Trisomy 21 in neoplastic cells

Selection forces underlying aneuploidy patterns in cancer

Aneuploidy, the presence of an aberrant number of chromosomes, has been associated with tumorigenesis for over a century. More recently, advances in karyotyping techniques have revealed its high prevalence in cancer: About 90% of solid tumors and 50-70% of hematopoietic cancers exhibit chromosome gains or losses. When analyzed at the level of specific chromosomes, there are strong patterns that are observed in cancer karyotypes both pan-cancer and for specific cancer types. These specific aneuploidy patterns correlate strongly with outcomes for tumor initiation, progression, metastasis formation, immune evasion and resistance to therapeutic treatment. Despite their prominence, understanding the basis underlying aneuploidy patterns in cancer has been challenging. Advances in genetic engineering and bioinformatic analyses now offer insights into the genetic determinants of aneuploidy pattern selection. Overall, there is substantial evidence that expression changes of particular genes can act as the positive selective forces for adaptation through aneuploidy. Recent findings suggest that multiple genes contribute to the selection of specific aneuploid chromosomes in cancer; however, further research is necessary to identify the most impactful driver genes. Determining the genetic basis and accompanying vulnerabilities of specific aneuploidy patterns is an essential step in selectively targeting these hallmarks of tumors.

Hematologic Neoplasms Associated with Down Syndrome: Cellular and Molecular Heterogeneity of the Diseases

The molecular basis of Down syndrome (DS) predisposition to leukemia is not fully understood but involves various factors such as chromosomal abnormalities, oncogenic mutations, epigenetic alterations, and changes in selection dynamics. Myeloid leukemia associated with DS (ML-DS) is preceded by a preleukemic phase called transient abnormal myelopoiesis driven by GATA1 gene mutations and progresses to ML-DS via additional mutations in cohesin genes, CTCF, RAS, or JAK/STAT pathway genes. DS-related ALL (ALL-DS) differs from non-DS ALL in terms of cytogenetic subgroups and genetic driver events, and the aberrant expression of CRLF2, JAK2 mutations, and RAS pathway-activating mutations are frequent in ALL-DS. Recent advancements in single-cell multi-omics technologies have provided unprecedented insights into the cellular and molecular heterogeneity of DS-associated hematologic neoplasms. Single-cell RNA sequencing and digital spatial profiling enable the identification of rare cell subpopulations, characterization of clonal evolution dynamics, and exploration of the tumor microenvironment's role. These approaches may help identify new druggable targets and tailor therapeutic interventions based on distinct molecular profiles, ultimately improving patient outcomes with the potential to guide personalized medicine approaches and the development of targeted therapies.

Gain of chromosome 21 increases the propensity for P2RY8::CRLF2 acute lymphoblastic leukemia via increased HMGN1 expression

Acute lymphoblastic leukemia (ALL) patients with a gain of chromosome 21, intrachromosomal amplification of chromosome 21 (iAMP21), or Down syndrome (DS), have increased expression of genes in the DS critical region (DSCR) of chromosome 21, including the high-mobility group nucleosome-binding protein 1, HMGN1. Children with DS are predisposed to develop hematologic malignancies, providing insight into the role of chromosome 21 in the development of leukemias. A 320-kb deletion in the pseudoautosomal region of the X/Y chromosome in leukemic cells, resulting in a gene fusion between the purinergic receptor and cytokine receptor-like factor-2 (P2Y Receptor Family Member 8 (P2RY8)::CRLF2), is a common feature in ~60% of DS-ALL and ~40% of iAMP21 patients, suggesting a link between chromosome 21 and P2RY8::CRLF2. In an Australian cohort of pediatric B-ALL patients with P2RY8::CRLF2 (n = 38), eight patients harbored gain of chromosome 21 (+21), and two patients had iAMP21, resulting in a significantly increased HMGN1 expression. An inducible CRISPR/Cas9 system was used to model P2RY8::CRLF2 and investigate its cooperation with HMGN1. This model was then used to validate HMGN1 as an influencing factor for P2RY8::CRLF2 development. Using Cas9 to cleave the DNA at the pseudoautosomal region without directed repair, cells expressing HMGN1 favored repair, resulting in P2RY8::CRLF2 generation, compared with cells without HMGN1. CRISPR/Cas9 P2RY8::CRLF2 cells expressing HMGN1 exhibit increased proliferation, thymic stromal lymphopoietin receptor (TSLPR) expression, and JAK/STAT signaling, consistent with cells from patients with P2RY8::CRLF2. Our patient expression data and unique CRISPR/Cas9 modeling, when taken together, suggest that HMGN1 increases the propensity for P2RY8::CRLF2 development. This has important implications for patients with DS, +21, or iAMP21.

