Normal Levels of Plasma Free Carnitine and Acylcarnitines in Follow-Up Samples from a Presymptomatic Case of Carnitine Palmitoyl Transferase 1 (CPT1) Deficiency Detected Through Newborn Screening in Denmark

Clinical and Gene Analysis of Fatty Acid Oxidation Disorders Found in Neonatal Tandem Mass Spectrometry Screening

Objective

To investigate the clinical and gene mutation characteristics of fatty acid oxidative metabolic diseases found in neonatal screening.

Methods

A retrospective analysis was performed on 29,948 neonatal blood tandem mass spectrometry screening samples from January 2018 to December 2021 in our neonatal screening centre. For screening positive, recall review is still suspected of fatty acid oxidation metabolic disorders in children as soon as possible to improve the genetic metabolic disease-related gene detection package to confirm the diagnosis. All diagnosed children were followed up to the deadline.

Results

Among 29,948 neonates screened by tandem mass spectrometry, 14 cases of primary carnitine deficiency, six cases of short-chain acyl coenzyme A dehydrogenase deficiency, two cases of carnitine palmitoyltransferase-I deficiency and one case of multiple acyl coenzyme A dehydrogenase deficiency were recalled. Except for two cases of multiple acyl coenzyme A dehydrogenase deficiency that exhibited [manifestations], the other 21 cases were diagnosed pre-symptomatically. Eight mutations of SLC22A5 gene were detected, including c.51C>G, c.403G>A, c.506G>A, c.1400C>G, c.1085C>T, c.706C>T, c.1540G>C and c.338G>A. Compound heterozygous mutation of CPT1A gene c.2201T>C, c.1318G>A, c.2246G>A, c.2125G>A and ETFA gene c.365G>A and c.699_701delGTT were detected, and new mutation sites were found.

Conclusion

Neonatal tandem mass spectrometry screening is an effective method for identifying fatty acid oxidative metabolic diseases, but it should be combined with urine gas chromatography-mass spectrometry and gene sequencing technology. Our findings enrich the gene mutation profile of fatty acid oxidative metabolic disease and provide evidence for genetic counselling and prenatal diagnosis in families.

Use of Molecular Genetic Analyses in Danish Routine Newborn Screening

Historically, the analyses used for newborn screening (NBS) were biochemical, but increasingly, molecular genetic analyses are being introduced in the workflow. We describe the application of molecular genetic analyses in the Danish NBS programme and show that second-tier molecular genetic testing is useful to reduce the false positive rate while simultaneously providing information about the precise molecular genetic variant and thus informing therapeutic strategy and easing providing information to parents. When molecular genetic analyses are applied as second-tier testing, valuable functional data from biochemical methods are available and in our view, such targeted NGS technology should be implemented when possible in the NBS workflow. First-tier NGS technology may be a promising future possibility for disorders without a reliable biomarker and as a general approach to increase the adaptability of NBS for a broader range of genetic diseases, which is important in the current landscape of quickly evolving new therapeutic possibilities. However, studies on feasibility, sensitivity, and specificity are needed as well as more insight into what views the general population has towards using genetic analyses in NBS. This may be sensitive to some and could have potentially negative consequences for the NBS programme.

Novel mutation in carnitine palmitoyltransferase 1A detected through newborn screening for a presymptomatic case in China: a case report

Background

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a rare mitochondrial fatty acid oxidation (FAO) disorder that results in hypoketotic hypoglycemia and hepatic encephalopathy. It is caused by mutation in CPT1A. To date, only two symptomatic cases of CPT1A deficiency have been reported in China.

Case presentation

A newborn male, without any disease-related clinical manifestations, was diagnosed with CPT1A deficiency through newborn screening. Increased free carnitine levels and a significantly increased C0/(C16 + C18) ratio were detected by tandem mass spectrometry, and subsequently, mutations in CPT1A were found by gene sequence analysis. The patient was advised a low-fat, high-protein diet and followed up regularly. During three-years of follow-up since, the patient showed normal growth velocity and developmental milestones. Whole-exome sequence identified two mutations, c.2201 T > C (p.F734S) and c.1318G > A (p.A440T), in the patient. The c.2201 T > C mutation, which has been reported previously, was inherited from his father, while the c.1318G > A, a novel mutation, was inherited from his mother. The amino acid residues encoded by original sequences are highly conserved across different species. These mutations slightly altered the three-dimensional structure of the protein, as analyzed by molecular modeling, suggesting that they may be pathogenic.

Conclusion

This is the first case of CPT1A deficiency detected through newborn screening based on diagnostic levels of free carnitine, in China. Three years follow-up suggested that early diagnosis and diet management may improve the prognosis in CPT1A patient. In addition, we identified a novel mutation c.1318G > A in CPT1A,and a possible unique to Chinese lineage mutation c.2201 T > C. Our findings have expanded the gene spectrum of this rare condition and provided a basis for family genetic counseling and prenatal diagnosis.

