaining residual activity. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Disorders of carnitine biosynthesis and transport

Carnitine is a hydrophilic quaternary amine that plays a number of essential roles in metabolism with the main function being the transport of long-chain fatty acids from the cytosol to the mitochondrial matrix for β-oxidation. Carnitine can be endogenously synthesized. However, only a small fraction of carnitine is obtained endogenously while the majority is obtained from diet, mainly animal products. Carnitine is not metabolized and is excreted in urine. Carnitine homeostasis is regulated by efficient renal reabsorption that maintains carnitine levels within the normal range despite variabilities in dietary intake. Diseases occurring due to primary defects in carnitine metabolism and homeostasis are comprised in two groups: disorders of carnitine biosynthesis and carnitine transport defect. While the hallmark of carnitine transport defect is profound carnitine depletion, disorders of carnitine biosynthesis do not cause carnitine deficiency due to the fact that both carnitine obtained from diet and efficient renal carnitine reabsorption can maintain normal carnitine levels with the absence of endogenously synthesized carnitine. Carnitine transport defect phenotype encompasses a broad clinical spectrum including metabolic decompensation in infancy, cardiomyopathy in childhood, fatigability in adulthood, or absence of symptoms. The phenotypes associated with the carnitine transport defect result from the unavailability of enough carnitine to perform its functions particularly in fatty acid β-oxidation. Carnitine biosynthetic defects have been recently described and the phenotypic consequences of these defects are still emerging. Although these defects do not result in carnitine deficiency, they still could be associated with pathological phenotypes due to excess or deficiency of intermediate metabolites in the carnitine biosynthetic pathway and potential carnitine deficiency in early stages of life when brain and other organs develop. In addition to these two groups of primary carnitine defects, several metabolic diseases and medical conditions can result in excessive carnitine loss leading to a secondary carnitine deficiency.

The Frequencies of Different Inborn Errors of Metabolism in Adult Metabolic Centres: Report from the SSIEM Adult Metabolic Physicians Group

BACKGROUND

There are few centres which specialise in the care of adults with inborn errors of metabolism (IEM). To anticipate facilities and staffing needed at these centres, it is of interest to know the distribution of the different disorders.

METHODS

A survey was distributed through the list-serve of the SSIEM Adult Metabolic Physicians group asking clinicians for number of patients with confirmed diagnoses, types of diagnoses and age at diagnosis.

RESULTS

Twenty-four adult centres responded to our survey with information on 6,692 patients. Of those 6,692 patients, 510 were excluded for diagnoses not within the IEM spectrum (e.g. bone dysplasias, hemochromatosis) or for age less than 16 years, leaving 6,182 patients for final analysis. The most common diseases followed by the adult centres were phenylketonuria (20.6%), mitochondrial disorders (14%) and lysosomal storage disorders (Fabry disease (8.8%), Gaucher disease (4.2%)). Amongst the disorders that can present with acute metabolic decompensation, the urea cycle disorders, specifically ornithine transcarbamylase deficiency, were most common (2.2%), followed by glycogen storage disease type I (1.5%) and maple syrup urine disease (1.1%). Patients were frequently diagnosed as adults, particularly those with mitochondrial disease and lysosomal storage disorders.

CONCLUSIONS

A wide spectrum of IEM are followed at adult centres. Specific knowledge of these disorders is needed to provide optimal care including up-to-date knowledge of treatments and ability to manage acute decompensation.

Carnitine deficiency induces a short QT syndrome

BACKGROUND

Short QT syndrome is associated with an increased risk of cardiac arrhythmias and unexpected sudden death. Until now, only mutations in genes encoding the cardiac potassium and calcium channels have been implicated in early T-wave repolarization.

OBJECTIVE

The purpose of this study was to confirm a relationship between a short QT syndrome and carnitine deficiency.

METHODS

We report 3 patients affected by primary systemic carnitine deficiency and an associated short QT syndrome. Ventricular fibrillation during early adulthood was the initial symptom in 1 case. To confirm the relationship between carnitine, short QT syndrome, and arrhythmias, we used a mouse model of carnitine deficiency induced by long-term subcutaneous perfusion of MET88.

RESULTS

MET88-treated mice developed cardiac hypertrophy associated with a remodeling of the mitochondrial network. The continuous monitoring of electrocardiograms confirmed a shortening of the QT interval, which was negatively correlated with the plasma carnitine concentration. As in humans, such alterations coincided with the genesis of ventricular premature beats and ventricular tachycardia and fibrillation.

CONCLUSION

Altogether, these results suggest that long-chain fatty acid metabolism influence the morphology and the electrical function of the heart.