Differential HMG-CoA lyase expression in human tissues provides clues about 3-hydroxy-3-methylglutaric aciduria

3-Hydroxy-3-methylglutaric aciduria is a rare human autosomal recessive disorder caused by deficiency of 3-hydroxy-3-methylglutaryl CoA lyase (HL). This mitochondrial enzyme catalyzes the common final step of leucine degradation and ketogenesis. Acute symptoms include vomiting, seizures and lethargy, accompanied by metabolic acidosis and hypoketotic hypoglycaemia. Such organs as the liver, brain, pancreas, and heart can also be involved. However, the pathophysiology of this disease is only partially understood. We measured mRNA levels, protein expression and enzyme activity of human HMG-CoA lyase from liver, kidney, pancreas, testis, heart, skeletal muscle, and brain. Surprisingly, the pancreas is, after the liver, the tissue with most HL activity. However, in heart and adult brain, HL activity was not detected in the mitochondrial fraction. These findings contribute to our understanding of the enzyme function and the consequences of its deficiency and suggest the need for assessment of pancreatic damage in these patients.     

A single-residue mutation, G203E, causes 3-hydroxy-3-methylglutaric aciduria by occluding the substrate channel in the 3D structural model of HMG-CoA lyase

Summary 3-Hydroxy-3-methylglutaric aciduria is a rare autosomal recessive genetic disorder that affects ketogenesis and leucine metabolism. The disease is caused by mutations in the gene coding for 3-hydroxy-3-methylglutaryl-coenzyme A lyase (HL). To date 26 different mutations have been described. A (βα)₈ TIM barrel structure has been proposed for the protein, and almost all missense mutations identified so far localize in the beta sheets that define the inside cavity. We report an Italian patient who bears homozygously a novel HL mutation, c.608G > A (p. G203E) in beta sheet six. A structural model of the mutated protein suggests that glutamic acid 203 impedes catalysis by blocking the entrance to the inner cavity of the enzyme. Loss of functionality has been confirmed in expression studies in E. coli, which demonstrate that the G203E mutation completely abolishes enzyme activity. Beta sheet six and beta sheet two are the two protein regions that accumulate most missense mutations, indicating their importance in enzyme functionality. A model for the mechanism of enzyme function is proposed. Communicating editor: Michael Gibson Competing interests: None declared     

Molecular analyses of the HGO gene mutations in Turkish alkaptonuria patients suggest that the R58fs mutation originated from central Asia and was spread throughout Europe and Anatolia by human migrations

Summary: Alkaptonuria (AKU) is a rare metabolic disorder of phenylalanine catabolism that is inherited as an autosomal recessive trait. AKU is caused by loss-of-function mutations in the homogentisate 1,2-dioxygenase (HGO) gene. The deficiency of homogentisate 1,2-dioxygenase activity causes homogentisic aciduria, ochronosis and arthritis. We present the first molecular study of the HGO gene in Turkish AKU patients. Seven unrelated AKU families from different regions in Turkey were analysed. Patients in three families were homozygous for the R58fs mutation; another three families were homozygous for the R225H mutation; and one family was homozygous for the G270R mutation. Analysis of nine intragenic HGO polymorphisms showed that the R58fs, R225H and G270R Turkish AKU mutations are associated with specific HGO haplotypes. The comparison with previously reported haplotypes associated with these mutations from other populations revealed that the R225H is a recurrent mutation in Turkey, whereas G270R most likely has a Slovak origin. Most interestingly, these analyses showed that the Turkish R58fs mutation shares an HGO haplotype with the R58fs mutation found in Finland, Slovakia and India, suggesting that R58fs is an old AKU mutation that probably originated in central Asia and spread throughout Europe and Anatolia during human migrations.     

