A natural DNMT1 mutation elevates the fetal hemoglobin level via epigenetic derepression of the γ-globin gene in ß-thalassemia.

DNA methyltransferase 1 (DNMT1) is a major epigenetic regulator of the formation of large macromolecular complexes that repress human γ-globin expression by maintaining DNA methylation. However, very little is known about the association of DNMT1 variants with ß-thalassemia phenotypes. We systematically investigated associations between variants in DNMT1 and phenotypes in 1142 ß-thalassemia subjects and identified a novel missense mutation (c.2633G>A, S878F) in the DNMT1 bromo-adjacent homology-1 (BAH1) domain. We functionally characterized this mutation in CD34+ cells from patients and engineered HuDEP-2 mutant cells. Our results demonstrate that DNMT1 phosphorylation is abrogated by substituting serine with phenylalanine at position 878, resulting in lower stability and catalytic activity loss. S878F mutation also attenuated DNMT1 interactions with BCL11A, GATA1, and HDAC1/2, and reduced recruitment of DNMT1 to the γ-globin (HBG) promoters, leading to epigenetic derepression of γ-globin expression. By analyzing the F-cell pattern, we demonstrated that the effect of DNMT1 mutation on increased fetal hemoglobin (HbF) is heterocellular. Furthermore, introduction of S878F mutation into erythroid cells by clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) recapitulated γ-globin reactivation. Thus, the natural S878F DNMT1 mutation is a novel modulator of HbF synthesis and represents a potential new therapeutic target for ß-hemoglobinopathies.

MALDI-TOF-MS for Rapid Screening and Typing of ß-Globin Variant and ß-Thalassemia through Direct Measurements of Intact Globin Chains.

BACKGROUND: Traditional phenotype-based screening for ß-globin variant and ß-thalassemia using hematological parameters is time-consuming with low-resolution detection. Development of a MALDI-TOF-MS assay using alternative markers is needed. METHODS: We constructed a MALDI-TOF-MS-based approach for identifying various ß-globin disorders and classifying thalassemia major (TM) and thalassemia intermedia (TI) patients using 901 training samples with known HBB/HBA genotypes. We then validated the accuracy of population screening and clinical classification in 2 separate cohorts consisting of 16 172 participants and 201 ß-thalassemia patients. Traditional methods were used as controls. Genetic tests were considered the gold standard for testing positive specimens. RESULTS: We established a prediction model for identifying different forms of ß-globin disorders in a single MALDI-TOF-MS test based on δ- to ß-globin, γ- to α-globin, γ- to ß-globin ratios, and/or the abnormal globin-chain patterns. Our validation study yielded comparable results of clinical specificity (99.89% vs 99.71%), and accuracy (99.78% vs 99.16%) between the new assay and traditional methods but higher clinical sensitivity for the new method (97.52% vs 88.01%). The new assay identified 22 additional abnormal hemoglobins in 69 individuals including 9 novel ones, and accurately screened for 9 carriers of deletional hereditary persistence of fetal hemoglobin or δß-thalassemia. TM and TI were well classified in 178 samples out of 201 ß-thalassemia patients. CONCLUSIONS: MALDI-TOF-MS is a highly accurate, predictive tool that could be suitable for large-scale screening and clinical classification of ß-globin disorders.

The value of single-molecule real-time technology in the diagnosis of rare thalassemia variants and analysis of phenotype-genotype correlation.

To compare single-molecule real-time technology (SMRT) and conventional genetic diagnostic technology of rare types of thalassemia mutations, and to analyze the molecular characteristics and phenotypes of rare thalassemia gene variants, we used 434 cases with positive hematology screening as the cohort, then used SMRT technology and conventional gene diagnosis technology [(Gap-PCR, multiple ligation probe amplification technology (MLPA), PCR-reverse dot blot (RDB)] for thalassemia gene screening. Among the 434 enrolled cases, conventional technology identified 318 patients with variants (73.27%) and 116 patients without variants (26.73%), SMRT identified 361 patients with variants (83.18%), and 73 patients without variants (16.82%). The positive detection rate of SMRT was 9.91% higher than conventional technology. Combination of the two methods identified 485 positive alleles among 49 types of variant. The genotypes of 354 cases were concordant between the two methods, while 80 cases were discordant. Among the 80 cases, 76 cases had variants only identified in SMRT method, 3 cases had variants only identified in conventional method, and 1 false positive result by the traditional PCR detection technology. Except the three variants in HS40 and HBG1-HBG2 loci, which was beyond the design of SMRT method in this study, all the other discordant variants identified by SMRT were validated by further Sanger sequencing or MLPA. The hematological phenotypic parameters of 80 discordant cases were also analyzed. SMRT technology increased the positive detection rate of thalassemia genes, and detected rare thalassemia cases with variable phenotypes, which had great significance for clinical thalassemia gene screening.

