Incorporating second-tier genetic screening for multiple acyl-CoA dehydrogenase deficiency.

BACKGROUND: Newborn screening (NBS) for multiple acyl-CoA dehydrogenase deficiency (MADD) has poor sensitivity. This study aimed to evaluate the feasibility of incorporating second-tier genetic screening for MADD. METHODS: A total of 453,390 newborns were screened for inherited metabolic disorders using tandem mass spectrometry from January 2017 to May 2022. A matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) assay was developed to identify 23 common ETFDH variants and used for second-tier screening of MADD. RESULTS: Overall, 185 newborns with suspected MADD received second-tier genetic screening. Thirty-three (17.8 %) newborns with positive results, of which 7 were homozygotes, 5 were compound heterozygotes, 21 were heterozygotes. Further genetic analysis revealed that 6 of the 21 newborns had a second ETFDH variant. Therefore, 18 patients were finally diagnosed with MADD, with a positive predictive value of 9.73 %. The detection rate and diagnostic rate of MALDI-TOF MS assay were 83.33 % and 66.67 %, respectively. Thus the incidence of MADD in our population was estimated at 1:25,188. Nine different ETFDH variants were identified in MADD patients. The most common ETFDH variant being c.250G > A with an allelic frequency of 47.22 %, followed by c.524G > A (13.89 %) and c.998A > G (13.89 %). All patients had elevation of multiple acylcarnitines at NBS. However, seven patients had normal acylcarnitine levels and two patients showed mild elevation of only two acylcarnitines during the recall review. CONCLUSION: We have established a high throughput MALDI-TOF MS assay for MADD screening. Half of the MADD patients would not be detected under conventional screening protocols. Incorporating second-tier genetic screening into the current NBS could improve the performance of MADD NBS.

Newborn screening and genetic features of patients with hyperphenylalaninemia in a southern Chinese population.

BACKGROUND AND AIMS: Hyperphenylalaninemia (HPA) is the most common congenital amino acid metabolism-related defect, but its incidence differs substantially between northern and southern China. We aimed to elucidate the incidence, proportion, and genetic features of HPA in a southern Chinese population. MATERIALS AND METHODS: We analyzed the HPA screening results for 580,460 newborns from 2014 to 2021. RESULTS: Of the 296 newborns who tested HPA positive, 56 were diagnosed with HPA, including 47 with phenylalanine hydroxylase deficiency and nine with tetrahydrobiopterin deficiency (BH4D). HPA incidence was estimated to be 1:10,365 newborns. All patients had elevated Phe and Phe/Tyr levels. Thirty-three PAH variants and five PTS variants were detected in HPA patients; 80.6 % PAH variants and 100 % PTS variants were classified as pathogenic or likely pathogenic. In silico tools predicted the remaining variants to be damaging. PAH variants clustered in exons 3, 5, 7, 11, and 12 and PTS variants clustered in exons 2 and 5. The most common PAH variants were c.158G > A (p.R53H, 22.3 %) and c.721C > T (p.R241C, 14.9 %). The most common PTS variants were c.155A > G (p.N52S, 50.0 %) and c.259C > T (p.P87S, 33.3 %). CONCLUSION: Newborn screening is an effective method for early detection of HPA, but differential diagnosis of BH4D is necessary.

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.

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 ß-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.

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.

Newborn screening and molecular features of patients with multiple acyl-CoA dehydrogenase deficiency in Quanzhou, China.

OBJECTIVES: Multiple acyl-CoA dehydrogenase deficiency (MADD) is an autosomal recessive disorder of fatty acid, amino acid and choline metabolism. Late-onset MADD is caused by ETFDH mutations and is the most common lipid storage myopathy in China. However, few patients with MADD have been identified through newborn screening (NBS). This study assessed the acylcarnitine profiles and molecular features of patients with MADD identified through NBS. METHODS: From January 2014 to June 2020, 479,786 newborns screened via tandem mass spectrometry were recruited for this study. Newborns with elevated levels of multiple acylcarnitines were recalled, those who tested positive in the reassessment were referred for genetic analysis. RESULTS: Of 479,786 newborns screened, six were diagnosed with MADD. The MADD incidence in the Chinese population was estimated to be 1:79,964. Initial NBS revealed five patients with typical elevations in the levels of multiple acylcarnitines; however, in one patient, acylcarnitine levels were in the normal reference range during recall. Notably, one patient only exhibited a mildly increased isovalerylcarnitine (C5) level at NBS. The patient with an atypical acylcarnitine profile was diagnosed with MADD by targeted gene sequencing. Six distinct ETFDH missense variants were identified, with the most common variant being c.250G>A (p.A84T), with an allelic frequency of 58.35 (7/12). CONCLUSIONS: These findings revealed that it is easy for patients with MADD to go unidentified, as they may have atypical acylcarnitine profiles at NBS and the recall stage, indicating the value of genetic analysis for confirming suspected inherited metabolic disorders in the NBS program. Therefore, false-negative (FN) results may be reduced by combining tandem mass spectrometry (MS/MS) with genetic testing in NBS for MADD.

