Spectrum of 5'UTR mutations in ANKRD26 gene in patients with inherited thrombocytopenia: c.-140C>G mutation is more frequent than expected

Inherited thrombocytopenia associated with a variant in the FLI1 binding site in the 5' UTR of ANKRD26

Variants in the 5' UTR of ANKRD26 are a common cause of inherited thrombocytopenia (ANKRD26-RT), and are associated with sustained ANKRD26 expression, which inhibits megakaryocyte maturation and proplatelet formation. ANKRD26 expression is controlled by the binding of a RUNX1/FLI1 complex to the 5' UTR. To date, all reported ANKRD26-RD associated variants have been within the RUNX1 binding site and a 22 base pair flanking region. Here, we report a novel variant in the 5' UTR of ANKRD26, c.-107C>T. This variant is in the FLI1 binding site, and is predicted to disrupt FLI1 binding due to loss of a hydrogen bond with FLI1. Differentiated PBMCs from affected family members showed impaired megakaryocyte maturation and proplatelet formation and sustained expression of ANKRD26, and platelets from affected family members had higher ANKRD26 expression than control platelets. The variant increased activity of the ANKRD26 promotor in a reporter assay. We also provide evidence that the previously reported c.-140C>G ANKRD26 5' UTR variant is benign and not associated with thrombocytopenia. Identification of the c.-107C>T variant extends the range of the regulatory region in the 5' UTR of ANKRD26 that is associated with ANKRD26-RT.

Analysis of clinical characteristics and treatment efficacy in two pediatric cases of ANKRD26-related thrombocytopenia

ANKRD26-related thrombocytopenia (ANKRD26-RT or THC2, MIM 188 000), an autosomal dominant thrombocytopenia, is unresponsive to immunosuppressive therapy and susceptible to hematological malignancies. A large number of pediatric patients are diagnosed with immune thrombocytopenia (ITP) every year; however, thrombocytopenia of genetic origin is often missed. Extensive characterization of ANKRD26-RT will help prevent missed diagnosis and misdiagnosis. Furthermore, identification of ANKRD26-RT will help in the formulation of an accurate diagnosis and a treatment plan. In our study, we report cases of two Chinese pediatric patients with ANKRD26-RT and analyze their clinical characteristics, gene mutations, and treatment modalities. Both patients were 1-year-old and presented with mild bleeding (World Health Organization(WHO) score grade 1), different degrees of platelet reduction, normal mean platelet volume, and megakaryocyte maturation impairment not obvious. Genetic tests revealed that both patients had ANKRD26 gene mutations.Patient 1 had a mutation c.-140C>G of the 5' untranslated region (UTR), and patient 2 had a mutation of c.-127A>T of 5'UTR. Both patients were treated with eltrombopag, and the treatment was no response, with no adverse reactions.

ANKRD26 Gene Variant of Uncertain Significance in a Patient With Acute Myeloid Leukemia

ANKRD26-related thrombocytopenia is a rare inherited disorder associated with an increased risk of malignancy. While the genetic mutations underlying this condition are well understood, there is limited knowledge regarding its contribution to myeloid neoplasms, such as acute myeloid leukemia (AML). We present a case of ANKRD26-related thrombocytopenia with a variant of uncertain significance in a patient with AML and review the pathogenesis and implications of hereditary germline mutations in disease management.

Diagnosing Czech Patients with Inherited Platelet Disorders

A single-center study was conducted on 120 patients with inherited disorders of primary hemostasis followed at our hematological center. These patients presented a variety of bleeding symptoms; however, they had no definitive diagnosis. Establishing a diagnosis has consequences for the investigation of probands in families and for treatment management; therefore, we aimed to improve the diagnosis rate in these patients by implementing advanced diagnostic methods. According to the accepted international guidelines at the time of study, we investigated platelet morphology, platelet function assay, light-transmission aggregometry, and flow cytometry. Using only these methods, we were unable to make a definitive diagnosis for most of our patients. However, next-generation sequencing (NGS), which was applied in 31 patients, allowed us to establish definitive diagnoses in six cases (variants in ANKRD26, ITGA2B, and F8) and helped us to identify suspected variants (NBEAL2, F2, BLOC1S6, AP3D1, GP1BB, ANO6, CD36, and ITGB3) and new suspected variants (GFI1B, FGA, GP1BA, and ITGA2B) in 11 patients. The role of NGS in patients with suspicious bleeding symptoms is growing and it changes the diagnostic algorithm. The greatest disadvantage of NGS, aside from the cost, is the occurrence of gene variants of uncertain significance.

ANKRD26-Related Thrombocytopenia and Predisposition to Myeloid Neoplasms

PURPOSE OF REVIEW

This review describes ANKRD26-related thrombocytopenia (RT) from a molecular, clinical, and laboratory perspective, with a focus on the clinical decision-making that takes place in the diagnosis and management of families with ANKRD26-RT.

