Leukaemia arising in donor cells following allogeneic bone marrow transplantation for beta thalassaemia demonstrated by immunological, DNA and molecular cytogenetic analysis

Far from Health: The Bone Marrow Microenvironment in AML, A Leukemia Supportive Shelter

Acute myeloid leukemia (AML) is the second most common leukemia among children. Although significant progress in AML therapy has been achieved, treatment failure is still associated with poor prognosis, emphasizing the need for novel, innovative therapeutic approaches. To address this major obstacle, extensive knowledge about leukemogenesis and the complex interplay between leukemic cells and their microenvironment is required. The tremendous role of this bone marrow microenvironment in providing a supportive and protective shelter for leukemic cells, leading to disease development, progression, and relapse, has been emphasized by recent research. It has been revealed that the interplay between leukemic cells and surrounding cellular as well as non-cellular components is critical in the process of leukemogenesis. In this review, we provide a comprehensive overview of recently gained knowledge about the importance of the microenvironment in AML whilst focusing on promising future therapeutic targets. In this context, we describe ongoing clinical trials and future challenges for the development of targeted therapies for AML.

Comparative assessment of the acute toxicity, haematological and genotoxic effects of ten commonly used pesticides on the African Catfish, Clarias gariepinus Burchell 1822

Freshwater fishes are faced with increasing threats due to intensification of agriculture. This study evaluated the haematological and genotoxic effects of exposure of the African Catfish, Clarias gariepinus to sublethal concentrations of commonly used pesticides in agricultural settings. The evaluated pesticides were abamectin, carbofuran, chlorpyrifos, cypermethrin, deltamethrin, dichlorvos, dimethoate, fipronil, lambda-cyhalothrin and paraquat. The fishes were initially exposed singly to the pesticides for 96 h periods to determine their LC₅₀, followed by exposure to sublethal concentrations (1/100^th 96 h LC₅₀) over a 21 d period. In all cases, a control experiment with catfishes kept in dechlorinated municipal water was monitored simultaneously. The 96 h LC₅₀ values was found to vary widely from 2.043 μgL^-1 (Lambda-cyhalothrin) to 10284.288 μgL^-1(Paraquat). Significant differences (P < 0.05) were observed between mean haematological parameters-WBC, RBC, HGB, HCT, MCH and MCHC in the exposed and control catfishes. More so, micronucleus and nuclear abnormalities occurred at significantly higher proportions in pesticide exposed catfishes. Holistic cradle to grave approach as well as fate analysis is required to mitigate the potential harmful effects of pesticides to fresh water fishes.

ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the age-dependent sensitivity to radiation carcinogenesis, including the effects of in-utero exposure.

Donor cell-derived leukemia after cord blood transplantation and a review of the literature: differences between cord blood and BM as the transplant source

Donor cell-derived leukemia (DCL) is a rare complication of SCT. Here, we present a case of DCL following cord blood transplantation (CBT) and review the clinical features of previously reported DCL. To our knowledge, this is the first report comparing clinical characteristics of DCL from the standpoint of the transplant source, with umbilical cord blood and BM. AML and myelodysplastic syndrome (MDS) were recognized more frequently in DCL after CBT, whereas the incidence of AML and ALL was similar after BMT. The median duration between the occurrence of DCL following CBT and BMT was 14.5 and 36 months, respectively. DCL occurred in a significantly shorter period after CBT than after BMT. Abnormal karyotypes involving chromosome 7 were observed in 52.4% of CBT recipients and 17.3% of BMT recipients; this was a statistically significant difference. Particularly, the frequency of monosomy 7 was significantly higher in DCL after CBT than after BMT. The types of abnormal karyotypes in DCL following BMT were similar to those characteristically observed in adult de novo AML and MDS. DCL patients generally have a poor prognosis in both groups. SCT is the best treatment for curing DCL. DCL appears to have different clinical features according to the transplant source.