Inhibitory effect of simvastatin on the proliferation of human myeloid leukaemia cells in severe combined immunodeficient (SCID) mice

SCID mice were inoculated intravenously with cells from the human HL60 myeloblastic leukaemia cell line and then treated with the 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitor, simvastatin, by subcutaneous continuous infusion. The effect of the drug was measured by subsequent colony formation of surviving HL60 cells in vitro and flow cytometry. The number of clonogenic HL60 cells was reduced in the bone marrow of mice that received simvastatin compared with control mice by 65% and 68% in two separate experiments. The number of clonogenic, normal, murine, bone marrow progenitor cells concomitantly exposed to simvastatin in vivo , was not affected in either experiment. Flow cytometric analysis of bone marrow and spleen cells confirmed these results by showing that simvastatin had reduced the percentage of human leukaemia cells in these tissues by 70% and 88% respectively.   The data show that the reported selective effect of simvastatin against acute myeloid leukaemia cells in vitro, can be extended to this in vivo model. HL60 bears an N-ras mutation. In further in vitro studies, ketoconazole, an inhibitor of cholesterol biosynthesis post farnesyl pyrophosphate synthesis, had a similar effect to simvastatin on HL60 colony development. Furthermore, the clonogenicity of a population of N-ras mutated, primary acute myeloid leukaemia (AML) cells was no more sensitive to simvastatin than a population without the mutation. The data suggest that the inhibition of AML cell proliferation by simvastatin may be independent of the RAS signalling pathway.     

Three new novel point mutations localized within and downstream of high-mobility group-box region in SRY gene in three Indian females with Turner syndrome

Point mutations and deletions in the SRY gene result in XY sex reversal in pure gonadal dysgenesis. To date, a majority of these affect the high-mobility group (HMG) domain of SRY, which plays a key role in its DNA binding activity. We carried out molecular genetics studies in three Turner syndrome patients all presenting with 45,X/46,XY mosaic karyotype. Case 1 demonstrated an insertion of T (thymine) within helix I of HMG box leading to frame shift mutation (N82X). In case 2, insertion of A (adenine) downstream of HMG box resulted in a nonsense frame shift mutation (L159fsX167). These mutations resulted in truncated and altered proteins. In case 3, G>C missense mutation is found at codon 74 within helix I of HMG box (Q74H). No other mutations were found in the SRY gene of these patients. An allele-specific oligonucleotide study further confirmed that these variants are not common polymorphisms. To our knowledge, this is the first time these mutations are described at these codons resulting in mutated SRY proteins. Lack of a second sex chromosome in a majority of cells [mosaic karyotype and mutation(s) in the SRY gene] in these patients may have triggered the short stature.     

Left ventricular noncompaction (LVNC) and low mitochondrial membrane potential are specific for Barth syndrome

Barth syndrome (BTHS) is an X-linked mitochondrial defect characterised by dilated cardiomyopathy, neutropaenia and 3-methylglutaconic aciduria (3-MGCA). We report on two affected brothers with c.646G?>?A (p.G216R) TAZ gene mutations. The pathogenicity of the mutation, as indicated by the structure-based functional analyses, was further confirmed by abnormal monolysocardiolipin/cardiolipin ratio in dry blood spots of the patients as well as the occurrence of this mutation in another reported BTHS proband. In both brothers, 2D-echocardiography revealed some features of left ventricular noncompaction (LVNC) despite marked differences in the course of the disease; the eldest child presented with isolated cardiomyopathy from late infancy, whereas the youngest showed severe lactic acidosis without 3-MGCA during the neonatal period. An examination of the patients’ fibroblast cultures revealed that extremely low mitochondrial membrane potentials (mtΔΨ about 50 % of the control value) dominated other unspecific mitochondrial changes detected (respiratory chain dysfunction, abnormal ROS production and depressed antioxidant defense). 1) Our studies confirm generalised mitochondrial dysfunction in the skeletal muscle and the fibroblasts of BTHS patients, especially a severe impairment in the mtΔΨ and the inhibition of complex V activity. It can be hypothesised that impaired mtΔΨ and mitochondrial ATP synthase activity may contribute to episodes of cardiac arrhythmia that occurred unexpectedly in BTHS patients. 2) Severe lactic acidosis without 3-methylglutaconic aciduria in male neonates as well as an asymptomatic mild left ventricular noncompaction may characterise the ranges of natural history of Barth syndrome.     