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.

Combined primary carnitine deficiency with neonatal intrahepatic cholestasis caused by citrin deficiency in a Chinese newborn.

BACKGROUND: Primary carnitine deficiency (PCD) is an autosomal recessive disorder affecting the carnitine cycle and resulting in defective fatty acid oxidation. Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is an autosomal recessive disorder and one of the main causes of inherited neonatal cholestasis. Both PCD and NICCD are included in the current expanded newborn screening (NBS) targets. CASE PRESENTATION: Targeted exome sequencing was performed on a Chinese proband, and Sanger sequencing was utilised to validate the detected mutations. The patient who was initially suspected to have PCD based on the NBS results presented with neonatal intrahepatic cholestasis and ventricular septal defect. Further investigations not only confirmed PCD but also revealed the presence of NICCD. Four distinct mutations were detected, including c.51C > G (p.F17L) and c.760C > T (p.R254X) in SLC22A5 as well as c.615 + 5G > A and IVS16ins3kb in SLC25A13. CONCLUSIONS: This is the first reported case of PCD and NICCD occurring in the same patient. The dual disorders in a newborn broaden our understanding of inherited metabolic diseases. Thus, this study highlighted the importance of further genetic testing in patients presenting with unusual metabolic screening findings.

Clinical, biochemical, and genetic analysis of a Chinese Han pedigree with holocarboxylase synthetase deficiency: a case report.

BACKGROUND: Holocarboxylase synthetase (HLCS) deficiency is a rare inborn disorder of biotin metabolism, which results in defects in several biotin-dependent carboxylases and presents with metabolic ketoacidosis and skin lesions. CASE PRESENTATION: In this paper, we report a Chinese Han pedigree with HLCS deficiency diagnosed by using next-generation sequencing and validated with Sanger sequencing of the HLCS and BTD genes. The Chinese proband carries the common missense mutation c.1522C > T (p.Arg508Trp) in exon 9 of the HLCS gene, which generates an increased Km value for biotin. A novel frameshift mutation c.1006_1007delGA (p.Glu336Thrfs*15) in exon 6 of the HLCS gene is predicted to be deleterious through PROVEAN and MutationTaster. A novel heterozygous mutation, c.638_642delAACAC (p.His213Profs*4), in the BTD gene is also identified. CONCLUSIONS: The Chinese proband carries the reported Arg508Trp variant, the novel 2-bp frameshift mutation c.1006_1007delGA (p.Glu336Thrfs*15), which expands the mutational spectrum of the HLCS gene, and the novel heterozygous mutation c.638_642delAACAC (p.His213Profs*4), which expands the mutational spectrum of the BTD gene. Furthermore, reversible hearing damage is rarely reported in patients with HLCS deficiency, which deserves further discussion.

Newborn screening and genetic characteristics of patients with short- and very long-chain acyl-CoA dehydrogenase deficiencies.

BACKGROUND AND AIMS: Acyl-CoA dehydrogenase deficiencies are a group of mitochondrial fatty-acid oxidation disorders rarely reported in mainland China. We assessed the biochemical and genetic characteristics of patients with short- and very-long-chain-acyl-CoA dehydrogenase deficiencies (SCADD/VLCADD) discovered through newborn screening. MATERIALS AND METHODS: We investigated the effects of genetic variations on protein function using in silico prediction and structural modelling. RESULTS: Of 364,545 screened newborns, four were diagnosed with SCADD and four with VLCADD. SCADD and VLCADD incidences in our population were 1:91,136. All patients exhibited elevated C4 or C14:1 levels. Three SCADD patients had increased urinary ethylmalonic acid concentrations. Six ACADS and eight ACADVL variants were identified, with no hotspot variants, and five were unreported, including four missense variants and one splice site variant. ACADVL c.1434 + 2 T > C is a splice site variant that could affect splicing, leading to exon 14 skipping. In silico tools predicted the missense variants as pathogenic. Structural modelling confirmed that the missense variants may affect quaternary structures, causing protein instability. CONCLUSIONS: Our findings expanded the ACADS and ACADVL mutational spectra. The combination of in silico prediction and structural modelling can improve our understanding of the pathogenicity of unreported genetic variants, providing an explanation for variant assessment.