Donor cell-derived leukemias/myelodysplastic neoplasms in allogeneic hematopoietic stem cell transplant recipients: a clinicopathologic study of 10 cases and a comprehensive review of the literature

We report 10 cases of donor cell leukemia (DCL). All cases except the case of chronic lymphocytic leukemia had anemia, neutropenia, and/or thrombocytopenia when DCL was diagnosed. Eight cases with sex-mismatched hematopoietic stem cell transplant (HCT) showed donor gonosomal complements, suggesting DCL. Clonal cytogenetic abnormalities were detected in 8 cases: 6 were monosomy 7/del(7q). In all 10 cases, engraftment studies confirmed donor cell origin. Retrospective fluorescence in situ hybridization in archived donor cells in 4 cases showed a low level of abnormalities in 2. Of 7 patients with clinical follow-up of 5 months or more, 1 (with acute myeloid leukemia) died of disease; 6 are alive, including 1 with myelodysplastic syndrome with spontaneous remission. Similar to reported cases, we found disproportional sex-mismatched HCTs, suggesting probable underdetection of DCL in sex-matched HCTs. The latency between HCT and DCL ranged from 1 to 193 months (median, 24 months), in keeping with the literature. Analyzing our cases, pooled with reported cases, with survival models showed much shorter latency for malignancy as primary disease, for T-cell large granular lymphocyte leukemia as type of DCL, and for umbilical cord blood as stem cell source.

Donor cell leukemia: a review

Relapse of acute leukemia following hematopoietic stem cell transplantation (HSCT) usually represents return of an original disease clone, having evaded eradication by pretransplant chemo-/radiotherapy, conditioning, or posttransplant graft-versus-leukemia (GVL) effect. Rarely, acute leukemia can develop de novo in engrafted cells of donor origin. Donor cell leukemia (DCL) was first recognized in 1971, but for many years, the paucity of reported cases suggested it to be a rare phenomenon. However, in recent years, an upsurge in reported cases (in parallel with advances in molecular chimerism monitoring) suggest that it may be significantly more common than previously appreciated; emerging evidence suggests that DCL might represent up to 5% of all posttransplant leukemia "relapses." Recognition of DCL is important for several reasons. Donor-derivation of the leukemic clone has implications when selecting appropriate therapy, because seeking to enhance an allogeneic GVL effect would intuitively not have the same role as in standard recipient-derived relapses. There are also broader implications for donor selection and workup, particularly given the growing popularity of nonmyeloblative HSCT and corresponding rising age of the potential donor pool. Identification of DCL raises potential concerns over future health of the donor, posing ethical dilemmas regarding responsibilities toward donor notification (particularly in the context of cord blood transplantation). The entity of DCL is also of research interest, because it might provide a unique human model for studying the mechanisms of leukemogenesis in vivo. This review presents and collates all reported cases of DCL, and discusses the various strategies, controversies, and pitfalls when investigating origin of posttransplant relapse. Putative etiologic factors and mechanisms are proposed, and attempts made to address the difficult ethical questions posed by discovery of donor-derived malignancy within a HSCT recipient.

Bone marrow-derived stem cells and radiation response

The recovery of tissues and organs from ionizing irradiation is critically dependent on the repopulation of resident stem cells, defined as the subset of cells with capacity for both self-renewal and differentiation. Stem cells of both hematopoietic and epithelial origin reside in defined areas of the cellular microenvironment (recently defined as the stem cell "niche"). Experiments using serial repopulation assays in serial generations of total body irradiated mice receiving transplanted marrow and in continuous bone marrow cultures both identified specific microanatomic sites that comprise the bone marrow stem cell niche. Supportive cells of the hematopoietic microenvironment not only contribute to stem cell repopulation capacity but also to the maintenance of their quiescent or nonproliferative state, which allows the most primitive hematopoietic stem cells to stay in a noncycling state protected from both direct ionizing radiation-induced cell-cycle phase-specific killing and indirect cytokine and free radical mediated killing. Recent evidence has defined both cell contact and humoral mechanisms of protection of hematopoietic stem cells by stromal cells. There is also recent evidence for multilineage differentiation capacity of cells of the hematopoietic microenvironment termed bone marrow stromal cells (mesenchymal stem cells). Both hematopoietic stem cells and mesenchymal stem cell populations have been shown to be involved in the repair of ionizing irradiation damage of distant epithelial as well as other hematopoietic sites through their capacity to migrate through the circulation. The radiobiology of these 2 bone marrow stem cell populations is the subject of intense investigation. This review defines the status of research in the areas of stem cell quiescence, niche contact, and migratory responses to ionizing irradiation.

