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.

Improved sensitivity and specificity for citrin deficiency using selected amino acids and acylcarnitines in the newborn screening

Citrin deficiency is an autosomal recessive disorder caused by a defect of citrin resulting from mutations in the SLC25A13 gene. Intrahepatic cholestasis and various metabolic abnormalities, including hypoglycemia, galactosemia, citrullinemia, and hyperammonemia may be present in neonates or infants in the "neonatal intrahepatic cholestasis caused by citrin deficiency" (NICCD) form of the disease. Because at present, newborn screening (NBS) for citrin deficiency using citrulline levels in dried blood spots (DBS) can only detect some of the patients, we tried to develop a new evaluation system to more reliably detect newborns with citrin deficiency utilizing parameters already in place in present NBS methods. To achieve this goal, we re-analyzed NBS profiles of amino acids and acylcarnitines in 96 NICCD patients, who were diagnosed through selective screening or positive family history. Hereby, we identified the combined evaluation of arginine (Arg), citrulline (Cit), isoleucine+leucine (Ile + Leu), tyrosine (Tyr), free carnitine (C0) / glutarylcarnitine (C5-DC) ratio in DBS as potentially sensitive to diagnose citrin deficiency in pre-symptomatic newborns. In particular, a scoring system using threshold levels for Arg (≥9 μmol/L), Cit (≥ 39 μmol/L), Ile + Leu (≥ 99 μmol/L), Tyr (≥ 96 μmol/L) and C0/C5-DC ratio (≥327) was significantly effective to detect newborns who later developed NICCD, and could thus be implemented in existing NBS programs at no extra analytical costs whenever citrin deficiency is considered to become a novel target disease.

Carnitine supplementation increases serum concentrations of free carnitine and total acylcarnitine in preterm neonates: A retrospective cohort study

OBJECTIVE

Our goal was to determine the efficacy of the American Society for Parenteral and Enteral Nutrition's recommended carnitine dosage of 5 mg/kg/day in maintaining normal serum free carnitine and total acylcarnitine levels in preterm neonates receiving parenteral nutrition (PN).

STUDY DESIGN

A retrospective cohort study was conducted on neonates born <30 weeks gestation and weighing <1250 g, comparing those who received carnitine supplementation to those without supplementation. Free carnitine and total acylcarnitine data were collected from routine newborn screens in the first days of life and on full enetral feeds. Univariate analysis was performed, and those factors that were significantly different between the two groups were adjusted for using mixed effects analysis.

RESULTS

There were 108 supplemented and 45 unsupplemented neonates in the study. At baseline, free carnitine (19.8 ± 3.3 vs 18.9 ± 3.7 µmol/L, P = 0.53) and total acylcarnitine (26.6 ± 5.1 vs 22.5 ± 7.1 µmol/L, P = 0.11) were similar between the two groups. At full enteral feeds, compared with unsupplemented group, supplemented infants had significantly higher free carnitine (27.1 ± 16.4 vs 17.1 ± 8.5 µmol/L, P < 0.001) and total acylcarnitine (30.3 ± 11.5 vs 20.2 ± 10.1 µmol/L, P < 0.001). None of the supplemented neonates developed biochemical carnitine deficiency as compared with 18% in the unsupplemented group (P < 0.001). No difference was observed in time to reach full lipid provision, and there were no differences in the change in the triglyceride levels from baseline to the time on full PN lipid provision (P = 0.39).

CONCLUSION

Preterm neonates routinely supplemented with parenteral carnitine at 5 mg/kg/day demonstrated higher free carnitine and total acylcarnitine levels at full feeds, with none developing biochemical carnitine deficiency.

Thyroid hormones and carnitine in the second trimester negatively affect neonate birth weight: A prospective cohort study

BACKGROUND

Maternal thyroid hormones and carnitine are reported to affect neonate birth weight during the second trimester, which is one of the most important markers for fetal growth and perinatal mortality and morbidity. Nevertheless, the effect of thyroid hormone and carnitine in the second trimester on birth weight has yet to be understood.

