ObjectiveWhole exome sequencing (WES) is becoming more widely used as a diagnostic tool in the field of medicine. In this article, we reported the diagnostic yield of WES and mitochondrial genome assessment in 2226 consecutive cases in a single clinical laboratory.Materials and methodsWe retrospectively analyzed consecutive WES reports from 2226 patients with various genetic disorders. WES- process was focused exclusively on the probands and aimed at a higher diagnostic capacity. We determined the diagnostic rate of WES overall and by phenotypic category, mode of inheritance, mitochondrial genome variant, and copy number variants (CNVs).ResultsAmong the 2226 patients who had diagnostic WES proband-only, the overall diagnostic yield of WES was 34.59% (770/2226). The highest diagnostic yield was observed in autosomal dominant disorders, at 45.58% (351/770), followed by autosomal recessive at 31.95%(246/770), X-linked disorder at 9.61%(74/770), and mitochondrial diseases at a notably lower 0.65%(5/770). The 12.21% (94/770) diagnoses were based on a total of 94 copy number variants reported from WES data. CNVs in children accounted for 67.02% of the total CNVs. While majority of the molecular diagnoses were related to nuclear genes, the inclusion of mitochondrial genome sequencing in the WES test contributed to five diagnoses. all mitochondrial diseases were identified in adults.ConclusionsThe proband-only WES provided a definitive molecular diagnosis for 34.59% of a large cohort of patients while analysis of WES simultaneously analyzed the SNVs, exons, mitochondrial genome, and CNVs, thereby improving the diagnostic yield significantly compared to the single-detection WES method; and facilitating the identification of novel candidate genes.

OBJECTIVE:To summarize the results of prenatal diagnosis and outcome of pregnancy of fetuses with a high risk for 6p22.1.1-p21.32 duplication signaled by non-invasive prenatal screening (NIPS). METHODS:Clinical information, results of prenatal diagnosis and pregnancy for fetuses with a high risk for 6p22.1-p21.32 duplication were collected and analyzed. This study has been approved by the Medical Ethics Committee of the First Affiliated Hospital of Zhengzhou University (Ethic No. 2018-YB-08). RESULTS:Forty three pregnant women with a high risk for 6p22.1-p21.32 duplication were identified by NIPS, among whom 30 had accepted invasive prenatal diagnosis, and 27 fetuses were verified to be false positive. Three fetuses were found to have other chromosomal abnormalities, among whom two were rated to be likely benign CNV and 1 was rated to be likely pathogenic. Follow up of the 43 pregnant women revealed that 35 fetuses were normal after birth, 1 pregnancy was terminated, and 7 were lost to follow up. CONCLUSION:For pregnant women with a high risk for 6p22.1-p21.32 duplication signaled by NIPS, genetic counselor need to inform them the high false positive rate and recommend invasive prenatal diagnosis and/or ultrasound examination in order to reduce the psychological and economic burdens.

This study aims to assess the feasibility of detecting and diagnosing Duchenne muscular dystrophy (DMD) during prenatal screening for chromosome abnormalities using cell-free fetal DNA extracted from peripheral blood samples of pregnant women.Two pregnant women identified as high risk through noninvasive prenatal testing (NIPT) underwent amniocentesis to obtain fetal cells. Subsequent fetal chromosomal karyotyping was conducted, and genomic DNA from fetal cells was extracted for copy number variation sequencing (CNV-Seq) analysis, complemented by multiplex ligation-dependent probe amplification (MLPA) to detect deletions or duplications within the DMD gene.NIPT results for the two samples indicated potential abnormalities involving chromosomes 21 and 18. However, karyotype analysis of the fetuses revealed no abnormalities. CNV-Seq identified deletions of 0.28 and 0.18 Mb within chromosome Xp21.1, encompassing the DMD gene, in each fetus. In family 1, MLPA results indicated a maternal heterozygous deletion spanning exons 12 to 41 in the DMD gene, while the fetus exhibited deletions in exons 12 to 41. In family 2, MLPA results confirmed normal DMD gene status in the pregnant woman's peripheral blood genomic DNA but revealed a fetal deletion spanning exons 48 to 52. Both fetuses were diagnosed with DMD and subsequently underwent termination.Abnormalities identified through NIPT necessitate further invasive prenatal diagnostic procedures. For cases involving chromosomal microdeletions or microduplications, a combination of karyotyping and CNV-Seq testing is essential for comprehensive diagnosis. NIPT followed by CNV-Seq may offer insights into large exon deletions within the DMD gene in specific instances. · NIPT results can offer valuable insights into the deletion and duplication of DMD gene for the fetus.. · It's crucial to notice unexpected findings in NIPT.. · A combination of karyotyping and CNV-Seq testing is essential for comprehensive diagnosis..