Long-term persistence of nonpathogenic clonal chromosome abnormalities in donor hematopoietic cells after allogeneic stem cell transplantation

We describe the cases of two unrelated patients who exhibited multiple chromosomal abnormalities in donor cells after allogeneic peripheral blood stem cell transplantation (PBSCT). The patients were diagnosed with chronic myeloid leukemia and chronic lymphocytic leukemia, respectively, and both underwent nonmyeloablative conditioning with cyclophosphamide and fludarabine followed by PBSCT from their HLA-matched opposite-sex siblings. Post-transplant bone marrow cytogenetics showed full engraftment, and the early post-transplant studies demonstrated only normal donor metaphases. Subsequent studies of both patients, however, revealed a population of metaphase cells with abnormal, but apparently balanced, donor karyotypes. Chromosome studies performed on peripheral blood cells collected from both donors after transplantation were normal. Both patients remained in clinical remission during follow-up of approximately 8 years in one case, and 6 years in the other case, despite the persistence of the abnormal clones. Chromosomal abnormalities in residual recipient cells after bone marrow or PBSCT are not unusual. In contrast, only rare reports of chromosome abnormalities in donor cells exist, all of which have been associated with post-bone marrow transplant myelodysplastic syndrome or acute leukemias. The present cases demonstrate the rare phenomenon of persistent clonal nonpathogenic chromosome aberrations in cells of donor origin.

Second malignancies after allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) may prolong life and cure patients suffering from otherwise fatal diseases. However, the growing population of long-term survivors has led to the realization of multiple long-term complications, including the risk of second malignancies. Compared to the autologous setting, allo-HCT carries a much higher risk of posttransplant lymphoproliferative disorder (PTLD), which usually occurs within the first year after allo-HCT and is strongly associated with the Epstein-Barr virus (EBV). Treatment-related myelodysplastic syndromes (tMDS) and second leukemias are extremely rare. Both autologous and allo-HCT carry increased risks for second solid malignancies (SSM). The cumulative incidence of SSM continues to increase in each of the largest studies with as much as 20 years of follow-up, likely related to the long latency of radiation-related SSM. Systematic, prospective monitoring, vigilant screening processes, and well-maintained survivorship clinics and databases are absolute necessities, and should be included in the infrastructure of individual transplant centers and networks, with mandatory periodic reporting of second malignancy incidences. Primary care and transplant physicians alike must be aware of the risk of second malignancies after allo-HCT. Most importantly, guidelines should be developed in regard to screening and prevention of second malignancies, so that physicians can provide state-of-the-art counsel and care for the benefit of our patients.

Donor cell leukemia: a critical review

Approximately 40 cases of DCL have been reported in the literature; cases have been reported after allografts from bone marrow, peripheral blood and cord blood. The study of these cases may provide new insights into the mechanisms of leukemogenesis. Some data suggest that the prevalence of this complication has been under-estimated. Most cases of DCL have occurred following transplantation for leukemia, but there have also been cases reported after transplantation for non-malignant conditions. Various mechanisms have been proposed to explain how DCL arise and are briefly discussed. Additional studies are needed to define with more detail both the true prevalence of this complication and its precise pathogenetic mechanism.