Characterization of two novel Alu element-mediated α-globin gene cluster deletions causing α0-thalassemia by targeted next-generation sequencing.

α-thalassemia is an inherited blood disorder commonly caused by deletions or point mutations involving one or both α-globin genes. Recent studies shed new light on the critical role of upstream enhancers multi-species conserved sequences (MCSs) in the ordered regulation of α-globin gene expression. Herein, we reported two unrelated probands with deletions in α-globin genes and MCSs, respectively. The proband from Family A is a compound heterozygote carrying a known α+ mutation (-α3.7) and a novel 60.2 kb deletion causing the absence of both α-globin genes. The proband from Family B, on the other hand, is a compound heterozygote with a known α0 mutation (--SEA) and a novel deletion involving only upstream regulatory elements MCS-R1, R2 and R3, while the α-globin genes remain intact. Notably, both these two patients suffered varied extent of anemia, indicating that the loss of enhancer elements could equally lead to reduced synthesis of α-globin. Upon these observations, we then confirmed the exact breakpoints of these two novel deletions using a targeted next-generation sequencing (NGS) previously established by our group, which may enable further elucidation of the rearrangement mechanisms on these deletions and functional dissection of MCSs. Taken together, our study reports a reliable NGS-based molecular screening approach for accurate identification of copy number variations (CNVs) in the α-globin cluster and the genetic diagnosis of these two probands may help to extend the spectrum of α-thalassemia mutations in Chinese population.

Application of Copy Number Variation Sequencing in Genetic Analysis of Miscarriages in Early and Middle Pregnancy.

High-throughput sequencing based on copy number variation (CNV-seq) is commonly used to detect chromosomal abnormalities. This study identifies chromosomal abnormalities in aborted embryos/fetuses in early and middle pregnancy and explores the application value of CNV-seq in determining the causes of pregnancy termination. High-throughput sequencing was used to detect chromosome copy number variations (CNVs) in 116 aborted embryos in early and middle pregnancy. The detection data were compared with the Database of Genomic Variants (DGV), the Database of Chromosomal Imbalance and Phenotype in Humans using Ensemble Resources (DECIPHER), and the Online Mendelian Inheritance in Man (OMIM) database to determine the CNV type and the clinical significance. High-throughput sequencing results were successfully obtained in 109 out of 116 specimens, with a detection success rate of 93.97%. In brief, there were 64 cases with abnormal chromosome numbers and 23 cases with CNVs, in which 10 were pathogenic mutations and 13 were variants of uncertain significance. An abnormal chromosome number is the most important reason for embryo termination in early and middle pregnancy, followed by pathogenic chromosome CNVs. CNV-seq can quickly and accurately detect chromosome abnormalities and identify microdeletion and microduplication CNVs that cannot be detected by conventional chromosome analysis, which is convenient and efficient for genetic etiology diagnosis in miscarriage.

Diagnosis and Prenatal Diagnosis in a Chinese Family Carrying the Rare α-Thalassemia Gene HBA2: c.1A>G Mutation.

