Totipotent stem cells bearing del(20q) maintain multipotential differentiation in Shwachman Diamond syndrome

Case Report: Refractory Cytopenia With a Switch From a Transient Monosomy 7 to a Disease-Ameliorating del(20q) in a NHEJ1-Deficient Long-term Survivor

We report the case of a male Pakistani patient with a pathogenic homozygous loss of function variant in the non-homologous end-joining factor 1 (NHEJ1) gene. The growth retarded and microcephalic boy with clinodactyly of both hands and hyperpigmentation of the skin suffered from recurrent respiratory infections. He was five and a half years old when he came to our attention with refractory cytopenia and monosomy 7. Hematopoietic stem cell transplantation was considered but not feasible because there was no suitable donor available. Monosomy 7 was not detected anymore in subsequent bone marrow biopsies that were repeated in yearly intervals. Instead, seven and a half years later, a novel clone with a del(20q) appeared and steadily increased thereafter. In parallel, the patient’s blood count, which had remained stable for over 20 years without necessitating any specific therapeutic interventions, improved gradually and the erythropoiesis-associated dysplasia resolved.

Lessons From Pediatric MDS: Approaches to Germline Predisposition to Hematologic Malignancies

Pediatric myelodysplastic syndromes (MDS) often raise concern for an underlying germline predisposition to hematologic malignancies, referred to as germline predisposition herein. With the availability of genetic testing, it is now clear that syndromic features may be lacking in patients with germline predisposition. Many genetic lesions underlying germline predisposition may also be mutated somatically in de novo MDS and leukemias, making it critical to distinguish their germline origin. The verification of a suspected germline predisposition informs therapeutic considerations, guides monitoring pre- and post-treatment, and allows for family counseling. Presentation of MDS due to germline predisposition is not limited to children and spans a wide age range. In fact, the risk of MDS may increase with age in many germline predisposition conditions and can present in adults who lack classical stigmata in their childhood. Furthermore, germline predisposition associated with DDX41 mutations presents with older adult-onset MDS. Although a higher proportion of pediatric patients with MDS will have a germline predisposition, the greater number of MDS diagnoses in adult patients may result in a larger overall number of those with an underlying germline predisposition. In this review, we present a framework for the evaluation of germline predisposition to MDS across all ages. We discuss characteristics of personal and family history, clinical exam and laboratory findings, and integration of genetic sequencing results to assist in the diagnostic evaluation. We address the implications of a diagnosis of germline predisposition for the individual, for their care after MDS therapy, and for family members. Studies on MDS with germline predisposition have provided unique insights into the pathogenesis of hematologic malignancies and mechanisms of somatic genetic rescue vs. disease progression. Increasing recognition in adult patients will inform medical management and may provide potential opportunities for the prevention or interception of malignancy.

Somatic genetic rescue in hematopoietic cells in GATA2 deficiency

Haploinsufficiency of GATA2 caused by heterozygous loss-of-function mutations is associated with cytopenias and predisposition to myelodysplasia and AML with other variable extrahematopoietic manifestions, including lymphedema, pulmonary alveolar proteinosis, and hearing loss. The authors report on 2 siblings with the disorder whose father was asymptomatic because of an acquired missense mutation in the affected allele that was restricted to hematopoietic cells; surprisingly, he also had no extrahematopoietic complications.

Clonal hematopoiesis in the inherited bone marrow failure syndromes

Inherited bone marrow failure syndromes (IBMFSs) are characterized by ineffective hematopoiesis and increased risk for developing myeloid malignancy. The pathophysiologies of different IBMFSs are variable and can relate to defects in diverse biological processes, including DNA damage repair (Fanconi anemia), telomere maintenance (dyskeratosis congenita), and ribosome biogenesis (Diamond-Blackfan anemia, Shwachman-Diamond syndrome). Somatic mutations leading to clonal hematopoiesis have been described in IBMFSs, but the distinct mechanisms by which mutations drive clonal advantage in each disease and their associations with leukemia risk are not well understood. Clinical observations and laboratory models of IBMFSs suggest that the germline deficiencies establish a qualitatively impaired functional state at baseline. In this context, somatic alterations can promote clonal hematopoiesis by improving the competitive fitness of specific hematopoietic stem cell clones. Some somatic alterations relieve baseline fitness constraints by normalizing the underlying germline deficit through direct reversion or indirect compensation, whereas others do so by subverting senescence or tumor-suppressor pathways. Clones with normalizing somatic mutations may have limited transformation potential that is due to retention of functionally intact fitness-sensing and tumor-suppressor pathways, whereas those with mutations that impair cellular elimination may have increased risk for malignant transformation that is due to subversion of tumor-suppressor pathways. Because clonal hematopoiesis is not deterministic of malignant transformation, rational surveillance strategies will depend on the ability to prospectively identify specific clones with increased leukemic potential. We describe a framework by which an understanding of the processes that promote clonal hematopoiesis in IBMFSs may inform clinical surveillance strategies.