RECENT FINDINGS

ANKRD26-related thrombocytopenia (ANKRD26-RT) is a non-syndromic autosomal dominant thrombocytopenia with predisposition to hematologic neoplasm. The clinical presentation is variable with moderate thrombocytopenia with normal platelet size and absent to mild bleeding being the hallmark which makes it difficult to distinguish from other inherited thrombocytopenias. The pathophysiology involves overexpression of ANKRD26 through loss of inhibitory control by transcription factors RUNX1 and FLI1. The great majority of disease-causing variants are in the 5' untranslated region. Acute myeloid leukemia, myelodysplastic syndrome, and chronic myelomonocytic leukemia have been reported to occur in the context of germline variants in ANKRD26, with the development of somatic driver mutations in hematopoietic regulators playing an important role in malignant transformation. In the absence of clear risk estimates of development of malignancy, optimal surveillance strategies and interventions to reduce risk of evolution to a myeloid disorder, multidisciplinary evaluation, with a strong genetic counseling framework is essential in the approach to these patients and their families. Gene-specific expertise and a multidisciplinary approach are important in the diagnosis and treatment of patients and families with ANKRD26-RT. These strategies help overcome the challenges faced by clinicians in the evaluation of individuals with a rare, non-syndromic, inherited disorder with predisposition to hematologic malignancy for which large data to guide decision-making is not available.

Prevalence and natural history of variants in the ANKRD26 gene: a short review and update of reported cases

ANKRD26 is a highly conserved gene located on chromosome 10p12.1 which has shown to play a role in normal megakaryocyte differentiation. ANKRD26-related thrombocytopenia, or thrombocytopenia 2, is an inherited thrombocytopenia with mild bleeding diathesis resulting from point mutations the 5ʹUTR of the ANKRD26 gene. Point mutations in the 5ʹUTR region have been shown to prevent transcription factor-mediated downregulation of ANKRD26 in normal megakaryocyte differentiation. Patients with ANKRD26-related thrombocytopenia have a predisposition to developing hematological malignancies, with acute myeloid leukemia and myelodysplastic syndrome most commonly described in the literature. We review the clinical features and biological mechanisms of ANKRD26-related thrombocytopenia and summarize known cases in the literature.

A novel RUNX1 mutation with ANKRD26 dysregulation is related to thrombocytopenia in a sporadic form of myelodysplastic syndrome

Aging is associated with a higher risk of developing malignant diseases, including myelodysplastic syndromes, clonal disorders characterised by chronic cytopenias (anaemia, neutropenia and thrombocytopenia) and abnormal cellular maturation. Myelodysplastic syndromes arising in older subjects are influenced by combinations of acquired somatic genetic lesions driving evolution from clonal haematopoiesis to myelodysplastic syndromes and from myelodysplastic syndromes to acute leukaemia. A different pattern of mutations has been identified in a small subset of myelodysplastic syndromes arising in young patients with familial syndromes. In particular, dysregulation of ANKRD26, RUNX1 and ETV6 genes plays a role in familial thrombocytopenia with predisposition to myelodysplastic syndromes and acute leukaemia. Whether these genes affect thrombopoiesis in sporadic myelodysplastic syndrome with thrombocytopenia is still undefined. Thirty-one myelodysplastic syndromes subjects and 27 controls subjects were investigated. Genomic DNA was used for mutation screening (ETV6, RUNX1, 5'UTR ANKRD26 genes). Functional studies were performed in the MEG-01-akaryoblastic cell line. We found four novel variants of RUNX1 gene, all in elderly myelodysplastic syndromes subjects with thrombocytopenia. Functional studies of the variant p.Pro103Arg showed no changes in RUNX1 expression, but the variant was associated with deregulated high transcriptional activity of ANKRD26 in MEG-01 cells. RUNX1 variant p.Pro103Arg was also associated with increased viability and reduced apoptosis of MEG-01, as well as impaired platelet production. Our findings are consistent with dysregulation of ANKRD26 in RUNX1 haploinsufficiency. Lack of repression of ANKRD26 expression may contribute to thrombocytopenia of subjects with sporadic myelodysplastic syndromes.

Inherited Thrombocytopenia Caused by Germline ANKRD26 Mutation Should Be Considered in Young Patients With Suspected Myelodysplastic Syndrome

Thrombocytopenia 2 (THC2) is an autosomal dominant disorder characterized by ankyrin repeat domain 26 mutation and moderate thrombocytopenia. THC2 exposes patients to a low risk of bleeding and an increased likelihood of myelodysplastic syndrome/acute myeloid leukemia. Germline evaluation for a genetic disorder should be considered when a patient presents with isolated thrombocytopenia and associated dysmegakaryopoiesis. In this case report, we present a male patient who presented with isolated thrombocytopenia but was ultimately confirmed to have an inherited THC2 thrombocytopenia/myelodysplastic syndrome. Given the rarity of the disease, no clear guidelines on how to follow THC2 patients over the long term have been established. We recommend a monthly complete blood count and clinical visits every 3 months at a minimum.