OBJECTIVE:To explore the genetic etiology of a child with delayed growth and development and carry out a literature review.METHODS:A child suspected for Al Kaissi syndrome at the First Affiliated Hospital of Zhengzhou University on March 6, 2021 was selected as the study subject. Following extraction of genomic DNA, the child was subjected to copy number variation sequencing (CNV-seq) and whole exome sequencing (WES), and candidate variants were verified by PCR-agarose gel electrophoresis and quantitative real-time PCR (qPCR). Prenatal diagnosis was conducted on chorionic villi sample upon subsequent pregnancy.RESULTS:The child, a 6-year-and-4-month-old boy, has dysmorphic features including low-set protruding ears and triangular face, delayed language and intellectual development, and ventricular septal defect. CNV-seq result has found no obvious abnormality, whilst WES revealed homozygous deletion of exons 1 and 2 of the CDK10 gene, which was confirmed by PCR-agarose gel electrophoresis and qPCR. Both of his parents were heterozygous carriers. Prenatal diagnosis using chorionic villi samples suggested that the fetus also carried the heterozygous deletion.CONCLUSION:The clinical features of Al Kaissi syndrome in this child can probably be attributed to the homozygous deletion of exons 1 and 2 of the CDK10 gene.

Clinical application of serological screening and non-invasive prenatal testing (NIPT) both have difficulties to attain high detection rate and low cost. For its advantages of high detection rate, high sensitivity, simplicity, short turnaround time and low cost, digital PCR (dPCR) has provided a new choice for prenatal screening of trisomies 21, 18 and 13. To standardize the application of dPCR for prenatal screening, we have formulated this consensus by referring to relevant guidelines, expert consensus and latest literature, which has covered the basic requirements, application scope, pre-testing service, testing procedure, report interpretation, genetic counseling, and limitations for this technology.

OBJECTIVE:To analyze the result of prenatal diagnosis and outcome of pregnancy for fetuses with rare autosomal trisomies (RATs) suggested by non-invasive prenatal testing (NIPT).METHODS:A total of 69 608 pregnant women who underwent NIPT at Genetics and Prenatal Diagnosis Center of the First Affiliated Hospital of Zhengzhou University from January 2016 to December 2020 were selected as study subjects. The result of prenatal diagnosis and outcome of pregnancy for those with a high risk for RATs were retrospectively analyzed.RESULTS:Among the 69 608 pregnant women, the positive rate of NIPT for high-risk RATs was 0.23% (161/69 608), with trisomy 7 (17.4%, 28/161) and trisomy 8 (12.4%, 20/161) being the most common, and trisomy 17 (0.6%, 1/161) being the rarest. For 98 women who had accepted invasive prenatal diagnosis, 12 fetal chromosomal abnormalities were confirmed, and in 5 cases the results were consistent with those of NIPT, which yielded a positive predictive value of 5.26%. Among the 161 women with a high risk for RATs, 153 (95%) were successfully followed up. 139 fetuses were ultimately born, with only one being clinically abnormal.CONCLUSION:Most women with a high risk for RATs by NIPT have good pregnancy outcomes. Invasive prenatal diagnosis or serial ultrasonography to monitor fetal growth, instead of direct termination of pregnancy, is recommended.

目的:探讨游离胎儿DNA比例(FF)的影响因素及其与染色体异常疾病的相关性.方法:回顾分析孕妇年龄、孕周、体质量指数以及NIPS提示高风险胎儿与FF的关系.结果:FF主要分布范围是4％ ～25％.FF与孕周呈正相关,与孕妇年龄和体质量指数呈负相关.单胎胎儿的FF高于双/多胎妊娠胎儿,自然妊娠胎儿的FF高于辅助生殖妊娠胎儿,差异均有统计学意义(P<0.05).高风险胎儿的FF高于低风险胎儿,差异均有统计学意义(P<0.05).21、18和13-三体综合征的Z值与FF呈正相关.性染色体组真阳性和假阳性胎儿样本的FF比较,差异均有统计学意义(P<0.05).微缺失组真阳性和假阳性胎儿样本的FF比较,差异均有统计学意义(P<0.05);微重复组真阳性和假阳性胎儿样本的FF无显著差异.结论:孕妇血浆cffDNA水平受母体和胎儿特征共同影响.临床实践中,应根据孕妇特征和FF进行NIPS的遗传咨询.