Donor derived malignancy following transplantation: a review

Organ and tissue transplant is now the treatment of choice for many end stage diseases. In the recent years, there has been an increasing demand for organs but not a similar increase in the supply leading to a severe shortage of organs for transplant resulted in increasing wait times for recipients. This has resulted in expanded donor criteria to include older donors and donors with mild disease. In spite of implementation of more stringent criteria for donor selection, there continues to be some risk of donor derived malignancy. Malignancy after transplantation can occur in three different ways: (a) de-novo occurrence, (b) recurrence of malignancy, and (c) donor-related malignancy. Donor related malignancy can be either due to direct transmission of tumor or due to tumor arising in cells of donor origin. We will review donor related malignancies following solid organ transplantation and hematopoeitic progenitor cell transplantation. Further, we will briefly review the methods for detection and management of these donor related malignancies.

Evidence of Donor-Derived Hematologic Malignancies after Hematopoietic Stem Cell Transplantation

Increasing the upper age limit for recipients of hematopoietic stem cell transplantation (HCT) naturally has also increased the age of the corresponding related donor population. Because aging is a risk factor for malignancies, the risk of transferring preexisting malignant or premalignant hemopoietic clones in the process of HCT might be expected to increase as well. Anecdotal clinical cases of malignancies derived from donor cells in patients undergoing HCT have been published since 1971. In this article, we report 12 new cases that fit 2 different categories: (1) cases in which clones with characteristics of lymphohemopoietic malignancies were transferred from the donors to the recipients and (2) cases in which the malignant clone evolved from healthy donor cells once transplanted into the recipient. Donors in the first group were significantly older than donors in the second group. A more systematic examination of the prevalence and biology of donor malignancies would merit study.

Donor cell leukemia developing after hematopoietic stem cell transplantation for multiple myeloma

The development of secondary leukemia in donor cells after allogeneic stem cell transplantation is a rare event. We describe the occurrence of acute myeloid leukemia in donor cells 4 years after a stem cell transplantation for multiple myeloma. The multiple myeloma was relapsing at the time of the onset of acute myeloid leukemia. Secondary leukemia in donor cells after transplantation for multiple myeloma has not yet been reported.

Acute myeloid leukemia of donor origin after allogeneic bone marrow transplantation for precursor T-cell acute lymphoblastic leukemia: case report and review of the literature

We report a case of donor-derived acute myeloid leukemia (AML) occurring in a 33-year-old man after allogeneic bone marrow transplantation (BMT) for precursor T-cell acute lymphoblastic -leukemia (T-ALL). The cells for BMT were from his human leukocyte antigen (HLA)-matched sister. Fluorescence in-situ hybridization (FISH) analysis showed the AML to be of donor origin (i.e., karyotypically female) with an 11q23 (mixed lineage leukemia (MLL) gene) translocation, while the original T-ALL exhibited a male karyotype with abnormalities of chromosomes 6, 8, and a t(10;14)(q24;q11.2). Subsequent molecular short tandem repeat studies confirmed the AML to be of donor origin. Donor-cell leukemia (DCL) after allogeneic BMT is a rare, yet well-documented, event. Our report presents clinicopathologic information about a case of DCL and a review of the recent literature.

Acute leukemia of donor origin arising after stem cell transplantation for acute promyelocytic leukemia

We report a patient with PML/RARalpha-positive acute promyelocytic leukemia (APL) who developed PML/RARalpha-negative acute myeloid leukemia 37 months after allogeneic bone marrow (BMT) transplant for molecular relapse. Features of myelodysplasia were noted 11 months earlier, chimerism testing by analysis of short tandem repeats was consistent with development of myelodysplasia and acute leukemia within cells of donor origin. To our knowledge, this is the first report of donor cell leukemia following BMT for APL. We hypothesize that replicative stress may lead to the development of some cases of donor cell acute leukemia.