Inherited Platelet Disorders: An Updated Overview

Platelets play a major role in hemostasis as ppwell as in many other physiological and pathological processes. Accordingly, production of about 10¹¹ platelet per day as well as appropriate survival and functions are life essential events. Inherited platelet disorders (IPDs), affecting either platelet count or platelet functions, comprise a heterogenous group of about sixty rare diseases caused by molecular anomalies in many culprit genes. Their clinical relevance is highly variable according to the specific disease and even within the same type, ranging from almost negligible to life-threatening. Mucocutaneous bleeding diathesis (epistaxis, gum bleeding, purpura, menorrhagia), but also multisystemic disorders and/or malignancy comprise the clinical spectrum of IPDs. The early and accurate diagnosis of IPDs and a close patient medical follow-up is of great importance. A genotype-phenotype relationship in many IPDs makes a molecular diagnosis especially relevant to proper clinical management. Genetic diagnosis of IPDs has been greatly facilitated by the introduction of high throughput sequencing (HTS) techniques into mainstream investigation practice in these diseases. However, there are still unsolved ethical concerns on general genetic investigations. Patients should be informed and comprehend the potential implications of their genetic analysis. Unlike the progress in diagnosis, there have been no major advances in the clinical management of IPDs. Educational and preventive measures, few hemostatic drugs, platelet transfusions, thrombopoietin receptor agonists, and in life-threatening IPDs, allogeneic hematopoietic stem cell transplantation are therapeutic possibilities. Gene therapy may be a future option. Regular follow-up by a specialized hematology service with multidisciplinary support especially for syndromic IPDs is mandatory.

Relation between mutations in the 5' UTR of ANKRD26 gene and inherited thrombocytopenia with predisposition to myeloid malignancies. An Egyptian study

Inherited thrombocytopenias are a heterogeneous group of diseases characterized by a reduced number of platelets and a bleeding tendency that ranges from very mild to life threatening especially in surgery. Mutations in the 5' untranslated region (UTR) of Ankirin repeat domain 26 (ANKRD26) are responsible for autosomal-dominant form of thrombocytopenia, that is known as ANKRD26-related thrombocytopenia (ANKRD26 RT), characterized by a moderate thrombocytopenia with mild propensity to bleeding and predisposition to hematological malignancies including AML and MDS. We included 90 unrelated patients with inherited thrombocytopenia. In addition, we investigated 45 patients with ITP. Peripheral blood and bone marrow samples were collected and examined and molecular detection of mutations in the 5︡ UTR of ANKRD26 gene was performed for all the patients. Also, screening of the mutation and development of myeloid malignancies in the extended series of the affected subjects was done. ANKRD26 mutations were identified in 10% of the patients with inherited thrombocytopenia. The most common types were c.128 G > A and c.127A>T, while no mutations were found in the ITP group. In those affected, the median number of platelets was 69 x10⁹/L (43-106) with normal MPV in most of the patients (9.4-11.6). There was a statistically significant increase in the unexpected high frequency of myeloid malignancies in the extended series of the mutated subjects compared with the ITP group-extended series (P < .001). So, we can conclude that ANKRD26 RT is associated with increased risk for developing myeloid malignancies and ANKRD26 mutations can represent a valuable tool for making therapeutic decisions.

A Rare Big Chinese Family With Thrombocytopenia 2: A Case Report and Literature Review

Thrombocytopenia 2 (THC2) is one of the most prevalent forms of inherited thrombocytopenia. It is caused by a heterogeneous group of ANKRD26 gene mutation and shows a heterogeneous clinical and laboratory characteristics. We present a big Chinese family with 10 THC2 patients carrying c.-128G > T heterozygous substitution in the 5-untranslated region of the ANKRD26 gene. Although the platelets are fewer than 50 × 10⁹/L in 8 THC2 family members, only the proband and her son show a higher WHO bleeding score. The proband and her son are also beta-thalassemia carriers with heterozygous c.52A > T mutation of HBB, which might not be associated with the increased bleeding tendency since 3 other family members with low bleeding tendency also carried both ANKRD26 c.-128G > T and HBB c.52A > T mutations. However, the proband and her son also show hypofibrinogenaemia, which is likely the cause of their more severe clinical manifestation. HID1 c.442G > T mutation was detected not only in these two hypofibrinogenaemia family members but also in the other 8 family members with normal blood fibrinogen levels. Our study suggests that the co-occurrence of other inherited genetic conditions associated with blood coagulation might contribute to the heterogeneity of clinical and laboratory characteristics in THC2 patients. Considering the hematologic and myeloid malignancy predisposition of THC2 patients and a large population of immune thrombocytopenia in China, we urge more attention to be paid to the diagnosis of THC2 patients to avoid misdiagnosis and mistreatment.