Objective:To detect and analyze the gene variation types of 64 unrelated pedigrees affected with autosomal dominant polycystic kidney disease (ADPKD), and explore the detection efficiency of multiple gene analysis techniques and variation characteristics.Methods:It was a cross-sectional study. The clinical data of 64 pedigrees with ADPKD from Nephrology Department or Genetic and Prenatal Diagnosis Center of the First Affiliated Hospital of Zhengzhou University from December 2017 to August 2020 were retrospectively analyzed. The blood samples of probands and other family members were collected. Genetic analysis was carried out by next generation sequencing, and suspected mutations were verified by multiplex ligation-dependent probe amplification, or long-range PCR combined with Sanger sequencing. Prenatal diagnosis for high-risk fetuses was performed by fetal villi or amniotic fluid cells after genotyping without maternal genomic DNA contamination.Results:Among detected 64 pedigrees, 57 pedigrees (89.06%) had genetic variants in PKD1/PKD2. A total of 49 pathogenic/likely pathogenic variants in PKD1/PKD2 were identified in 51 pedigrees (79.69%), including 14 nonsense variants (28.57%), 14 frameshift variants (28.57%), 11 missense variants (22.45%), 5 splicing variants (10.20%) and 5 deletion variants (10.20%). Of these variants, 87.76% (43/49) were in PKD1 and 12.24% (6/49) were in PKD2. Totally, 14 novel variants in PKD1/ PKD2 were identified, including 7 frameshift variants, 3 splicing variants, 2 nonsense variants, 1 deletion variant and 1 missense variant, of which 11 variants were in PKD1 and 3 variants were in PKD2. Twenty high-risk fetuses from 17 pedigrees received prenatal diagnosis, in whom 6 fetuses had PKD1 variation, and other 14 fetuses had no PKD1/ PKD2-genetic variation. Conclusions:The combination of next-generation sequencing, multiplex ligation-dependent probe amplification, and long-range PCR combined with Sanger sequencing can be helpful for rapid, efficient and accurate genetic diagnosis of ADPKD pedigrees. Point mutations are the most common types in PKD1/PKD2. Fourteen novel variants in PKD1/PKD2 extend its pathogenic variant spectrum and can provide basis for genetic counseling and prenatal diagnosis of ADPKD pedigrees.

OBJECTIVE:To explore the cause for a twin pregnancy with false negative result for 22q11.2 deletion syndrome by expanded non-invasive prenatal testing (NIPT-plus).METHODS:A pregnant woman with twin pregnancy through in-vitro fertilization and negative result of NIPT-plus was selected as the study subject. Amniocentesis was conducted after ultrasonic finding of fetal abnormalities. In addition to conventional G-banded karyotyping, copy number variation sequencing (CNV-Seq) was used to detect chromosomal microdeletion and microduplication. Clinical data of the woman were analyzed to explore the reasons underlying the false negative result.RESULTS:NIPT-plus has yielded a negative result with 11.77 Mb unique reads and 3.05% fetal fraction. Both fetuses had a normal karyotype (46,XY and 46,XX). CNV-seq indicated that one of the fetuses was normal, whilst the other was diagnosed with a 2.58 Mb deletion in the 22q11.2 region.CONCLUSION:The false negative result may be attributed to the combined influence of low fetal fraction, high BMI, twin pregnancy through IVF and a relatively small deletion fragment. Ultrasonography exam following a low-risk result of NIPT-plus should not be neglected.

OBJECTIVE:To explore the genetic etiology for a Chinese pedigree affected with Meckel syndrome.METHODS:A pedigree with a history of three consecutive adverse pregnancies which presented at the First Affiliated Hospital of Zhengzhou University on August 31, 2017 was selected as the study subject. Clinical data of the pedigree were collected. High-throughput sequencing was carried out to screen for variants of ciliopathy-related genes in the third fetus following induced abortion, and candidate variant was verified by Sanger sequencing.RESULTS:The first pregnancy of the couple had ended as spontaneous abortion, whilst the fetus of the second pregnancy was suspected for having ciliopathy, though no genetic testing was carried out following elected abortion. The fetus of the third pregnancy was suspected for having ciliopathy, and high-throughput sequencing and Sanger sequencing had shown that the fetus had harbored compound heterozygous variants of the TMEM67 gene, including c.978+1G>A from the father and c.1288G>C (p.D430H) from the mother. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the c.978+1G>A was classified as a pathogenic variant (PVS1+PM2_Supporting+PP5), whilst the newly discovered c.1288G>C (p.D430H) was classified as a likely pathogenic variant (PM2_Supporting+PM3+PM5+PP3).CONCLUSION:The c.978+1G>A and c.1288G>C (p.D430H) compound heterozygous variants of the TMEM67 gene probably underlay the three consecutive adverse pregnancies suspected for ciliopathy in this pedigree. The discovery of c.1288G>C (p.D430H) has also expanded the mutational spectrum of the TMEM67 gene.