METHOD

This was a prospective cohort study with 844 subjects enrolled during the first trimester. Thyroid hormones, free carnitine (C0), neonate birth weight, as well as other related clinical and metabolic data were collected and assessed.

RESULTS

Pre-pregnancy weight and body mass index (BMI) as well as neonate birth weight were significantly different among different free thyroxine (FT4) level groups. Maternal weight gain and neonate birth weight varied significantly when grouped by different thyroid-stimulating hormone (TSH) levels. There was a significantly positive correlation between C0 and TSH (r = 0.31), free triiodothyronine (FT3) (r = 0.37), and FT4 (r = 0.59) (all P < 0.001). In addition, a significantly negative influence was found between birth weight and TSH (r = -0.48, P = 0.028), so as C0 (r = -0.55, P < 0.001) and FT4 (r = -0.64, P < 0.001). Further assessment detected a stronger combined effect of C0 and FT4 (P < 0.001) and of C0 and FT3 (P = 0.022) on birth weight.

CONCLUSION

Maternal C0 and thyroid hormones are of great importance in neonate birth weight, and routine examination of C0 and thyroid hormones during the second trimester has a positive effect on the intervention of birth weight.

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.

Determination of carnitine ester profile in the children with type 1 diabetes: a valuable step towards a better management

Objective: This study is designed to investigate the levels of carnitine and acylcarnitines (ACs) in the children with diabetes type 1 compared to the healthy subjects.Methods: Forty-two type 1 diabetic children and healthy subjects were recruited in the study, respectively. In addition to FBS and Hb A1C, free carnitine and ACs in butyl-ester form in the fasting blood samples were assessed by isotope dilution mass spectrometry for all diabetics and controls using the tandem mass spectrometry system.Results: Diabetic patients had a higher level of C, C4, C6, C14, C18:2, and C18:2OH. Females had elevated C14:2 compared to the males. The C18:2 and C18:2OH levels were elevated as the Hb A1C level increased. The C18:2, C14OH were mostly increased in the prediabetic and diabetic patients, respectively.Conclusion: Increased ACs level indicates the increased acyl-CoA intermediates for the fatty acids and amino acids oxidation.

Kinetics of Serum Carnitine Fractions in Patients with Chronic Kidney Disease Not on Dialysis

BACKGROUND

Carnitine plays a pivotal role in energy synthesis through β-oxidation in mitochondria. Serum and tissue levels of free carnitine are significantly decreased in dialysis patients, whereas acylcarnitine levels are increased. However, the precise kinetics and fate of carnitine fractions in chronic kidney disease (CKD) patients who are not on dialysis have not been clarified. This study aims to determine the kinetics of serum carnitine fractions in patients who were not on dialysis.

METHODS

Seventy-five CKD patients not on dialysis were recruited in this study. Serum and urinary carnitine fraction levels were measured to evaluate the kinetics and regulation of serum carnitine fractions. Carnitine fractions were measured by the enzymatic cycling method.

RESULTS

Total and free serum carnitine levels did not change with progression of CKD, whereas acylcarnitine levels and the acyl/free carnitine ratio significantly increased. Serum acylcarnitine levels were inversely associated with estimated glomerular filtration rate (r² = 0.239, p < 0.001), but free carnitine levels were not. Serum free carnitine levels were positively associated with urinary free carnitine excretion (r² = 0.214, p < 0.001), but serum acylcarnitine levels were not. Multiple stepwise regression analysis revealed that urinary free carnitine excretion and blood urea nitrogen were independent determinants of serum free carnitine and acylcarnitine levels, respectively.

CONCLUSIONS

The present study demonstrated that serum acylcarnitine levels increased with renal dysfunction independent of urinary excretion levels. Serum free carnitine was not affected by renal function in CKD patients who were not on dialysis.