Newborn screening for isovaleric acidemia in Quanzhou, China.

BACKGROUND: Isovaleric acidemia (IVA) is a rare autosomal recessive disorder of leucine metabolism caused by a defective isovaleryl-CoA dehydrogenase (IVD) gene. Reports of IVA diagnoses following newborn screening (NBS) in the Chinese population are few. METHODS: We investigated the biochemical, clinical, and molecular profiles of 5 patients with IVA in China. The estimated incidence of IVA in Quanzhou, China is 1 in 1:84,469. RESULTS: Initial NBS revealed mild to markedly increased isovalerylcarnitine (C5) concentrations in all 5 patients, and differential diagnosis revealed increased urinary isovaleryglycine concentrations in 2 patients. One patient presented with acute neonatal symptoms, whereas the other 4 remained asymptomatic. Eight distinct IVD gene variants were identified. The most common variant was c.1208A > G (p.Y403C), with an allele frequency of 30%. Five variants were previously unreported, namely, c.499A > G (p.M167V), c.640A > G (p.T214A), c.740G > A (p.G247E), c.832G > C (p.V278L), and c.1195G > C (p.D399H). Different in silico prediction analyses suggested that these previously unreported missense variants are pathogenic. Protein modelling analyses also showed that these missense variants may cause structural damage and dysfunction in IVD. CONCLUSIONS: Patients with IVA may have C5 concentrations approaching the cut-off values, highlighting the need for stringent recall criteria and second-tier tests to improve screening performance.

Clinical and genetic analysis of five Chinese patients with urea cycle disorders.

BACKGROUND: The urea cycle plays a key role in preventing the accumulation of toxic nitrogenous waste products, including two essential enzymes: ornithine transcarbamylase (OTC) and argininosuccinate lyase (ASL). Ornithine transcarbamylase deficiency (OTCD) results from mutations in the OTC. Meanwhile, argininosuccinate lyase deficiency (ASLD) is caused by mutations in the ASL. METHODS: Blood tandem mass spectrometric analysis and urea organic acidemia screening were performed on five Chinese cases, including three OTCD and two ASLD patients. Next-generation sequencing was then used to make a definite diagnosis, and the related variants were validated by Sanger sequencing. RESULTS: The five patients exhibited severe clinical symptoms, with abnormal biochemical analysis and amino acids profile. Genetic analysis revealed two variants [c.77G>A (p.Arg26Gln); c.116G>T (p.Gly39Val)] in the OTC, as well as two variants [c.1311T>G (p.Tyr437*); c.961T>A (p.Tyr321Asn)] in the ASL. Conservation analysis showed that the amino acids of the two novel mutations were highly conserved in different species and were predicted to be possibly damaging with several in silico prediction programs. 3D-modeling analysis indicated that the two novel missense variants might result in modest distortions of the OTC and ASL protein structures, respectively. CONCLUSIONS: Two novel variants expand the mutational spectrums of the OTC and ASL. All the results may contribute to a better understanding of the clinical course and genetic characteristics of patients with urea cycle disorders.

[Characteristics of gene variants among patients with hyperphenylalaninemia from Quanzhou region of Fujian province].

OBJECTIVE: To explore the spectrum of genetic variants among patients with hyperphenylalaninemia (HPA) from Quanzhou area of Fujian province. METHODS: For 63 children affected with HPA, next generation sequencing was used to identify potential variants in PAH, PTS, PCBD1, QDPR, SPR and GCH1 genes. RESULTS: Fifty two variants underlying phenylalanine hydroxylase deficiency (PAHD) and 13 variants underlying 6-pyruvoyl tetrahydropterin synthase deficiency (PTPSD) were identified. Two patients carried variants of both PAH and PTS genes. The most common variants of the PAH gene were R53H (21.69%), R241C(18.07%), R243Q(12.05%) and EX6-96A to G (7.23%), which were mainly located in exons 7 (32.53%), 2 (21.69%), 6 (9.64%) and 12 (9.64%). The L227M variant of the PAH gene was unreported previously. N52S (35.00%), P87S (25.00%), IVS1-291A to G (10.00%) and T67M (10.00%) variants were the most common variants for the PTS gene and were mainly located in exons 2 (35.00%) and 5 (35.00%). CONCLUSION: The variant spectrum underlying HPA in Quanzhou area showed a geographical specificity. A novel variant of the PAH gene (L227M) has been detected.

Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening.