无创产前检测(non-invasive prenatal testing,NIPT)技术因其高灵敏度和特异度的特点已广泛应用于胎儿染色体异常的产前筛查之中.胎儿游离DNA浓度(fetal fraction,FF)是影响 NIPT结果准确性的关键因素之一.不同检测平台对 FF 的最低阈值设定不同,FF 达不到检测最低阈值是导致NIPT检测失败的重要原因之一.影响 FF的因素众多,主要可分为生物学因素和实验相关因素.低FF也与妊娠期并发症或异常妊娠有一定相关性,其后续处理需引起重视.本文将从可能引起 FF降低的因素及后续如何进行妊娠期管理等方面进行综述.

OBJECTIVE:To explore the genetic basis for a child featuring Chediak-Higashi syndrome (CHS).METHODS:Clinical manifestations and results of auxiliary examination of the proband were analyzed. The proband was subjected to whole exome sequencing, and the results were verified by Sanger sequencing. Correlation between the genotype and clinical phenotype was analyzed.RESULTS:The proband showed partial skin albinism, recurrent respiratory infection and other immune deficiencies. Genetic testing showed that he has harbored c.2437C>T (p.Arg813*) and c.6077dupA (p.Tyr2026fs) (NM_000081) compound heterozygous variants of the LYST gene, for which his parents were both carriers. Neither variant was reported previously. HEAT repeats domain was frequently associated with more severe phenotype of CHS (81.6%), whilst no variant has been found in the PH_BEACH domain.CONCLUSION:This study has enriched the spectrum of LYST gene variants associated with CHS and enabled clinical diagnosis, prenatal diagnosis and prognostic evaluation for the child.

OBJECTIVE:To explore the genetic etiology of a Chinese pedigree affected with infantile hepatitis syndrome.METHODS:Genes associated with liver diseases subjected to high-throughput sequencing. Candidate variants were validated by Sanger sequencing of the proband and his parents. The pathogenicity of the variants was analyzed through bioinformatic analysis.RESULTS:High-throughput sequencing revealed that the proband has harbored c.182T>C (p.F61S) and c.293C>T (p.P98L) variants of the MPV17 gene, which were verified by Sanger sequencing to be inherited from his parents. The variant c.182T>C (p.F61S) was unreported previously and predicted to be likely pathogenic by bioinformatic analysis.CONCLUSION:The proband was caused by the compound heterozygous variations of MPV17 gene including c.182T>C (p.F61S) and c.293C>T (p.P98L). Discovery of the novel variant has enriched the spectrum of pathogenic variants of the MPV17 gene.

OBJECTIVE:To explore the genetic basis for a patient presenting with renal insufficiency.METHODS:The patient was subjected to whole exome sequencing, and the candidate variant was verified by Sanger sequencing. Transcriptional activity of the PAX2 gene was analyzed by using a PRS4-EGFP reporter plasmid.RESULTS:Genetic testing revealed that the patient has carried a novel de novo heterozygous variant c.418C>T (p.Arg140Trp) of the PAX2 gene. The influence of c.389C>G (p.Pro130Arg), c.478G>A (p.Ala160Thr), c.418C>G (p. Arg140Gly) and c.418C>T (p.Arg140Trp) variants on the transcriptional activity was also evaluated. Functional study has illustrated that the PAX2-P130R, PAX2-R140G and PAX2-R140W variants all had a significant inhibitory effect on the transcriptional activity, but not the PAX2-A160T variant.CONCLUSION:The isolated renal hypoplasia of the proband is probably due to the likely pathogenic variant of the PAX2 gene.