The aim of this study was to identify the rare thalassemia genotype in a family and perform prenatal diagnosis (PND) on the proband's unborn child. Peripheral blood was collected from the family members for hematology analysis and capillary electrophoresis (CE) analysis. Peripheral blood and cord blood were analyzed by gap-polymerase chain reaction (gap-PCR), reverse dot-blot and Sanger sequencing for genotypes of α-thalassemia (α-thal). A heterozygous mutation, HBA2: c.1A>G, was identified in the proband and his father. Two compound heterozygous variants, HBA2: c.1A>G and the - -SEA (Southeast Asian) deletion, were revealed in the proband's unborn child. The hemoglobin (Hb) CE result of the fetal cord blood indicated the fetus had Hb H disease. We have identified a rare thalassemia mutation (HBA2: c.1A>G) in a Chinese family and enriched the rare α-thal gene pool in the Chinese population. When the patient's phenotype does not match the genotype detected by thalassemia gene detection kits, further investigation of rare genotypes should be conducted to avoid missed diagnosis or misdiagnosis, which can help guide clinical diagnosis, population screening and genetic counseling.

Pedigree Analysis of Nonhomologous Sequence Recombination of HBA1 and HBA2 Genes.

The aim of this study was to investigate a family with nonhomologous sequence recombination of HBA1 and HBA2 genes and provide a favorable basis for genetic counseling and eugenics. Peripheral blood of family members was collected. Hematological parameters were determined by an automated cell counter and hemoglobin (Hb) analysis was performed using high performance liquid chromatography (HPLC). Villus samples were taken for prenatal diagnosis (PND). Gap-polymerase chain reaction (gap-PCR) and reverse dot-blot were used for thalassemia genotyping. DNA sequencing was used to analyze the gene sequence of HBA1 (α1-globin) and HBA2 (α2-globin). The nonhomologous sequence recombination allelic variant of HBA1 and HBA2 genes were identified, namely, a gene conversion on the HBA2 gene called α12 (HBA12). The α12 allele consists primarily of the HBA2 gene sequence except for a segment of the IVS-II in which HBA2-specific sequences have been replaced by HBA1-specific sequences. The following genotypes were observed: - -SEA/αα12 (Southeast Asian deletion), αα/αα12 and αQSα/αα12 (Hb Quong Sze or Hb QS; HBA2: c.377T>C), and all manifested as small cell hypochromic anemia. To find the α12 allele in the Chinese population and clarify the influence of the α12 allele and its common inheritance with abnormal Hb and α-thalassemia (α-thal) on α-globin gene expression can help guide clinical diagnosis and genetic counseling.

[Analysis of PLA2G6 gene variant in a family affected with infantile neuroaxonal dystrophy].

OBJECTIVE: To identify potential variant in a child diagnosed as infantile neuroaxonal dystrophy. METHODS: Genomic DNA was extracted from peripheral blood samples from the patient and his parents and subjected to next generation sequencing. Suspected variant was verified by PCR and Sanger sequencing. Pathogenicity of the mutation was predicted by using bioinformatic software including SIFT and PolyPhen-2. RESULTS: The child was found to carry compound heterozygous variations c.668C>A (p.Pro223Gln) and c.2266C>T (p.Gln756Ter) of the PLA2G6 gene, which were respectively inherited from his father and mother. c.2266C>T has changed codon 756 (glutamine) into a stop codon, resulting premature termination of peptide chain synthesis. c.2266C>T has not been reported previously and was predicted to be harmful. CONCLUSION: The compound variants of c.668C>A (p.Pro223Gln) and c.2266C>T (p.Gln756Ter) of the PLA2G6 gene probably underlies the disease in the child. Above finding has enriched the variant spectrum of the PLA2G6 gene.

Copy number variations in the GATA4, NKX2-5, TBX5, BMP4 CRELD1, and 22q11.2 gene regions in Chinese children with sporadic congenital heart disease.