<Superscript>1</Superscript>H NMR spectra of methylcitric acid in urine

Summary Methylcitric acid (3-carboxy-3-hydroxy-2-methyl-pentanedioic acid; MCA) is elevated in body fluids of patients with propionic acidaemia (PA; McKusick: 232000, 232050), methylmalonic aciduria (MMA; McKusick: 251000, 251120) and multiple carboxylase deficiency (McKusick: 253260, 253270). MCA molecule has two stereogenic centers so that it can occur in the form of four stereoisomers. Only two stereoisomers of MCA, (2S, 3S) and (2R, 3S), were found in human urine. They have different spectra and can be easily distinguished. We performed measurements of ¹H, ¹³C NMR and gs-HMQC (gradient-selected Heteronuclear Multiple Quantum Coherence) on the samples of unprocessed urine of 6 patients suffering from propionic acidaemia and methylmalonic aciduria and identified the protons of MCA diastereoisomers, 3-hydroxypropionic acid and methylmalonic acid. Having used NMR spectroscopy to identify stereoisomers of MCA in urine, we can conclude that this technique gives the possibility of analysing MCA diastereoisomers in body fluids. Electronic Supplementary Material Supplementary material is available for this article at Communicating editor: Marinus Duran     

Saccharomyces cerevisiae contains two functional genes encoding 3-hydroxy-3-methylglutaryl-coenzyme A reductase.

We have isolated two genes from yeast encoding 3-hydroxy-3-methylglutaryl-coenzyme A reductase [hydroxymethylglutaryl-coenzyme A reductase (NADPH); HMG-CoA reductase; EC 1.1.1.34], the rate-limiting enzyme of sterol biosynthesis. These genes, HMG1 and HMG2, were identified by hybridization to a cDNA clone encoding hamster HMG-CoA reductase. DNA sequence analysis reveals homology between the amino acid sequence of the proteins encoded by the two yeast genes and the carboxyl-terminal half of the hamster protein. Cells containing mutant alleles of both HMG1 and HMG2 are unable to undergo spore germination and vegetative growth. However, cells containing a mutant allele of either HMG1 or HMG2 are viable but are more sensitive to compactin, a competitive inhibitor of HMG-CoA reductase, than are wild-type cells. Assays of HMG-CoA reductase activity in extracts from hmg1- and hmg2- mutants indicate that HMG1 contributes at least 83% of the activity found in wild-type cells.     

MEFV mutations in Tunisian patients suffering from familial Mediterranean fever

OBJECTIVES: To identify the frequency and distribution of familial Mediterranean fever (FMF) gene (MEFV) mutations in Tunisian patients. PATIENTS AND METHODS: This study was performed in the Genetic Department of Tunis University Hospital. A clinical diagnosis of FMF was made according to published criteria. Mutation screening of the MEFV gene was performed in the Human Genetic Laboratory of the "Faculté de Medecine de Tunis" for 8 mutations including the 5 most common known mutations M694V, V726A, M694l, M680l, and E148Q. The tests performed were polymerase chain reaction (PCR) restriction-digestion for M694V, V726A, M680l, R761H, E148Q; amplification refractory mutation system for A744S, M694l; and PCR-electrophoresis assay for l692del. RESULTS: Of the 139 unrelated patients investigated, 61 (44%) had 1 or 2 mutations. In 78 (56%) probands no mutation was identified: 28 patients were homozygous; 16 were compound-heterozygous; 2 had complex alleles; and 17 had only 1 identifiable mutation. Of the mutations, M680l, M694V, M694l, V726A, A744S, R761H, l692DEL, and E148Q accounted for 32, 27, 13, 5, 3, 1, 1, and 18%, respectively. CONCLUSION: The profile of the MEFV gene mutations in the Tunisian population is concordant with other Arab populations but with some differences. M680l is the most common mutation, while V726A, the commonest mutation among Arabs, is rare in our population.     

A comparison of [9,10-3H]palmitic and [9,10-3H]myristic acids for the detection of defects of fatty acid oxidation in intact cultured fibroblasts

Summary The production of tritiated water from [9,10-³H]myristic acid can be used as a screening assay for the detection of medium-chain acyl-CoA dehydrogenase deficiency, multiple acyl-CoA dehydrogenation defects (glutaric aciduria type 2 and ethylmalonic-adipic aciduria types), and some types of hydroxydicarboxylic aciduria. Comparison with the release of tritiated water from [9,10-³H]palmitic acid may give an indication of the chain-length specificity of the metabolic defect. In a case of ethylmalonic-adipic aciduria such a prediction has been confirmed by examination of accumulated intermediates in the affected fibroblasts.     