Abstract Background The molecular mutations of the L1CAM gene and the imaging appearances of four fetuses with L1 syndrome from three independent Chinese families with a history of hydrocephalus were reported in this study. Two of the three are novel L1CAM variants. Methods Results of clinical and imaging examinations of three Chinese families were collected. Fetal samples were collected by puncture, genomic DNA was extracted, whole‐exome sequencing was performed, and the L1CAM gene mutation sites were verified by PCR and Sanger sequencing. Results In this case report, we described the imaging appearance and investigated the mutations of the L1CAM gene in three Chinese families with a history of L1 syndrome; these included two nonsense mutations (c.262C>T and c.261C>G) and one splice‐site mutation (c.524‐1G>A). Two of these three are novel L1CAM variants: c.262C>T and c.261C>G. The results of the sonographic images of the affected fetuses showed severe hydrocephalus. Bilateral lateral ventricles were dilated in the fetuses with c.262C>T and c.261C>G mutations. The left ventricle was about 14 mm wide and the right was about 14 mm in the fetus with c.262C>T mutation. The left ventricle was about 24.9 mm wide and the right was about 23.9 mm in the fetus with c.261C>G mutation. The ultrasound examination of the fetus with c.524‐1G>A mutation showed that the third ventricle (7.5 mm wide) was raised, and the fourth ventricle was communicated with the cisterna magna. The parents requested termination of the above pregnancy. Conclusion The current study emphasizes the importance of combining family history, prenatal ultrasonography, and L1CAM mutation testing positive for the diagnosis of the L1 syndrome.

Background The next generation sequencing (NGS) based non-invasive prenatal test (NIPT) has outplayed the traditional serum biochemical tests (SBT) in screen of fetal aneuploidies with a high sensitivity and specificity. However, it has not been widely used as a primary screen tool due to its high cost and the cheaper SBT is still the choice for primary screen even with well-known shortages in sensitivity and specificity. Here, we report a multiplex droplet digital PCR NIPT (dPCR-NIPT) assay that can detect trisomies 21, 18 and 13 (T21, T18 and T13) in a single tube reaction with a better sensitivity and specificity than the SBT and a much cheaper price than the NGS-NIPT. Methods In this study, the dPCR-NIPT assay’s non-clinical characteristics were evaluated to verify the cell free fetal DNA (cffDNA) fraction enrichment efficiencies, the target cell free DNA (cfDNA) concentration enrichment, the analytical sensitivity, and the sample quality control on the minimum concentration of cfDNA required for the assay. We validated the clinical performance for this assay by blindly testing 283 clinical maternal plasma samples, including 36 trisomic positive samples, from high risk pregnancies to access its sensitivity and specificity. The cost effectiveness of using the dPCR-NIPT assay as the primary screen tool was also analyzed and compared to that of the existing contingent strategy (CS) using the SBT as the primary screen tool and the strategy of NGS-NIPT as the first-tier screen tool in a simulating situation. Results For the non-clinical characteristics, the sample processing reagents could enrich the cffDNA fraction by around 2 folds, and the analytical sensitivity showed that the assay was able to detect trisomies at a cffDNA fraction as low as 5% and the extracted cfDNA concentration as low as 0.2 ng/μL. By testing the 283 clinical samples, the dPCR-NIPT assay demonstrated a detection sensitivity of 100% and a specificity of 95.12%. Compared to the existing CS and the NGS-NIPT as the first-tier screen strategy, dPCR-NIPT assay used as a primary screen tool followed by the NGS-NIPT rescreen is the most economical approach to screen pregnant women for fetal aneuploidies without sacrificing the positive detection rate. Conclusion This is the first report on a dPCR-NIPT assay, consisting of all the necessary reagents from sample processing to multiplex dPCR amplification, can detect T21, T18 and T13 in a single tube reaction. The study results reveal that this assay has a sensitivity and specificity superior to the SBT and a cost much lower than the NGS-NIPT. Thus, from both the test performance and the economic benefit points of views, using the dPCR-NIPT assay to replace the SBT as a primary screen tool followed by the NGS-NIPT rescreen would be a better approach than the existing CS for detection of fetal aneuploidies in maternal plasma.

OBJECTIVE:To explore the genetic etiology of a patient with mucopolysaccharidosis type II (MPSII).METHODS:The IDS gene of the proband and his mother was detected by Sanger sequencing, agarose gel electrophoresis, real-time PCR and multiple ligation-dependent probe amplification (MLPA). Prenatal diagnosis was performed on amniotic fluid sample.RESULTS:Agarose gel electrophoresis, real-time PCR, and MLPA all showed that exon 2 of IDS gene of the proband was deleted, for which his mother was normal. Prenatal diagnosis showed that the fetus was a normal male.CONCLUSION:The de novo deletion of exon 2 of the IDS gene probably underlay the MPSII in this patient. Above finding has broadened the mutation spectrum of the IDS gene. The combined methods for the detection of IDS gene mutations could make accurate prenatal diagnosis for MPSII.