BACKGROUND: Congenital heart disease (CHD) is a common birth defect originating from both environmental and genetic factors. An overabundance of copy number variations (CNVs) affecting cardiac-related genes has previously been detected in individuals with CHD. OBJECTIVE: To evaluate if the presence of CNVs in the 22q11.2 region, and to determine whether GATA4, NKX2-5, TBX5, BMP, and CRELD1 genes contributed toward the pathogenesis of isolated incidences of CHDs in southwest China. METHODS: In total 167 patients from southwest China with sporadic CHD were studied, including 121 patients with ventricular septal defect (VSD), 24 with atrial septal defect (ASD), 12 with tetralogy of fallot (TOF), six VSD cases with TOF, two cases with patent ductus arteriosus (PDA), and two VSD cases with ASD. 22q11.2, GATA4, NKX2-5, TBX5, BMP4, and CRELD1 regions were screened using MLPA and copy number variation sequencing (CNV-Seq). RESULTS: A 2.5-2.8 Mb deletion in the 22q11.2 region was identified in 5 patients with CHD. Two of these patients were diagnosed with VSD, while two had VSD and ASD, and the other had TOF. 5 patients correspond to the same classical DiGeorge syndrome. A 0.86 Mb duplication in the 22q11.2 region was identified in a PDA patient, whom was without extracardiac symptoms. CONCLUSION: These data suggest that copy number variation in the 22q11.2 region is common in CHD patients in southwest China. Regardless of the presence or absence of extracardiac symptoms, results also indicate that it is necessary to perform prenatal screening for CHD.

[Analysis of CGDH gene variants and clinical features in three patients with glutaric aciduria type â ].

OBJECTIVE: To screen for potential variants of GCDH gene in 3 patients clinically diagnosed as glutaric aciduria type Ⅰ. METHODS: GCDH gene variants was detected by Sanger sequencing among the three children and their family members. RESULTS: Sanger sequencing showed that patient 1 carried compound heterozygosity variants of c.532G>A (p.Gly178Arg) and c.655G>A (p.Ala219Thr) of the GCDH gene, while his father and mother respectively carried heterozygous c.532G>A(p.Gly178Arg) and c.655G>A (p.Ala219Thr) variants. Patient 2 carried c.532G>A (p.Gly178Arg) and a novel c.1060G>T (p.Gly354Cys) compound heterozygous variant, while his father and mother respectively carried heterozygous c.532G>A (p.Gly178Arg) and c.1060G>T (p.Gly354Cys) variant. Patient 3 carried homozygous c.532G>A (p.Gly178Arg) variant of the GCDH gene, for which both of his parents were heterozygous carriers. CONCLUSION: The GCDH gene variant probably underlie the glutaric aciduria type Ⅰ among the 3 patients. Identifcation of the novel variant has enriched the spectrum of GCDH gene variants.

[Analysis of TRPM6 gene variant in a pedigree affected with hypocalcemia secondary to hypomagnesemia].

OBJECTIVE: To explore the molecular pathogenesis for a pedigree affected with hypocalcemia secondary to hypomagnesemia. METHODS: Sanger sequencing was used to detect potential variant of the TRPM6 gene in the patient and their parents. RESULTS: The results showed that the patient has carried novel homozygous c.3311C>T (p.Pro1104Leu) variant of the TRMP6 gene, for which both of his parents were heterozygous carriers. Analysis of protein functions using software predicted high risk of pathogenicity. CONCLUSION: The homozygous c.3311C>T (p.Pro1104Leu) variant of the TRPM6 gene probably underlies the disease in this patient.

[Tandem mass spectrometry analysis and genetic diagnosis of neonates with fatty acid oxidation disorders in central and northern regions of Guangxi].

OBJECTIVE: To determine the incidence and mutational types of fatty acid oxidation disorders (FAOD) in central-northern region of Guangxi. METHODS: A total of 62 953 neonates were screened for FAOD during December 2012 and December 2017. Acyl-carnitine profiling of neonatal blood sample was performed by tandem mass spectrometry using dry blood spots on a filter paper. The diagnosis of FAOD was confirmed by organic acid profiling of urea and genetic testing. RESULTS: Eighteen cases of FAOD were diagnosed among the 62 953 neonates. Among these, primary carnitine deficiency (PCD) was the most common type (n=13), which was followed by short-chain acyl-CoA dehydrogenase deficiency (SCADD) (n=2), medium-chain acyl-CoA dehydrogenase deficiency (MCADD) (n=1), multiple acyl-CoA dehydrogenase deficiency (MADD) (n=1), and carnitine palmitoyltransferase II deficiency (CPT II D) (n=1). Genetic testing has revealed two previously unreported variants, i.e., c.337G to A (p.Gly113Arg) of ACADS gene and c.737G TO T (p.Gly246Val) of ETFA gene. CONCLUSION: PCD is the most common FAOD in central-northern Guangxi. Tandem mass spectrometry combined with genetic testing may facilitate early diagnosis of FAOD.