SRD5B1 gene analysis needed for the accurate diagnosis of primary 3-oxo-Δ4-steroid 5β-reductase deficiency

Background and Aim:  We encounter hyper-3-oxo-Δ⁴ bile aciduria in patients with severe cholestatic liver disease or fulminant liver failure during the neonatal period. However, simply by bile acid analysis, it is difficult to distinguish hyper-3-oxo-Δ⁴ bile aciduria from primary 3-oxo-Δ⁴-steroid 5β-reductase deficiency.
Methods:  To determine whether 3-oxo-Δ⁴-steroid 5β-reductase ( SRD5B1 ) gene analysis is required for the accurate diagnosis of 3-oxo-Δ⁴-steroid 5β-reductase deficiency, we evaluated the laboratory data, bile acid analysis and SRD5B1 gene analysis from six patients with hyper-3-oxo-Δ⁴ bile aciduria.
Results:  Based upon the results, four patients who had developed neonatal liver failure were diagnosed as having neonatal hemochromatosis. Two patients with chronic cholestasis were diagnosed as having primary 3-oxo-Δ⁴-steroid 5β-reductase deficiency by SRD5B1 gene analysis. The SRD5B1 gene in these two patients had a heterozygous mutation, G737A (Gly 223 Glu) in one patient and C217T (Arg 50 stop) in the other.
Conclusions:  Based upon our limited data, we conclude that SDR5B1 gene analysis is required for the accurate diagnosis of 3-oxo-Δ⁴-steroid 5β-reductase deficiency. Moreover, we think that it is important to elucidate whether there is a heterozygous or a compound heterozygous mutation of the SRD5B1 gene in our two patients.     

Clinical phenotypes and molecular characterization of Hb H-Paksé disease

BACKGROUND AND OBJECTIVES: Hemoglobin Constant Spring (Hb CS), caused by a termination codon mutation (TAA-->CAA) in the a2 gene, is the most common non-deletional type of a thalassemia in Southeast Asia. This mutation can most easily be detected by loss of an MseI-restriction site (T/TAA) spanning the termination codon. Recently, we sequenced the a globin genes from patients with a thalassemia in whom this MseI site was absent. This revealed, a previously described termination codon mutation (TAA-->TAT) associated with Hb Paksé. This prompted us to re-evaluate the molecular basis of a thalassaemia in other Thai patients with non-deletional types of Hb H disease. DESIGN AND METHODS: DNA samples from 30 patients, previously diagnosed as having Hb H-CS disease, were characterized by direct genomic sequencing and by using a mismatched polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Clinical and hematologic data were assessed. RESULTS. Hemoglobin electrophoresis in almost all 30 unrelated patients with non-deletional a thalassemia revealed a slow migrating band resembling Hb CS. Five of these patients were found to have Hb H-Paksé disease and the remainder had Hb H-CS disease. Comparing the hematology in patients with these two genotypes, no significant differences were found except that the proportion of Hb H was higher in patients with Hb H-Paksé disease. INTERPRETATION AND CONCLUSIONS: These results suggest that termination codon mutations may have been previously misidentified in many cases of non-deletional Hb H disease. Findings from six unrelated families described in this study suggest that the proportion of patients with the Hb Paksé mutation might be underestimated and that this mutation could be prevalent in Southeast Asia. Analysis of mismatched-PCR-RFLP, described here, was shown to provide an unequivocal diagnosis and will be applicable in population screening programs.     

3-Hydroxyisobutyrate aciduria and mutations in the <Emphasis Type="Italic">ALDH6A1</Emphasis> gene coding for methylmalonate semialdehyde dehydrogenase