Acute Megakaryocytic Leukemia

Acute megakaryoblastic leukemia (AMKL) is a rare malignancy affecting megakaryocytes, platelet-producing cells that reside in the bone marrow. Children with Down syndrome (DS) are particularly prone to developing the disease and have a different age of onset, distinct genetic mutations, and better prognosis as compared with individuals without DS who develop the disease. Here, we discuss the contributions of chromosome 21 genes and other genetic mutations to AMKL, the clinical features of the disease, and the differing features of DS- and non-DS-AMKL. Further studies elucidating the role of chromosome 21 genes in this disease may aid our understanding of how they function in other types of leukemia, in which they are frequently mutated or differentially expressed. Although researchers have made many insights into understanding AMKL, much more remains to be learned about its underlying molecular mechanisms.

CRISPR/Cas9-Directed Reassignment of the GATA1 Initiation Codon in K562 Cells to Recapitulate AML in Down Syndrome

Using a CRISPR/Cas9 system, we have reengineered a translational start site in the GATA1 gene in K562 cells. This mutation accounts largely for the onset of myeloid leukemia in Down syndrome (ML-DS). For this reengineering, we utilized CRISPR/Cas9 to generate mammalian cell lines that express truncated versions of the Gata1s protein similar to that seen in ML-DS, as determined by analyzing specific genetic alterations resulting from CRISPR/Cas9 cleavage. During this work, 73 cell lines were clonally expanded, with allelic variance analyzed. Using Tracking of Indels by DEcomposition (TIDE) and Sanger sequencing, we defined the DNA sequence and variations within each allele. We found significant heterogeneity between alleles in the same clonally expanded cell, as well as among alleles from other clonal expansions. Our data demonstrate and highlight the importance of the randomness of resection promoted by non-homologous end joining after CRISPR/Cas9 cleavage in cells undergoing genetic reengineering. Such heterogeneity must be fully characterized to predict altered functionality inside target tissues and to accurately interpret the associated phenotype. Our data suggest that in cases where the objective is to rearrange specific nucleotides to redirect gene expression in human cells, it is imperative to analyze genetic composition at the individual allelic level.

Aneuploidy impairs hematopoietic stem cell fitness and is selected against in regenerating tissues in vivo

Pfau et al. evaluated the fitness of cells with constitutional trisomy or chromosomal instability (CIN) in vivo and found that aneuploid hematopoietic stem cells (HSCs) exhibit decreased fitness. Analyses of mice with CIN caused by a hypomorphic mutation in the gene Bub1b showed that while nonregenerating adult tissues are highly aneuploid, HSCs and other regenerative adult tissues are largely euploid.

Aneuploidy, an imbalanced karyotype, is a widely observed feature of cancer cells that has long been hypothesized to promote tumorigenesis. Here we evaluate the fitness of cells with constitutional trisomy or chromosomal instability (CIN) in vivo using hematopoietic reconstitution experiments. We did not observe cancer but instead found that aneuploid hematopoietic stem cells (HSCs) exhibit decreased fitness. This reduced fitness is due at least in part to the decreased proliferative potential of aneuploid hematopoietic cells. Analyses of mice with CIN caused by a hypomorphic mutation in the gene Bub1b further support the finding that aneuploidy impairs cell proliferation in vivo. Whereas nonregenerating adult tissues are highly aneuploid in these mice, HSCs and other regenerative adult tissues are largely euploid. These findings indicate that, in vivo, mechanisms exist to select against aneuploid cells.