A new NOTCH3 damaging variant in a thrombocytopenia family of Miao ethnic group

BACKGROUND

Pediatric inherited thrombocytopenia, also known as a deficiency of platelets in children, is caused by genetic factors and it is hard to obtain an effective treatment. Thus, it is necessary to identify the possible genetic variants that are responsible for thrombocytopenia.

METHODS

Whole exome sequencing was used to detect genetic variants in two members of a thrombocytopenia family of Miao ethnic group. Multiple in silico analyses were performed to evaluate the effects of the novel missense variants.

RESULTS

Finally, a novel variant (chr19: g.15170364G>A) in the NOTCH3 gene was found, as confirmed with Sanger sequencing, which could result in a R1694Q substitution in the protein. This variant was consistently suggested to be damaging by sift (Sorting Tolerant From Intolerant; http://sift.jcvi.org), polyphen (Polymorphism Phenotyping, version 2.0; http://genetics.bwh.harvard.edu/pph2) and mutationtaster (http://www.mutationtaster.org) software. By building the 3D model of the key region of NOTCH3 protein and performing the structure simulation, we found that (i) this variant affected the 3D structure model with a root-mean-square deviation = 0.46 between wild-type and mutant type; (ii) this variant caused the protein to reduce the solvent accessible surface area by 421 Å² ; and (iii) compared to the wild-type protein, the mutant protein had two less amino acids to maintain protein stability.

CONCLUSIONS

A novel damaging variant in the NOTCH3 gene was identified in a thrombocytopenia family with respect to decreasing the stability of NOTCH3, which may help with the prognosis and therapy of inherited thrombocytopenia.

Inherited thrombocytopenia and platelet disorders with germline predisposition to myeloid neoplasia

Advances in molecular genetic sequencing techniques have contributed to the elucidation of previously unknown germline mutations responsible for inherited thrombocytopenia (IT). Regardless of age of presentation and severity of symptoms related to thrombocytopenia and/or platelet dysfunction, a subset of patients with IT are at increased risk of developing myeloid neoplasms during their life time, particularly those with germline autosomal dominant mutations in RUNX1, ANKRD26, and ETV6. Patients may present with isolated thrombocytopenia and megakaryocytic dysmorphia or atypia on baseline bone marrow evaluation, without constituting myelodysplasia (MDS). Bone marrow features may overlap with idiopathic thrombocytopenic purpura (ITP) or sporadic MDS leading to misdiagnosis. Progression to myelodysplastic syndrome/ acute myeloid leukemia (MDS/AML) may be accompanied by progressive bi- or pancytopenia, multilineage dysplasia, increased blasts, cytogenetic abnormalities, acquisition of bi-allelic mutations in the underlying gene with germline mutation, or additional somatic mutations in genes associated with myeloid malignancy. A subset of patients may present with MDS/AML at a young age, underscoring the growing concern for evaluating young patients with MDS/AML for germline mutations predisposing to myeloid neoplasm. Early recognition of germline mutation and predisposition to myeloid malignancy permits appropriate treatment, adequate monitoring for disease progression, proper donor selection for hematopoietic stem cell transplantation, as well as genetic counseling of the affected patients and their family members. Herein, we describe the clinical and diagnostic features of IT with germline mutations predisposing to myeloid neoplasms focusing on mutations involving RUNX1, ANKRD26, and ETV6.

Fructosuria and recurrent hypoglycemia in a patient with a novel c.1693T>A variant in the 3' untranslated region of the aldolase B gene

Hereditary fructose intolerance, caused by mutations in the ALDOB gene, is an unusual cause of hypoglycemia. ALDOB encodes the enzyme aldolase B, responsible for the hydrolysis of fructose 1-phosphate in the liver. Here, we report the case of a 33-year-old female patient who consulted due to repetitive episodes of weakness, dizziness and headache after food ingestion. An ambulatory 72-h continuous glucose monitoring revealed multiple short hypoglycemic episodes over the day. After biochemical exclusion of other endocrine causes of hypoglycemia, hereditary fructose intolerance seemed a plausible diagnosis. Repeated measurements of urinary fructose revealed pathologic fructosuria, but genetic testing for the three most common mutations in ALDOB resulted negative. We decided to perform complete Sanger sequencing of the ALDOB gene and encountered a variant consisting of a T>A substitution in position 1963 of the ALDOB transcript (c.1693T>A). This position is located within the 3′ untranslated region of exon 9, 515 nucleotides downstream the stop codon. After complete withdrawal of dietary fructose and sucrose, the patient presented no new hypoglycemic episodes.