3-hydroxyisobutyric aciduria is an organic aciduria with a poorly understood biochemical basis. It has previously been assumed that deficiency of 3-hydroxyisobutyrate dehydrogenase (HIBADH) in the valine catabolic pathway is the underlying enzyme defect, but more recent evidence makes it likely that individuals with 3-hydroxyisobutyryic aciduria represent a heterogeneous group with different underlying mechanisms, including respiratory chain defects or deficiency of methylmalonate semialdehyde dehydrogenase. However, to date methylmalonate semialdehyde dehydrogenase deficiency has only been demonstrated at the gene level for a single individual. We present two unrelated patients who presented with developmental delay and increased urinary concentrations of 3-hydroxyisobutyric acid. Both children were products of consanguineous unions and were of European or Pakistani descent. One patient developed a febrile illness and subsequently died from a hepatoencephalopathy at 2 years of age. Further studies were initiated and included tests of the HIBADH enzyme in fibroblast homogenates, which yielded normal activities. Sequencing of the ALDH6A1 gene (encoding methylmalonate semialdehyde dehydrogenase) suggested homozygosity for the missense mutation c.785 C > A (S262Y) in exon 7 which was not found in 210 control alleles. Mutation analysis of the ALDH6A1 gene of the second patient confirmed the presence of a different missense mutation, c.184 C > T (P62S), which was also identified in 1/530 control chromosomes. Both mutations affect highly evolutionarily conserved amino acids of the methylmalonate semialdehyde dehydrogenase protein. Mutation analysis in the ALDH6A1 gene can reveal a cause of 3-hydroxyisobutyric aciduria, which may present with only slightly increased urinary levels of 3-hydroxyisobutyric acid, if a patient is metabolically stable.     

Hb Paksé [(alpha2) codon 142 (TAA-->TAT or Term-->Tyr)J in Thai patients with EAbart's disease and Hb H Disease

Hb Paksé is caused by an alpha2-globin gene termination codon mutation, TAA-->TAT or Term-->Tyr, initially described in a Laotian family. We now report for the first time that the same mutation has been found in 14 Thai patients, seven with EABart's disease, four with Hb H disease, and three with alpha-thalassemia trait who were initially diagnosed as having Hb Constant Spring (Hb CS; alpha2-globin gene termination codon mutation TAA-->CAA or Term-->Gln). Co-inheritance of this mutation with alpha-thalassemia-1 (SEA type) leads to Hb H disease (hereafter designated as Hb H-Paksé disease) and to a complex thalassemia syndrome, namely EABart's-Paksé disease. Hematological data of these patients were compared with those of classical Hb H-CS and the EABart's patients. To facilitate epidemiological and diagnostic screening of Hb Paksé, a simple assay procedure based on allele specific polymerase chain reaction (PCR) amplifications was developed and validated. Using this allele specific PCR as a screening method, five additional individuals with Hb Paksé were found among 71 Thai subjects previously thought to have Hb CS.     

Use of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in various forms of dyslipidemia

The inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase are highly effective in treating severe elevations of serum cholesterol, and are being widely used for this purpose. In our laboratory, these drugs have been used for the treatment of other forms of dyslipidemia including primary moderate hypercholesterolemia, primary mixed hyperlipidemia, diabetic dyslipidemia, hyperlipidemia of the nephrotic syndrome, and primary hypoalphalipoproteinemia. In these conditions, the HMG CoA reductase inhibitors proved effective in substantially decreasing levels of both low-density lipoproteins and very low density lipoproteins, as well as apolipoprotein B. In some patients, they may even increase levels of high-density lipoproteins. The primary mode of action of HMG CoA reductase inhibitors appears to be to increase the synthesis of hepatic receptors for lipoproteins containing apolipoprotein B, although a reduction in synthesis of these lipoproteins has not been ruled out with certainty. Regardless of mechanisms, drugs of this type appear to have the potential for effective therapy of various forms of dyslipidemia beyond primary severe hypercholesterolemia.     

Studies on the hypolipidemic and hypocholesterolemic effect of 3-hydroxy-3-methylglutaric acid in rabbits

1. (1) Administration of 3-hydroxy-3-methylglutaric acid (HMG) for one week to normal rabbits caused significant lowering of serum total, esterified and free cholesterol, total phospholipids and triglycerides. Serum lysolecithin, lecithin, sphingomyelin, and a mixture of phosphatidyl ethanolamine, serine and inositol also decreased.

2. (2) In hypercholesterolemic rabbits returned to a normal diet, two weeks' administration of HMG caused a gradual decrease in serum cholesterol and phospholipids over this period. The serum triglyceride level and aortic lipid concentrations were markedly lowered at the end of this two weeks' treatment. Serum phosphatidylethanolamine, serine, inositol and other phospholipids were lowered in these animals.