Aurea mediocritas: the importance of a balanced genome

Aneuploidy, defined as an abnormal number of chromosomes, is a hallmark of cancer. Paradoxically, aneuploidy generally has a negative impact on cell growth and fitness in nontransformed cells. In this work, we review recent progress in identifying how aneuploidy leads to genomic and chromosomal instability, how cells can adapt to the deleterious effects of aneuploidy, and how aneuploidy contributes to tumorigenesis in different genetic contexts. Finally, we also discuss how aneuploidy might be a target for anticancer therapies.

Biological and clinical features of trisomy 21 in adult patients with acute myeloid leukemia

INTRODUCTION

Trisomy 21 is frequently noted in patients with AML. In adults, +21 has traditionally been considered an intermediate-risk cytogenetic aberration.

PATIENTS AND METHODS

We analyzed 90 patients with newly diagnosed AML harboring +21. Four cytogenetic subgroups were defined based on associated cytogenetic abnormalities: +21 alone, +21 with favorable, +21 with intermediate, and +21 with unfavorable cytogenetics.

RESULTS

Fifty-four percent of patients with +21 AML achieved a complete remission (CR) or CR with incomplete platelet recovery (CRp) after induction therapy with a trend toward improved CR/CRp rates in patients with +21 alone/+21 with favorable cytogenetics compared with patients with +21 with intermediate/+21 with unfavorable cytogenetics (76% vs. 50%; P = .057). Time to progression (TTP) was 12 months (range, 5-19) and overall survival (OS) was 9 months (range, 7-11) for the entire group. TTP was longer for patients with +21 alone (not reached) or with +21 with favorable cytogenetics (101 months) compared with those with +21 with intermediate cytogenetics (2 months) or +21 with unfavorable cytogenetics (11 months) (P = .02). Similarly, OS was improved in patients with +21 with favorable cytogenetics (not reached) or +21 alone (107 months), compared with +21 with unfavorable cytogenetics (9 months) or +21 with intermediate cytogenetics (8 months) (P < .001). The differences in TTP and OS were maintained on multivariate analysis (P = .04 and P = .001; respectively).

CONCLUSION

Isolated +21 hitherto classified as intermediate-risk cytogenetics might actually behave as a favorable-risk cytogenetics in adult AML patients.

Alterations and chromosomal variants in the Ecuadorian population

Medical genetics is a field marked by fast progress. Even though it was at one point confined to a group of relatively rare diseases, today it has become a central component in the understanding of disorders and it is the subject of interest for all medical specialties. This paper, shares data on the chromosomal alterations and variations that have been diagnosed in Ecuadorian patients since 1998. A total of 2,636 individual cases have been analyzed by G-banding technique until February 2012. The present work shows this collection of data and the important findings that have appeared throughout these years in hopes that it can contribute to have a deeper understanding of the incidence of chromosomal aberrations and alterations in the Ecuadorian population.

Chromosomal instability and aneuploidy in cancer: from yeast to man

Aneuploidy is frequently associated with disease and developmental abnormalities. It is also a key characteristic of cancer. Several model systems have been developed to study the role of chromosomal instability and aneuploidy in tumorigenesis. The results are surprisingly complex, with the conditions sometimes promoting and sometimes inhibiting tumour formation. Here, we review the effects of aneuploidy and chromosomal instability in cells and model systems of cancer, propose a model that could explain these complex findings and discuss how the aneuploid condition could be exploited in cancer therapy.

Increased dosage of the chromosome 21 ortholog Dyrk1a promotes megakaryoblastic leukemia in a murine model of Down syndrome

Individuals with Down syndrome (DS; also known as trisomy 21) have a markedly increased risk of leukemia in childhood but a decreased risk of solid tumors in adulthood. Acquired mutations in the transcription factor-encoding GATA1 gene are observed in nearly all individuals with DS who are born with transient myeloproliferative disorder (TMD), a clonal preleukemia, and/or who develop acute megakaryoblastic leukemia (AMKL). Individuals who do not have DS but bear germline GATA1 mutations analogous to those detected in individuals with TMD and DS-AMKL are not predisposed to leukemia. To better understand the functional contribution of trisomy 21 to leukemogenesis, we used mouse and human cell models of DS to reproduce the multistep pathogenesis of DS-AMKL and to identify chromosome 21 genes that promote megakaryoblastic leukemia in children with DS. Our results revealed that trisomy for only 33 orthologs of human chromosome 21 (Hsa21) genes was sufficient to cooperate with GATA1 mutations to initiate megakaryoblastic leukemia in vivo. Furthermore, through a functional screening of the trisomic genes, we demonstrated that DYRK1A, which encodes dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A, was a potent megakaryoblastic tumor-promoting gene that contributed to leukemogenesis through dysregulation of nuclear factor of activated T cells (NFAT) activation. Given that calcineurin/NFAT pathway inhibition has been implicated in the decreased tumor incidence in adults with DS, our results show that the same pathway can be both proleukemic in children and antitumorigenic in adults.