Three Novel and One Potential Hotspot CPT1A Variants in Chinese Patients With Carnitine Palmitoyltransferase 1A Deficiency

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is an inherited disorder of mitochondrial fatty acid β-oxidation that impairs fasting ketogenesis and gluconeogenesis in the liver. Few studies implementing newborn screening (NBS) for CPT1A deficiency in the Chinese population have been reported. This study aimed to determine the biochemical, clinical, and genetic characteristics of patients with CPT1A deficiency in China. A total of 204,777 newborns were screened using tandem mass spectrometry at Quanzhou Maternity and Children's Hospital between January 2017 and December 2018. Newborns with elevated C0 levels were recruited, and suspected patients were subjected to further genetic analysis. Additionally, all Chinese patients genetically diagnosed with CPT1A deficiency were reviewed and included in the study. Among the 204,777 screened newborns, two patients were diagnosed with CPT1A deficiency; thus, the estimated incidence in the selected population was 1:102,388. In addition to the two patients newly diagnosed with CPT1A deficiency, we included in our cohort 10 Chinese patients who were previously diagnosed. Five of these 12 patients were diagnosed via NBS. All patients exhibited elevated C0 and/or C0/(C16+C18) ratios. No clinical symptoms were observed in the five patients diagnosed via NBS, while all seven patients presented with clinical symptoms, including fever, cough, vomiting, diarrhea, and seizures. Eighteen distinct CPT1A variants were identified, 15 of which have been previously reported. The three novel variants were c.272T>C (p.L91P), c.734G>A (p.R245Q), and c.1336G>A (p.G446S). in silico analysis suggested that all three novel variants were potentially pathogenic. The most common variant was c.2201T>C (p.F734S), with an allelic frequency of 16.67% (4/24). Our findings demonstrated that NBS for CPT1A deficiency is beneficial. The three novel variants expand the mutational spectrum of CPT1A in the Chinese population, and c.2201T>C (p.F734S) may be a potential hotspot CPT1A mutation.

Disorders of mitochondrial long-chain fatty acid oxidation and the carnitine shuttle

Mitochondrial fatty acid oxidation is an essential pathway for energy production, especially during prolonged fasting and sub-maximal exercise. Long-chain fatty acids are the most abundant fatty acids in the human diet and in body stores, and more than 15 enzymes are involved in long-chain fatty acid oxidation. Pathogenic mutations in genes encoding these enzymes result in a long-chain fatty acid oxidation disorder in which the energy homeostasis is compromised and long-chain acylcarnitines accumulate. Symptoms arise or exacerbate during catabolic situations, such as fasting, illness and (endurance) exercise. The clinical spectrum is very heterogeneous, ranging from hypoketotic hypoglycemia, liver dysfunction, rhabdomyolysis, cardiomyopathy and early demise. With the introduction of several of the long-chain fatty acid oxidation disorders (lcFAOD) in newborn screening panels, also asymptomatic individuals with a lcFAOD are identified. However, despite early diagnosis and dietary therapy, a significant number of patients still develop symptoms emphasizing the need for individualized treatment strategies. This review aims to function as a comprehensive reference for clinical and laboratory findings for clinicians who are confronted with pediatric and adult patients with a possible diagnosis of a lcFAOD.

Biochemical screening of 504,049 newborns in Denmark, the Faroe Islands and Greenland--experience and development of a routine program for expanded newborn screening

Expanded newborn screening for selected inborn errors of metabolism (IEM) in Denmark, the Faroe Islands and Greenland was introduced in 2002. We now present clinical, biochemical, and statistical results of expanded screening (excluding PKU) of 504,049 newborns during nine years as well as diagnoses and clinical findings in 82,930 unscreened newborns born in the same period. The frequencies of diagnoses made within the panel of disorders screened for are compared with the frequencies of the disorders in the decade preceding expanded newborn screening. The expanded screening was performed as a pilot study during the first seven years, and the experience obtained during these years was used in the development of the routine neonatal screening program introduced in 2009. Methods for screening included tandem mass spectrometry and an assay for determination of biotinidase activity. A total of 310 samples from 504,049 newborns gave positive screening results. Of the 310 results, 114 were true positive, including results from 12 newborns in which the disease in question was subsequently diagnosed in their mothers. Thus, the overall frequency of an IEM in the screening panel was 1:4942 (mothers excluded) or 1:4421 (mothers included). The false positive rate was 0.038% and positive predictive value 37%. Overall specificity was 99.99%. All patients with true positive results were followed in The Center for Inherited Metabolic Disorders in Copenhagen, and the mean follow-up period was 45 months (range 2109 months). There were no deaths among the 102 children, and 94% had no clinically significant sequelae at last follow-up. Our study confirms the higher frequency of selected IEM after implementation of expanded newborn screening and suggests an improved outcome for several disorders. We argue that newborn screening for these disorders should be standard of care, though unresolved issues remain, e.g. about newborns with a potential for remaining asymptomatic throughout life. Well organized logistics of the screening program from screening laboratory to centralized, clinical management is important.