Background The relatively high incidence and the clinical symptoms of sex chromosome aneuploidies (SCAs) make prenatal screening of SCAs an attractive option for pregnant women. However, limited studies have assessed the clinical performance of noninvasive prenatal testing (NIPT) for screening SCAs. This study was performed to evaluate the clinical performance of NIPT for SCAs in singleton pregnancies in central China. Methods Noninvasive prenatal testing was performed using next-generation sequencing. Standard Z-score analysis was used to identify fetal SCAs. NIPT-positive results were confirmed by invasive prenatal diagnosis (IPD). Results A total of 42,164 pregnant women with singleton pregnancies were recruited in this study. They were divided into the following five groups with different clinical indications: with ultrasound soft index abnormalities (9.23%, 3,892/42,164); with advanced maternal age (22.14%, 9,336/42,164); with high risk for maternal serum screening (MSS) (18.35%, 7,738/42,164); with an intermediate risk for MSS (26.6%, 11,215/42,164); and with low risk (23.68%, 9,983/42,164). In all, 223 women had a high risk for SCAs by NIPT with a positive rate of 0.53%. There was no significant difference associated with the five groups in the positive rate. Of all of the positive results, 89 were 45,X (39.91%), 38 were 47,XXX (17.04%), 31 were 46,XY,del(X) (13.90%), 50 were 47,XXY (22.42%,), and 15 were 47,XYY (6.73%). Finally, 147 participants (65.92%) chose to undergo IPD, and 47 cases were confirmed. The combined positive predictive value (PPV) of NIPT for SCA was 31.97% (47/147). PPV was high for 47,XYY (100%, 11/11), moderate for 47,XXX (42.86%, 9/21) and 47,XXY (45.45%, 15/33), but low for 45,X (16.13%, 10/62) and 46,XY,del(X) (10%, 2/20). The termination rates of Turner syndrome and 47,XXY syndrome were higher than 47,XXX and 47,XYY syndromes. Conclusion In this relatively large cohort, we evaluated the value of NIPT for SCAs. Our data showed that with informed consent and subsequent professional genetical consulting, NIPT can be a useful method to screen SCAs.

OBJECTIVE:To explore the clinical characteristics and molecular pathogenesis of a child with autosomal dominant polycystic kidney disease (ARPKD).METHODS:Prenatal ultrasound, clinical feature and family history of the child were analyzed. Whole exome sequencing was carried out for the child. Candidate variants were verified by Sanger sequencing.RESULTS:The child has featured premature birth with very low weight, neonatal respiratory distress, metabolic acidosis, and congenital nephrotic syndrome. Gene sequencing revealed that he has harbored compound heterozygous variants of the PKHD1 gene (NM_138694), including c.3885T>A (p.Tyr1295*) in exon 32 and c.7812_7816dupTGATA (p.Thr2606Metfs*63) in exon 49, which were respectively inherited from his mother and father.CONCLUSION:The compound heterozygous variants of the PKHD1 gene probably underlay the disease in this child.

OBJECTIVE:To explore the genetic etiology of a child with suspected propionic acidemia.METHODS:Genomic DNA was extracted from peripheral blood sample of the child and subjected to high-throughput sequencing to screen pathogenic variants of genes associated with methylmalonic acidemia and propionic acidemia, including MUT, MMACHC, MMAA, MMAB, MMADHC, LMBRD1, PCCA, PCCB and SLC22A5. Candidate variants were verified by Sanger sequencing of the proband, her parents and sister.RESULTS:The proband was found to harbor two pathogenic variants of the MUT gene, namely c.1560+2T>C and c.729_730insTT (p.Asp244fs), but not in genes associated with propionic acidemia. Her sister and father had carried c.1560+2T>C, and her mother had carried c.729_730insTT (p.Asp244fs).CONCLUSION:The proband was diagnosed as methylmalonic acidemia due to compound heterozygous variants of c.1560+2T>C and c.729_730insTT (p.Asp244fs) of the MUT gene. Her elder sister and parents were all carriers. Genetic testing has facilitated differential diagnosis of methylmalonic acidemia and propionic acidemia in this pedigree.