Figure 1.
A missense mutation in the DNMT1 gene ameliorates HbE/β-thalassemia. (A) Two respective cohorts, including 7968 individuals from southern China in the ChinaMap project (www.mbiobank.com) and a previously established cohort of 1142 southern Chinese β-thalassemia patients, were screened for the S878F mutation. The frequency and number of the S878F mutant allele in each cohort are shown. (B) Verification of the novel DNMT1 mutation and its correlation with HbF levels for 2 Chinese pedigrees. Representative Sanger sequencing chromatograms from 4 subjects are shown on the bottom, identifying a heterozygous DNMT1 missense mutation (c.2633G>A, p.Ser878Phe) in the probands of the 2 families. The genotypes of HBB gene mutations, DNMT1 mutation, and HbF levels (grams per deciliter) are indicated for each family member tested. Three positive cases with this mutation screened by a patient-based NGS approach are marked by red stars. (C) Conserved sequence analysis of the S878F mutation across vertebrate species. The structure of the protein encoded by DNMT1 is shown on the top. The S878F missense mutation (marked with a red star) occurred in the BAH1 domain, within the N-terminal regulatory domain. Below are enlarged graphs depicting a partial sequence alignment of the BAH1 domain around the position of this mutation, indicating a highly conserved amino acid sequence (shaded in light blue). (D) Left, prediction of hydrogen bond networks (broken black lines) formed by Ser878 (blue), Gln1293 (red), and Pro1320 (yellow) in WT DNMT1. Right, loss of hydrogen bonds in the S878F mutation DNMT1. The BAH1 domain is shaded in gold and the C-terminal catalytic domain is shaded in green. The image was generated using PyMOL (http://www.pymol.org/). (E-F) The effects of the S878F mutation on the levels of HbF (E) and age at onset of anemia (F) in individuals with HbE/β-thalassemia. Selected individuals had the same globin genotype category (HbE/β0 and αα/αα) and similar HbF-modulating genetic variants (KLF1WT/WT, rs368698783[GG], rs4671393 [GG or GA], or rs9399137 [TT or CT]). The data were obtained from a comparison of 3 cases with a DNMT1 mutation to 63 samples without this mutation in the control group, from a cohort of patients with 1142 β-thalassemia. Graphs depict the mutated group (blue column) and WT group (brown column), presented as the means ± standard error of the mean (SEM) (****P ≤ .0001; ***P ≤ .001). (G) Kaplan-Meier survival curves for the comparison of well-matched HbE/β0-thalassemia cases with or without the DNMT1 mutation. The sample-matched pair, 3 vs 63 patient cases with or without the S878F mutation are shown at the top of the chart. The 2 colored lines represent the 2 groups. Selection of samples is described in supplemental Tables 1 and 8. We used the log-rank test to compare the median age at first transfusion between the 2 groups (P = .027). DAF, derived allele frequency; PDB, Protein Data Bank.

A missense mutation in the DNMT1 gene ameliorates HbE/β-thalassemia. (A) Two respective cohorts, including 7968 individuals from southern China in the ChinaMap project (www.mbiobank.com) and a previously established cohort of 1142 southern Chinese β-thalassemia patients, were screened for the S878F mutation. The frequency and number of the S878F mutant allele in each cohort are shown. (B) Verification of the novel DNMT1 mutation and its correlation with HbF levels for 2 Chinese pedigrees. Representative Sanger sequencing chromatograms from 4 subjects are shown on the bottom, identifying a heterozygous DNMT1 missense mutation (c.2633G>A, p.Ser878Phe) in the probands of the 2 families. The genotypes of HBB gene mutations, DNMT1 mutation, and HbF levels (grams per deciliter) are indicated for each family member tested. Three positive cases with this mutation screened by a patient-based NGS approach are marked by red stars. (C) Conserved sequence analysis of the S878F mutation across vertebrate species. The structure of the protein encoded by DNMT1 is shown on the top. The S878F missense mutation (marked with a red star) occurred in the BAH1 domain, within the N-terminal regulatory domain. Below are enlarged graphs depicting a partial sequence alignment of the BAH1 domain around the position of this mutation, indicating a highly conserved amino acid sequence (shaded in light blue). (D) Left, prediction of hydrogen bond networks (broken black lines) formed by Ser878 (blue), Gln1293 (red), and Pro1320 (yellow) in WT DNMT1. Right, loss of hydrogen bonds in the S878F mutation DNMT1. The BAH1 domain is shaded in gold and the C-terminal catalytic domain is shaded in green. The image was generated using PyMOL (http://www.pymol.org/). (E-F) The effects of the S878F mutation on the levels of HbF (E) and age at onset of anemia (F) in individuals with HbE/β-thalassemia. Selected individuals had the same globin genotype category (HbE/β0 and αα/αα) and similar HbF-modulating genetic variants (KLF1WT/WT, rs368698783[GG], rs4671393 [GG or GA], or rs9399137 [TT or CT]). The data were obtained from a comparison of 3 cases with a DNMT1 mutation to 63 samples without this mutation in the control group, from a cohort of patients with 1142 β-thalassemia. Graphs depict the mutated group (blue column) and WT group (brown column), presented as the means ± standard error of the mean (SEM) (****P ≤ .0001; ***P ≤ .001). (G) Kaplan-Meier survival curves for the comparison of well-matched HbE/β0-thalassemia cases with or without the DNMT1 mutation. The sample-matched pair, 3 vs 63 patient cases with or without the S878F mutation are shown at the top of the chart. The 2 colored lines represent the 2 groups. Selection of samples is described in supplemental Tables 1 and 8. We used the log-rank test to compare the median age at first transfusion between the 2 groups (P = .027). DAF, derived allele frequency; PDB, Protein Data Bank.

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