[SLC22A5 gene mutation analysis and prenatal diagnosis for a family with primary carnitine deficiency].

OBJECTIVE: To carry out mutation analysis and prenatal diagnosis for a family affected with primary carnitine deficiency. METHODS: Genomic DNA of the proband was extracted from peripheral blood sample 10 days after birth. The 10 exons and intron/exon boundaries of the SLC22A5 gene were subjected to PCR amplification and Sanger sequencing. The proband's mother was pregnant again two years after his birth. Fetal DNA was extracted from amniocytes and subjected to PCR and Sanger sequencing. RESULTS: Tandem mass spectrometric analysis of the proband revealed low level of plasma-free carnitine whilst organic acids in urine was normal. Compound heterozygous SLC22A5 mutations c.1195C>T (inherited from his father) and c.517delC (inherited from his mother) were detected in the proband. Prenatal diagnosis has detected no mutation in the fetus. The plasma-free carnitine was normal after birth. CONCLUSION: Appropriate genetic testing and prenatal diagnosis can prevent further child with carnitine deficiency. The identification of c.517delC, a novel mutation, enriched the spectrum of SLC22A5 mutations.

[Clinical and genetic analysis of a child with Noonan syndrome].

OBJECTIVE: To identify potential mutation in a child clinically diagnosed as Noonan syndrome and to provide genetic counseling and prenatal diagnosis for his family. METHODS: Genomic DNA was extracted from peripheral blood samples of the patient and his parents, and amniotic fluid was taken from the mother during the second trimester. Next generation sequencing (NGS) was used to screen potential mutations from genomic DNA. Suspected mutation was verified by Sanger sequencing. RESULTS: A heterozygous c.4A>G (p.Ser2Gly) mutation of the SHOC2 gene was identified in the patient but not among other family members including the fetus. CONCLUSION: The Noonan syndrome is probably caused by the c.4A>G mutation of the SHOC2 gene. NGS is helpful for the diagnosis of complicated genetic diseases. SHOC2 gene mutation screening is recommended for patient suspected for Noonan syndrome.

[Analysis of P gene variations among fourteen patients with oculocutaneous albinism type II].

OBJECTIVE: To analyze variations of TYR and P genes among 14 patients with clinically diagnosed oculocutaneous albinism. METHODS: Potential variations of the TYR and P genes were detected by Sanger sequencing. Novel variations were predicted with bioinformatics software including SIFT and PolyPhen-2. RESULTS: No variation was found in the TYR gene, while 9 types of variations were found in the P gene among the 14 patients, which included c.803-3C>G (7/26), c.1327G>A (p.Val443Ile) (5/26), c.632C>T (p.Pro211Leu) (4/26), c.1832T>C (p.Leu611Pro) (3/26), c.1349C>A (p.Thr450Lys) (2/26), c.2363C>T (p.Ser788Leu) (2/26), c.2228C>T (p.Pro743Leu) (1/26), c.1525A>G (p.Thr509Ala) (1/26), and c.1349C>T (p.Thr450Met) (1/26). Only 1 heterozygous variation was detected in 2 families. c.2363C>T (p.Ser788Leu), c.1832T>C (p.Leu611Pro) and c.1525A>G (p.Thr509Ala) were not reported previously and predicted as "harmful" to the protein function. CONCLUSION: The main type of ocular albinism is oculocutaneous albinism type II in Liuzhou region, where the most common variations of the P gene were c.803-3C>G and c.1327G>A (p.Val443Ile). Above finding has enriched the variation spectrum of the P gene.

Systematic assessment of the performance of whole-genome amplification for SNP/CNV detection and ß-thalassemia genotyping.