Myeloid leukemia in Down syndrome

Although adults with Down syndrome (DS) show a decreased incidence of cancer compared to individuals without DS, children with DS are at an increased risk of leukemia. Nearly half of these childhood leukemias are classified as acute megakaryoblastic leukemia (AMKL), a relatively rare subtype of acute myeloid leukemia (AML). Here, we summarize the clinical features of myeloid leukemia in DS, review recent research on the mechanisms of leukemogenesis, including the roles of GATA1 mutations and trisomy 21, and discuss treatment strategies. Given that trisomy 21 is a relatively common event in hematologic malignancies, greater knowledge of how the genes on chromosome 21 contribute to DS-AMKL will increase our understanding of a broader class of patients with leukemia.

Germinal and Somatic Trisomy 21 Mosaicism: How Common is it, What are the Implications for Individual Carriers and How Does it Come About?

It is well known that varying degrees of mosaicism for Trisomy 21, primarily a combination of normal and Trisomy 21 cells within individual tissues, may exist in the human population. This involves both Trisomy 21 mosaicism occurring in the germ line and Trisomy 21 mosaicism documented in different somatic tissues, or indeed a combination of both in the same subjects. Information on the incidence of Trisomy 21 mosaicism in different tissue samples from people with clinical features of Down syndrome as well as in the general population is, however, still limited. One of the main reasons for this lack of detailed knowledge is the technological problem of its identification, where in particular low grade/cryptic Trisomy 21 mosaicism, i.e. occurring in less than 3-5% of the respective tissues, can only be ascertained by fluorescence in situ hybridization (FISH) methods on large cell populations from the different tissue samples.In this review we summarize current knowledge in this field with special reference to the question on the likely incidence of germinal and somatic Trisomy 21 mosaicism in the general population and its mechanisms of origin. We also highlight the reproductive and clinical implications of this type of aneuploidy mosaicism for individual carriers. We conclude that the risk of begetting a child with Trisomy 21 Down syndrome most likely is related to the incidence of Trisomy 21 cells in the germ line of any carrier parent. The clinical implications for individual carriers may likewise be dependent on the incidence of Trisomy 21 in the relevant somatic tissues. Remarkably, for example, there are indications that Trisomy 21 mosaicism will predispose carriers to conditions such as childhood leukemia and Alzheimer's Disease but there is on the other hand a possibility that the risk of solid cancers may be substantially reduced.

CD19-positive acute myeloblastic leukemia with trisomy 21 as a sole acquired karyotypic abnormality

We report that a 63-year-old Chinese female had acute myeloblastic leukemia (AML) in which trisomy 21 (+21) was found as the sole acquired karyotypic abnormality. The blasts were positive for myeloperoxidase, and the immunophenotype was positive for cluster of differentiation 19 (CD19), CD33, CD34, and human leukocyte antigens (HLA)-DR. The chromosomal analysis of bone marrow showed 47,XX,+21[2]/46,XX[18]. Fluorescent in situ hybridization (FISH) showed that three copies of AML1 were situated in separate chromosomes, and that t(8;21) was negative. The patient did not have any features of Down syndrome. A diagnosis of CD19-positive AML-M5 was established with trisomy 21 as a sole acquired karyotypic abnormality. The patient did not respond well to chemotherapy and died three months after the diagnosis. This is the first reported case of CD19-positive AML with trisomy 21 as the sole cytogenetic abnormality. The possible prognostic significance of the finding in AML with +21 as the sole acquired karyotypic abnormality was discussed.