Short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) is an autosomal recessive disorder of impaired isoleucine catabolism caused by mutations in the ACADSB gene. There are limited SBCADD cases worldwide and to date no Chinese patients with SBCADD have been reported. The aim of this study was to investigate the biochemical, clinical information, and genotypes of twelve patients with SBCADD in China for the first time. The estimated incidence of SBCADD was 1 in 30,379 in Quanzhou, China. The initial newborn screening (NBS) results revealed that all patients showed slightly or moderately elevated C5 concentrations with C5/C2 and C5/C3 ratios in the reference range, which has the highest risk of being missed. All patients who underwent urinary organic acid analysis showed elevation of 2-methylburtyrylglycine in urine. All patients were asymptomatic at diagnosis, and had normal growth and development during follow-up. Eight different variants in the ACADSB gene, including five previously unreported variants were identified, namely c.596A > G (p.Tyr199Cys), c.653T > C (p.Leu218Pro), c.746del (p.Pro249Leufs*15), c.886G > T (p.Gly296*) and c.923G > A (p.Cys308Tyr). The most common variant was c.1165A > G (33.3%), followed by c.275C > G (20.8%). All previously unreported variants may cause structural damage and dysfunction of SBCAD, as predicted by bioinformatics analysis. Thus, our findings indicate that SBCADD may be more frequent in the Chinese population than previously thought and newborn screening, combined with genetic testing is important for timely diagnosis. Although the clinical course of Chinese patients with SBCADD is likely benign, longitudinal follow-up may be helpful to better understand the natural history of SBCADD.

Citrullinemia type I is associated with a novel splicing variant, c.773 + 4A > C, in ASS1: a case report and literature review.

BACKGROUND: Citrullinemia type I (CTLN1) is a rare autosomal recessive disorder of the urea cycle caused by a deficiency in the argininosuccinate synthetase (ASS1) enzyme due to mutations in the ASS1 gene. Only a few Chinese patients with CTLN1 have been reported, and ASS1 gene mutations have been identified sporadically in China. CASE PRESENTATION: A Chinese family with one member affected with mild CTLN1 was enrolled. Targeted exome sequencing was performed on the proband, and Sanger sequencing was used to validate the detected mutation. We also reviewed the genetic and clinical characteristics of CTLN1 in Chinese patients that have been published to date. Newborn screening showed remarkably increased concentrations of citrulline with elevated ratios of citrulline/arginine and citrulline/phenylalanine, and the patient presented with a speech delay at age three. The urinary organic acid profiles were normal. A novel homozygous splicing variant c.773 + 4A > C in the ASS1 gene was identified in the proband, and it was predicted to affect splicing by in silico analysis. To date, only nine Chinese patients with CTLN1 have been reported, with a total of 15 ASS1 mutations identified and no high frequency or hot spot mutations found; the mutation spectrum of Chinese patients with CTLN1 was heterogeneous. CONCLUSIONS: We described a mild Chinese CTLN1 case with a novel homozygous splicing variant c.773 + 4A > C and reviewed previous genotypes and phenotypes in Chinese patients with CTLN1. Thus, our findings contribute to understanding the molecular genetic background and clinical phenotype of CTLN1 in this population.

Expanded newborn screening for inherited metabolic disorders and genetic characteristics in a southern Chinese population.

To evaluate the incidence, disease spectrum, and genetic characteristics of inherited metabolic disorders (IMDs) of newborns in Quanzhou area, China. We analyze the expanded newborn screening results of IMDs detected by tandem mass spectrometry (MS/MS) during 5 years. Suspected positive patients were diagnosed through next-generation sequencing and validated by Sanger sequencing. In addition, multiplex ligation-dependent probe amplification technology has also been applied to assist in diagnosis of diseases with deletion or duplication mutations. A total of 364,545 newborns were screened, 130 IMDs were identified yielding an incidence of 1:2804. In addition, 9 cases of maternal disorders were also identified by our MS/MS newborn screening program. There were 42 newborns with amino acid disorders (1:8680), 39 with organic acid disorders (1:9347), and 49 with fatty acid oxidation disorders (1:7440). Unlike other studies, our study indicated that fatty acid oxidation disorder has the highest proportion (37.7%), particularly primary carnitine deficiency (PCD) with incidence up to 1:10,126 was the most common disorder in the region. The recurrent mutations of relatively common diseases like PCD, phenylalanine hydroxylase deficiency, short-chain acyl-CoA dehydrogenase deficiency, citrin deficiency, glutaric acidemia type I, isobutyryl-CoA dehydrogenase deficiency, and multiple acyl-CoA dehydrogenase deficiency in this region were also clearly elucidated. Therefore, our data indicated that IMDs are never uncommon in Quanzhou, the disease spectrum and genetic backgrounds were clearly elucidated, contributing to the treatment and prenatal genetic counseling of these disorders in this region.