3. (3) Simultaneous administration of HMG and feeding the atherogenic diet for 54 days prevented the rise in serum cholesterol and phospholipid levels. Triglyceride levels in serum, liver and aorta were significantly reduced. Serum phosphatidyl-ethanolamine, serine and inositol substantially decreased, while cardiolipin almost disappeared.

     

A high-throughput analysis of the IDH1(R132H) protein expression in pituitary adenomas

Purpose

Inactivating mutations of isocitrate dehydrogenase (IDH) 1 and 2, mitochondrial enzymes participating in the Krebs tricarboxylic acid cycle play a role in the tumorigenesis of gliomas and also less frequently in acute myeloid leukemia and other malignancies. Inhibitors of mutant IDH1 and IDH2 may potentially be effective in the treatment of the IDH mutation driven tumors. Mutations in the succinate dehydrogenase, the other enzyme complex participating in the Krebs cycle and electron transfer of oxidative phosphorylation occur in the paragangliomas, gastrointestinal stromal tumors, and occasionally in the pituitary adenomas. We aimed to determine whether the IDH1(R132H) mutation, the most frequent IDH mutation in human malignancies, occurs in pituitary adenomas.

Methods

We performed immunohistochemical analysis by using a monoclonal anti-IDH1(R132H) antibody on the tissue microarrays containing specimens from the pituitary adenomas of different hormonal types from 246 patients. In positive samples, the status of the IDH1 gene was further examined by molecular genetic analyses.

Results

In all but one patient, there was no expression of mutated IDH1(R132H) protein in the tumor cells by immunohistochemistry. Only one patient with a recurring clinically non-functioning gonadotroph adenoma demonstrated IDH1(R132H)-immunostaining in both the primary tumor and the recurrence. However, no mutation in the IDH1 gene was detected using different molecular genetic analyses.

Conclusion

IDH1(R132H) mutation occurs only exceptionally in pituitary adenomas and does not play a role in their pathogenesis. Patients with pituitary adenomas do not seem to be candidates for treatment with the inhibitors of mutant IDH1.

     

A prevalent C3 mutation in aHUS patients causes a direct C3 convertase gain of function

Atypical hemolytic uremic syndrome (aHUS) is a rare renal thrombotic microangiopathy commonly associated with rare genetic variants in complement system genes, unique to each patient/family. Here, we report 14 sporadic aHUS patients carrying the same mutation, R139W, in the complement C3 gene. The clinical presentation was with a rapid progression to end-stage renal disease (6 of 14) and an unusually high frequency of cardiac (8 of 14) and/or neurologic (5 of 14) events. Although resting glomerular endothelial cells (GEnCs) remained unaffected by R139W-C3 sera, the incubation of those sera with GEnC preactivated with pro-inflammatory stimuli led to increased C3 deposition, C5a release, and procoagulant tissue-factor expression. This functional consequence of R139W-C3 resulted from the formation of a hyperactive C3 convertase. Mutant C3 showed an increased affinity for factor B and a reduced binding to membrane cofactor protein (MCP; CD46), but a normal regulation by factor H (FH). In addition, the frequency of at-risk FH and MCP haplotypes was significantly higher in the R139W-aHUS patients, compared with normal donors or to healthy carriers. These genetic background differences could explain the R139W-aHUS incomplete penetrance. These results demonstrate that this C3 mutation, especially when associated with an at-risk FH and/or MCP haplotypes, becomes pathogenic following an inflammatory endothelium-damaging event.     

Screening for mutation R882 in the DNMT3A gene in Chinese patients with hematological disease

The DNA (cytosine-5-)-methyltransferase 3 alpha (DNMT3A) gene is actively involved in epigenetic regulation. Mutations in this gene affect disease progression and response to therapy, particularly in hematological disease. Recent studies have demonstrated that DNMT3A gene mutations affecting codon R882 are actively involved in acute myelogenous leukemia (AML), and cause abnormal alteration of DNA methylation and poor survival. In this study, we screened DNMT3A mutations in a total of 389 Chinese patients with hematological disease by sequencing the coding region of exon 23 covering residue R882. Three heterozygous mutations (p.R882S, p.R882C and p.R882H) were identified in three of 61 AML patients, whereas none of patients with other hematological disorders harbored any mutation. Our results support the notion that DNMT3A R882 was a frequent mutation in AML patients but rare in other types of hematological disorder.