B-cell lymphoma developing in the donor 9 years after donor-origin acute myeloid leukemia post bone marrow transplantation

Donor-cell leukemia post bone marrow transplantation is a rare event. Most of the cases reported to date have developed in cells from an HLA-matched sibling, who had no evidence of malignant disease before or following the occurrence of donor-origin leukemia. We describe a 17-year-old female who developed B-cell lymphoma 9 years following the occurrence of donor-origin acute myeloid leukemia in her brother for whom she had donated marrow. Cytogenetic analysis of the tumor revealed multiple chromosomal aberrations. The donor was heterozygous for the Ashkenazi mutation of Bloom's syndrome, suggesting that donor-type leukemia could have resulted from genomic instability in the donor cells.

Sickle cell anemia and hematological neoplasias

Sickle cell disease (SCD) is a congenital hemolytic anemia with various clinical findings. In some cases hematological neoplasias and some solid tumors may accompany this disease but these have rarely been reported. Here we report five cases with SCD and accompanying hematological neoplasias including lymphoblastic lymphoma, multiple myeloma and hairy cell leukemia in four cases with sickle cell trait and one case of Hodgkin' disease in sickle cell anemia. All of the cases except one had no previously diagnosed congenital hemolytic anemia and/or family history. Peripheral blood findings suggestive for an underlying hemolytic anemia were the first step and the most important initial lead in the detection of SCD. Severe musculoskeletal signs during the first presentation was seen in the lymphoma case, residual renal dysfunction after remission of multiple myeloma, and areas of infarction in the spleen in CT scans in the patient with sickle cell anemia were the most interesting findings in these cases. A standard therapeutic approach without any additional toxicity was relevant in all cases. Detailed clinical presentation and outcome of these five cases are documented here and the literature has been reviewed.

Acute myeloid leukaemia of donor cell origin developing 5 years after allogeneic bone marrow transplantation for chronic myeloid leukaemia

We report the case of a male patient with Ph-positive CML who developed AML 5 years after allogeneic BMT. Clinically, the AML seemed to develop on the basis of a myelodysplasia. The myeloid origin of blasts has been proven by immunophenotyping. The variable number of tandem repeats (VNTRs) and short tandem repeat (STR) showed donor-type haemopoiesis. The interphase FISH showed the XX genotype directly in the morphologically identifiable blasts and in the CD34-positive sorted bone marrow cells. This proved the new leukaemia to be of donor origin. The necessity of using multiple techniques and the advantage of combined immunophenotyping and FISH methods in this case is emphasized.

Leukaemic transformation of donor cells in a patient receiving a second allogeneic bone marrow transplant for severe aplastic anaemia

Allogeneic blood or bone marrow transplantation is a successful treatment for leukaemia and severe aplastic anaemia (SAA). Graft rejection following transplantation for leukaemia is a rare event but leukaemic relapse may occur at varying rates, depending upon the stage of leukaemia at which the transplant was undertaken and the type of leukaemia. Relapse is generally assumed to occur in residual host cells, which are refractory to, or escape from the myeloablative conditioning therapy. Rare cases have been described, however, in which the leukaemia recurs in cells of donor origin. Lack of a successful outcome of blood or bone marrow transplantation for severe aplastic anaemia (SAA), however, is due to late graft rejection or graft-versus-host disease. Leukaemia in cells of donor origin has rarely been reported in patients following allogeneic bone marrow transplantation for SAA. This report describes leukaemic transformation in donor cells following a second allogeneic BMT for severe aplastic anaemia. PCR of short tandem repeats in bone marrow aspirates and in colonies derived from BFUE and CFU-GM indicated the donor origin of leukaemia. Donor leukaemia is a rare event following transplantation for severe aplastic anaemia but may represent the persistence or perturbation of a stromal defect in these patients inducing leukaemic change in donor haemopoietic stem cells.