Clinical, biochemical and genetic analysis of Chinese patients with isobutyryl-CoA dehydrogenase deficiency.

Isobutyryl-CoA dehydrogenase deficiency (IBDHD) is a rare autosomal recessive metabolic disorder related to valine catabolism and results from variants in ACAD8. Here, we present the clinical, biochemical, and genotypes of seven patients with IBDHD in China for the first time. Five patients remained asymptomatic during follow-up, whereas one juvenile had speech delay and one newborn exhibited clinical symptoms. All patients showed remarkably increased concentrations of C4-aclycarnitine with elevated C4/C2 and C4/C3 ratios. In urine organic acid tests, only one patient presented with an increased concentration of isobutyrylglycine excretion. Genetic testing was performed to detect the causative variants. Five previously unreported variants, c.235C > G, c.286G > A, c.444G > T c.1092 + 1G > A, and c.1176G > T, and one known variant, c.1000C > T, in ACAD8 were identified. These previously unreported variants in ACAD8 were predicted to be disease-causing and the c.1092 + 1G > A variant was confirmed to cause skipping of exon 9 by reverse transcription PCR. The most common variant was c.286G > A, which showed an allelic frequency of 50% (7/14), and thus may be a prevalent variant among Chinese patients. Our results broaden the mutational spectrum of ACAD8 and improve the understanding of the clinical phenotype of IBDHD.

Mild clinical features of isolated methylmalonic acidemia associated with a novel variant in the MMAA gene in two Chinese siblings.

BACKGROUND: Methylmalonic acidemia (MMA) is an autosomal recessive inherited disorder caused by complete or partial deficiency of the enzyme methylmalonyl-CoA mutase (mut0 enzymatic subtype or mut- enzymatic subtype, respectively); a defect in the transport or synthesis of its cofactor, adenosyl-cobalamin (cblA, cblB, or cblD-MMA); or deficiency of the enzyme methylmalonyl-CoA epimerase. The cblA type of MMA is very rare in China. This study aimed to describe the biochemical, clinical, and genetic characteristics of two siblings in a Chinese family, suspected of having the cblA-type of MMA. METHODS: The Chinese family of Han ethnicity of two siblings with the cblA-type of MMA, was enrolled. Target-exome sequencing was performed for a panel of MMA-related genes to detect causative mutations. The influence of an identified missense variant on the protein's structure and function was analysed using SIFT, PolyPhen-2, PROVEAN, and MutationTaster software. Moreover, homology modelling of the human wild-type and mutant proteins was performed using SWISSMODEL to evaluate the variant. RESULTS: The proband was identified via newborn screening (NBS); whereas, her elder brother, who had not undergone expanded NBS, was diagnosed later through genetic family screening. The younger sibling exhibited abnormal biochemical manifestations, and the clinical performance was relatively good after treatment, while the older brother had a mild biochemical and clinical phenotype, mainly featuring poor academic performance. A novel, homozygous missense c.365T>C variant in exon 2 of their MMAA genes was identified using next-generation sequencing and validated by Sanger sequencing. Several different types of bioinformatics software predicted that the novel variant c.365T>C (p.L122P) was deleterious. Furthermore, three-dimensional crystal structure analysis revealed that replacement of Leu122 with Pro122 led to the loss of two intramolecular hydrogen bonds between the residue at position 122 and Leu188 and Ala119, resulting in instability of the MMAA protein structure. CONCLUSIONS: The two siblings suspected of having the cblA-type of MMA showed mild phenotypes during follow-up, and a novel, homozygous missense variant in their MMAA genes was identified. We believe that the clinical features of the two siblings were associated with the MMAA c.365T>C variant; however, further functional studies are warranted to confirm the variant's pathogenicity.

[Detection of GCDH mutations in five Chinese patients with glutaric acidemia type I].

OBJECTIVE To detect potential mutations of GCDH gene in five patients with glutaric acidemia type I (GA-I). METHODS Genomic DNA was extracted from peripheral blood samples from the patients. The 11 exons and their flanking sequences of the GCDH gene were amplified with PCR and subjected to direct sequencing. RESULTS Four mutations of the GCDH gene were identified among the patients, which included c.532G>A (p.G178R), c.533G>A (p.G178E), c.106_107delAC (p.Q37fs*5) and c.1244-2A>C. Among these, c.1244-2A>C was the most common, while c.106_107delAC was a novel mutation, which was predicted to be pathogenic by MutationTaster software. CONCLUSION The diagnosis of GA-I has been confirmed in all of the five patients. Identification of the novel GCDH mutations has enriched the mutational spectrum of the GCDH gene.