In this study, we aimed to assess the performance of two whole-genome amplification methods, multiple displacement amplification (MDA), and multiple annealing and looping-based amplification cycle (MALBAC), for ß-thalassemia genotyping and single-nucleotide polymorphism (SNP)/copy-number variant (CNV) detection using two DNA sequencing assays. We collected peripheral blood, cell lines, and discarded embryos, and carried out MALBAC and MDA on single-cell and five-cell samples. We detected and statistically analyzed differences in the amplification efficiency, positive predictive value, sensitivity, allele dropout (ADO) rate, SNPs, and CV values between the two methods. Through Sanger sequencing at the single-cell and five-cell levels, we showed that both the amplification rate and ADO rate of MDA were better than those using MALBAC, and the sensitivity and positive predictive value obtained from MDA were higher than those from MALBAC for ß-thalassemia genotyping. Using next-generation sequencing (NGS) at the single-cell level, we confirmed that MDA has better properties than MALBAC for SNP detection. However, MALBAC was more stable and homogeneous than MDA using low-depth NGS at the single-cell level for CNV detection. We conclude that MALBAC is the better option for CNV detection, while MDA is better suited for SNV detection.

[Clinical and cytogenetic study in a child with de novo chromosome 9 abnormality].

This study aimed to analyze the clinical phenotype of chromosome 9p deletion or duplication and its relationship with karyotype. A patient, female, aged 6 months, visited the hospital due to motor developmental delay. Karyotype analysis identified abnormalities of chromosome 9 short arm, and high-throughput sequencing found 9p24.3-9p23 deletion and 9p23-9p13.1 duplication. Her parents had a normal karyotype. Karyotype analysis combined with high-throughput sequencing is of great significance for improving the efficiency of etiological diagnosis in children with motor developmental delay or multiple congenital deformities and mental retardation.

Evaluation and comparison of three assays for molecular detection of spinal muscular atrophy.

BACKGROUND: Spinal muscular atrophy (SMA) is mainly caused by deletions in SMA-related genes. The objective of this study was to develop gene-dosage assays for diagnosing SMA. METHODS: A multiplex, quantitative PCR assay and a CNVplex assay were developed for determining the copy number of SMN1, SMN2, and NAIP. Reproducibility and specificity of the two assays were compared to a multiple ligation-dependent probe amplification (MLPA) assay. To evaluate reproducibility, 30 samples were analyzed three times using the three assays. A total of 317 samples were used to assess the specificity of the two assays. RESULTS: The multiplex quantitative PCR (qPCR) assay had higher reproducibility. Intra-assay CVs were 3.01%-8.52% and inter-assay CVs were 4.12%-6.24%. The CNVplex assay had ratios that were closer to expected (0.49-0.5 for one copy, 1.03-1.0 for two copies, and 1.50-1.50 for three copies). Diagnostic accuracy rates for the two assays were 100%. CONCLUSIONS: The multiplex qPCR assay was a simple, rapid, and cost-effective method for routine SMA diagnosis and carrier screening. The CNVplex assay could be used to detect SMAs with complicated gene structures. The assays were reliable and could be used as alternative methods for clinical diagnosis of SMA.

[Genetic diagnosis of 10 neonates with primary carnitine deficiency].

OBJECTIVE: To study the gene mutation profile of primary carnitine deficiency (PCD) in neonates, and to provide a theoretical basis for early diagnosis and treatment, genetic counseling, and prenatal diagnosis of PCD. METHODS: Acylcarnitine profile analysis was performed by tandem mass spectrometry using 34 167 dry blood spots on filter paper. The SLC22A5 gene was sequenced and analyzed in neonates with free carnitine (C0) levels lower than 10 µmol/L as well as their parents. RESULTS: In the acylcarnitine profile analysis, a C0 level lower than 10 µmol/L was found in 10 neonates, but C0 level was not reduced in their mothers. The 10 neonates had 10 types of mutations at 20 different sites in the SLC22A5 gene, which included 4 previously unreported mutations: c.976C>T, c.919delG, c.517delC, and c.338G>A. Bioinformatics analysis showed that the four new mutations were associated with a risk of high pathogenicity. CONCLUSIONS: Tandem mass spectrometry combined with SLC22A5 gene sequencing may be useful for the early diagnosis of PCD. Identification of new mutations enriches the SLC22A5 gene mutation profile.