Donor cell leukemia: report of a case occurring 11 years after allogeneic bone marrow transplantation and review of the literature

We report the case of a man with chronic myelocytic leukemia (CML) and a 46,XY,t(5;9;22) karyotype who developed acute myelocytic leukemia (AML) with a 45,X,t(8;21) karyotype 11 years after bone marrow transplantation (BMT) from his HLA-matched sister. Fluorescent in situ hybridization (FISH) studies and molecular analysis using short tandem repeat (STR) sequences proved the new leukemia to be of donor cell origin. Donor cell leukemia (DCL) after BMT is rare. Our review of the literature found 15 cases following BMT for leukemia and 2 cases after BMT for benign hematological disorders. In fewer than half the reported cases were molecular studies available to confirm the cytogenetic evidence for DCL, and the longest previously reported interval between BMT and DCL was 6 years.

Acquired monosomy 7 in donor cells in a patient treated for acute lymphoblastic leukemia with bone marrow transplantation

Two years after a bone marrow transplant (BMT) from his haploidentical mother, a 28-year-old male with a history of acute lymphoblastic leukemia (ALI.) developed myelodysplastic syndrome (MDS) with monosomy 7 in his female bone marrow cells. Follow-up cytogenetic studies, including fluorescence in situ hybridization (FISH) performed twenty-seven and thirty-one months post-BMT consistently showed a female chromosome pattern with monosomy 7. Thirty-six and thirty-nine months post-BMT, further clonal evolution occurred, with the appearance of a sideline of the female cells that first expressed a del(10)(p11.2) and then developed a translocation, t(10;21)(p11.2;q22), in addition to the monosomy 7. Cytogenetic monitoring of this male patient helped to reveal a rare case of early MDS in transplanted donor cells and evolution of the acquired abnormal clone by identifying chromosomal alterations in the donated female bone marrow cells.

Trisomy X in a female member of a family with X linked severe combined immunodeficiency: implications for carrier diagnosis

We describe a family affected by X linked severe combined immunodeficiency (SCIDX1) in which genetic prediction of carrier status was made using X chromosome inactivation studies together with limited genetic linkage analysis. Linkage studies in this family showed a confusing pattern of inheritance for the X chromosome. A female with a random pattern of X chromosome inactivation in her T cells appeared to have inherited an X chromosome with four recombinations within 10 cM. The odds of this happening in a single meiotic event make this an unlikely explanation. Data obtained from studying the X chromosomes of her two unaffected sons showed that this could be explained simply on the basis of her having inherited three alleles each of the relevant polymorphic DNA loci. We used fluorescent in situ hybridisation (FISH) to confirm that this person had inherited three complete X chromosomes. Thus, although the results from X chromosome inactivation analysis indicated that this subject was not a carrier of the affected chromosome, FISH and genetic linkage analysis showed clearly that the affected chromosome had been inherited. The implications of this finding for diagnosis of carrier status in this family and for other families with X linked inherited immunodeficiencies is discussed.

New methods in cytogenetics

Developments in the technique of fluorescence in situ hybridization (FISH) now permit hybridization of sequences ranging from 1 kb to whole genomes. The technique can be used in applications from coarse mapping of whole chromosomes to high-resolution analysis of extended strands of DNA. The complexity, and hence the coverage, of 'paints' prepared by amplification is being improved to the extent that such methods are used in cloning strategies for the generation of region-specific probes. Interphase analysis and comparative genomic hybridization are becoming important tools in cancer cytogenetics, and the potential for routine analysis of fetal cells obtained from maternal blood may provide a fresh approach to prenatal cytogenetic screening. Functional studies of gene activity and nuclear organization are now also possible.

A case of myelodysplasia with eosinophilia having a translocation t(5;12) (q31;q13) restricted to myeloid cells but not involving eosinophils

A chromosomally abnormal clone characterized by a translocation, t(5;12)(q31;q13), was detected in the marrow of a child with myelodysplasia and associated eosinophilia which included a generalized skin infiltration. Combined immunophenotyping and fluorescence in situ hybridization on interphase bone marrow cells showed that the chromosomal rearrangement was restricted to the granulocyte lineage but was not present in the eosinophils. If the chromosome rearrangement is important in the overproduction of eosinophils in this case, the lineage restriction found suggests that its effect must be indirect.