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

Background

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

Results

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

Conclusions

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

Supplementary Information

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

Newborn Screening and Genetic Analysis Identify Six Novel Genetic Variants for Primary Carnitine Deficiency in Ningbo Area, China

Primary carnitine deficiency (PCD) is an autosomal recessive disorder that could result in sudden death. It is caused by a defect in the carnitine transporter encoded by SLC22A5 (Solute Carrier Family 22 Member 5, MIM:603377). Currently, a number of variants in SLC22A5 have been identified, however, the PCD prevalence and its variants in Ningbo area are unclear. In this study, we screened 265,524 newborns by using tandem mass spectrometry. Variants in SLC22A5 were further detected by next-generation sequencing in individuals with abnormal free carnitine levels (C0). We identified 53 newborns with abnormal C0 levels and 26 with variants in SLC22A5. Among them, 16 with compound heterozygous or homozygous variants in SLC22A5 were diagnosed with PCD, suggesting the PCD birth prevalence in Ningbo city was 1/16,595. Moreover, the C0 level was significantly (P = 0.013) higher in PCD patients than in those with one variant. Besides, the c.1400C > G (p. S467C) and c.51C > G (p. F17L) variants were the most frequent and six novel variants are all predicted to be damaging. This study reports the largest PCD patients in Ningbo area by newborn screening and expands the variant spectrum of SLC22A5. Our findings demonstrate the clinical value of combining NBS program results with DNA analysis for the diagnosis of PCD.

An Examination of Serum Acylcarnitine and Amino Acid Profiles at Different Time Point of Ketogenic Diet Therapy and Their Association of Ketogenic Diet Effectiveness

Background: This study aimed to identify metabolic parameters at different time points of ketogenic diet therapy (KDT) and investigate their association with response to KDT in pediatric drug-resistant epilepsy (DRE). Methods: Prospectively, twenty-nine patients (0.67~20 years old) with DRE received classic ketogenic diet with non-fasting, gradual KD initiation protocol (GRAD-KD) for 1 year were enrolled. A total of 22 patients remaining in study received blood examinations at baseline, 3rd, 6th, 9th, and 12th months of KDT. β-hydroxybutyrate, free carnitine, acylcarnitines, and amino acids were compared between responders (seizure reduction rate ≥ 50%) and non-responders (seizure reduction rate < 50%) to identify the effectiveness of KDT. Results: The 12-month retention rate was 76%. The responders after 12 months of KDT were 59% (13/22). The free carnitine level decreased significantly at 9th months (p < 0.001) but increased toward baseline without symptoms. Propionyl carnitine (C3), Isovaleryl carnitine (C5), 3-Hydroxyisovalerylcarnitine (C5:OH) and methylmalonyl carnitine (C4-DC) decreased but 3-hydroxybutyrylcarnitine (C4:OH) increased significantly at 12th months of KDT. The glycine level was persistently higher than baseline after KDT. KDT responders had lower baseline C3 and long-chain acylcarnitines, C14 and C18, as well as lower C5, C18, and leucine/isoleucine. Conclusions: KDT should be avoided in patients with non-ketotic hyperglycemia. Routine carnitine supplementation is not recommended because hypocarnitinemia was transient and asymptomatic during KDT. Better mitochondrial βoxidation function associates with greater KDT response.

Perinatal free carnitine and short chain acylcarnitine blood concentrations in 12,000 full-term breastfed newborns in relation to their birth weight

BACKGROUND

Free carnitine (C0) and short chain acylcarnitine (SCA) blood concentrations play a significant role in fatty acid oxidation process during the first days of life. The aim of this study was to demonstrate C0 and SCA concentrations in Dried Blood Spots (DBS) of full term breastfed infants in relation to their birth weight (BW) perinatally.

METHODS

Breastfed full term infants (n = 12,000, 6000 males, 6000 females) with BW 2000-4000 g were divided into 4 equal groups: Group A, 2000-2500 g, B 2500-3000 g, C 3000-3500 g and D 3500-4000 g. Blood samples in the form of DBS were collected on the 3rd day of life and analyzed via a liquid chromatography tandem mass spectrometry (LC-MS/MS) protocol.

RESULTS

BW-related C0 and SCAs were found as follows: C0 was determined to be statistically significantly higher in group A (BW 2000-2500 g) in both males and females. Lower acetylcarnitine (C2) and hydroxybutyrylcarnitine (C4OH) blood concentrations were detected in group A of both sexes, whereas butyrylcarnitine (C4) concentrations were found to be lower in the same group of males only. Furthermore, high concentrations of C2 and C4OH were shown in group D (BW 3500-4000 g) in both sexes. SCA sum of means ± SD values in males and females of group A were statistically significantly lower as compared to other study groups.