Exposure to medical test irradiation and acute leukemia among children with Down syndrome: a report from the Children's Oncology Group

OBJECTIVE

The etiology of acute childhood leukemia is not well understood, particularly among children with Down syndrome, in whom a 10- to 20-fold increased risk of leukemogenesis has been reported compared with children without Down syndrome. We explored the association between medical test irradiation, a postulated leukemogenic agent, and acute leukemia among children with Down syndrome.

PATIENTS AND METHODS

Children with Down syndrome (controls) were frequency matched on age to children with Down syndrome and leukemia (cases) diagnosed at ages 0 to 19 years during the period 1997-2002 at participating Children's Oncology Group institutions in North America. Telephone interviews were completed with mothers of 158 cases (n = 97 acute lymphoblastic leukemia and n = 61 acute myeloid leukemia) and 173 controls. Paternal interviews were completed with 275 fathers and 40 mothers serving as surrogates. Three irradiation exposure periods were examined: preconception, in utero, and postnatal. Multivariate unconditional logistic regression models were constructed to evaluate the associations of interest, resulting in odds ratios and 95% confidence intervals.

RESULTS

There was little evidence that maternal or paternal preconception irradiation exposure, intrauterine exposure, or postnatal exposure contributes to leukemogenesis in children with Down syndrome. Overall, no evidence for an effect of any periconceptional exposure was observed. Similar results were observed among acute lymphoblastic leukemia and acute myeloid leukemia cases analyzed separately.

CONCLUSIONS

This was the first study, to our knowledge, to examine such an association among this unique patient population. The results do not provide evidence of a positive association between ionizing radiation exposure and acute leukemia among children with Down syndrome. The absence of an association should be encouraging for concerned parents of children with Down syndrome who undergo a series of diagnostic radiographs in the course of their standard care.

Recent insights into the mechanisms of myeloid leukemogenesis in Down syndrome

GATA-1 is the founding member of a transcription factor family that regulates growth and maturation of a diverse set of tissues. GATA-1 is expressed primarily in hematopoietic cells and is essential for proper development of erythroid cells, megakaryocytes, eosinophils, and mast cells. Although loss of GATA-1 leads to differentiation arrest and apoptosis of erythroid progenitors, absence of GATA-1 promotes accumulation of immature megakaryocytes. Recently, we and others have reported that mutagenesis of GATA1 is an early event in Down syndrome (DS) leukemogenesis. Acquired mutations in GATA1 were detected in the vast majority of patients with acute megakaryoblastic leukemia (DS-AMKL) and in nearly every patient with transient myeloproliferative disorder (TMD), a "preleukemia" that may be present in as many as 10% of infants with DS. Although the precise pathway by which mutagenesis of GATA1 contributes to leukemia is unknown, these findings confirm that GATA1 plays an important role in both normal and malignant hematopoiesis. Future studies to define the mechanism that results in the high frequency of GATA1 mutations in DS and the role of altered GATA1 in TMD and DS-AMKL will shed light on the multistep pathway in human leukemia and may lead to an increased understanding of why children with DS are markedly predisposed to leukemia.

Myelodysplastic syndromes in childhood: a population based study of nine cases

Nine cases of de novo myelodysplastic syndromes (MDS) in childhood from a population based study are presented. The annual incidence of MDS was 3.4/1,000,000 in children less than 15 years old, corresponding to 8.7% of all haematological malignancies in childhood. Two patients had Down's syndrome. None of the remaining patients had constitutional anomalies. All patients were classified according to the FAB classification. Five patients presented with refractory anaemia (RA), only one of these did not progress, one showed clonal evolution, and the remaining three patients all progressed to refractory anaemia with excess of blasts (RAEB). Three patients presented with RAEB. Two progressed to overt leukaemia. The last patient was classified as chronic myelomonocytic leukaemia (CMML). Clonal cytogenetic abnormalities were detected in five patients, in three of them as monosomy 7. Five patients have died; two of progressive disease, two of infections, and one of haemorrhage, two of the latter three patients died during therapy induced cytopenia. Of the four patients still alive, one patient showed a complete remission after cyclosporine and later immunoglobulin therapy, one patient is a long-term survivor after allogeneic bone marrow transplantation, and one patient apparently obtained a spontaneous remission several months after chemotherapy.