CONCLUSION

Due to the number of the samples, data from this study could be applied as neonatal screening reference values for full term breastfed newborns in relation to their birth weight.

[Levels of blood free carnitine in preterm infants with different gestational ages and birth weights]

OBJECTIVE

To examine blood concentrations of free carnitine (FC) in preterm infants with different gestational ages (GA) and birth weights (BW).

METHODS

A total of 3 368 preterm infants were enrolled as subjects. According to GA, they were divided into extremely preterm birth (EPTB) group (GA <28 weeks; n=39), very preterm birth (VPTB) group (28 ≤GA <32 weeks; n=405), moderately preterm birth (MPTB) group (32 ≤GA <34 weeks; n=507), and late preterm birth (LPTB) group (34 ≤GA <37 weeks; n=2 417); according to BW, they were divided into extremely low birth weight (ELBW) group (BW <1 000 g; n=36), very low birth weight (VLBW) group (1 000 g ≤BW <1 500 g; n=387), low birth weight (LBW) group (1 500 g ≤BW <2 500 g; n=1 873), and normal birth weight (NBW) group (2 500 g ≤ BW <4 000 g; n=1 072). Blood concentrations of FC were measured between 72 hours and 7 days after birth.

RESULTS

The EPTB and VPTB groups had significantly higher FC concentrations than the MPTB and LPTB groups (P<0.05), and the MPTB group had significantly higher FC concentrations than the LPTB group (P<0.05). The lower limit of the 95% medical reference range of FC increased with the reduction in GA. The ELBW and VLBW groups had significantly higher FC concentrations than the LBW and NBW groups (P<0.05). The LBW group had significantly higher FC concentrations than the NBW group (P<0.05). The lower limit of the 95% medical reference range of FC increased with the reduction in BW.

CONCLUSIONS

There is a significant increase in blood FC concentrations in very/extremely preterm infants and very/extremely low birth weight infants, and tend to decrease with the increases in GA and BW.

Serum carnitine and acyl-carnitine in patients with meningitis due to tick-borne encephalitis virus infection

BACKGROUND

Hard ticks are the main vectors of tick-borne encephalitis virus (TBEV). Free carnitine (FC) and acylcarnitines (AC) have the basic role in β-oxidation as well as the modulation of immune and nervous system. Homeostasis of carnitines in the TBE patients was not studied so far.

OBJECTIVES

This study aimed to evaluate FC and AC serum concentrations in patients with meningitis due to TBEV infection before and after 14 ± 3 days of treatment.

MATERIAL AND METHODS

The study was performed in 14 patients aged 48 ± 29 years that were divided a posteriori (based on their FC level before and after treatment) into 2 subgroups: 1-8 and 9-14. Diagnosis was based on the neurological, serological and pleocytosis evaluation.

RESULTS

The FC level in patients 1-8 before treatment (24.1 ± 8.1) was significantly lower than in patients post-treatment (34.4 ± 8.3), lower than in the control group (40.5 ± 7.6), and lower than in patients 9-14 before treatment (40.0 ± 13.5) but not lower than in the patients 9-14 after treatment (24.7 ± 7.3 μmol/L), respectively, p < 0.05. AC concentration in the patients 1-8 before treatment (4.7 ± 2.2) was apparently lower than in patients post-treatment (9.5 ± 3.9 μmol/L) but the values were not significantly different. In patients 9-14 before treatment the AC concentration (16.3 ± 12.6) was higher than in patients after treatment (5.3 ± 4.0 μmol/L), but the difference was not statistically significant.

CONCLUSIONS

FC and AC homeostasis in circulation was disturbed in the patients with meningitis due to TBEV infection patients. The mean levels of FC and AC in 60% of the patients were below the normal range but normalized after treatment whereas in 40% of the patients they were near or at a normal range and significantly decreased after treatment. Explanation of this intriguing finding and its clinical significance is not easy without further studies.