The Greek Registry of Shwachman Diamond-Syndrome: Molecular and clinical data

This study presents the clinical phenotype and molecular analysis findings from 11 patients recorded in the Greek Shwachman-Diamond syndrome (SDS) Registry. The most severely affected patient in our registry was diagnosed at birth and is the first patient reported to require bone marrow transplantation so early in life. Severe psoriasis, a feature not previously reported in SDS, was observed in one patient. Mutations in the Shwachman-Bodian-Diamond syndrome gene (SBDS) were found in all patients. Cytogenetic analyses revealed clonal abnormalities, one novel, in two patients.

Mosaic chromosome 20q deletions are more frequent in the aging population

Deletions on the long-arm of chromosome 20, del(20q), are common karyotypic abnormalities in myeloid disorders. Bioinformatic analyses of the B-allele frequency and log R ratio values from genome-wide association data have identified individuals who are mosaic for large structural abnormalities (>2 Mb). We investigated the most common autosomal event, namely mosaic del(20q), in 46 254 nonhematologic cancer cases and 36 229 cancer-free controls. We detected 91 mosaic del(20q) in leukocytes (80%) and buccal material (20%). The mosaic del(20q) mapped to a well-characterized minimally deleted region (MDR) reported in myeloid disorders. Common breakpoint clusters map to the coordinates of 29.9 to 31.5 Mb on the centromeric side of mosaic del(20q), and 42.0 to 45.4 Mb and 48.1 to 50.7 Mb on the telomeric end (GRCh36). Multivariate analyses suggest del(20q) increases with age, and is more common in males but less common in individuals of African ancestry. No conclusive associations were noted between the presence of mosaic del(20q) and subsequent solid tumor risk. Our observations demonstrate that the MDR of del(20q) is the most common large scale mosaic autosomal abnormality in whole blood and has a frequency of ∼1 in every 1000 adults over the age of 50, which exceeds the expected incidence of myeloid leukemia in the population. Our results indicate that subclonal mosaic events of a region implicated in myeloid disorders on 20q are more frequent than the predicted population-estimated incidence of myeloid diseases, and thus suggest that these events can be tolerated until additional events accumulate that drive myeloid disorders.

Cytogenetic monitoring in Shwachman-Diamond syndrome: a note on clonal progression and a practical warning

We analyzed the results of periodic chromosome analyses performed on bone marrow of 22 patients with Shwachman-Diamond syndrome (SDS), 8 directly observed and 14 from the literature, selected because of changes in the cytogenetic picture during the course of the disease. This study points out some features of the cytogenetic evolution in SDS relevant for prognostic evaluation but never noted in the literature. In particular, the lack of any clonal progression and the frequent appearance of independent clones with chromosomal changes different from the one initially discovered, with possible severe prognostic implications, are reported.

Clinical spectrum and molecular pathophysiology of Shwachman-Diamond syndrome

PURPOSE OF REVIEW

Shwachman-Diamond syndrome (SDS) is an inherited bone marrow failure and cancer predisposition syndrome that affects multiple organ systems. Mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene are found in the majority of patients, but the molecular function of the SBDS protein product remains unclear. In this article, we review recent progress in the clinical and molecular characterization of SDS.

RECENT FINDINGS

Emerging data support a multifunctional role for the SBDS protein. Current studies indicate that SBDS functions in 60S large ribosomal subunit maturation and in mitotic spindle stabilization. Recent data suggest that it may also affect actin polymerization, vacuolar pH regulation, and DNA metabolism. SBDS loss results in both hematopoietic cell-intrinsic defects as well as marrow stromal abnormalities.

SUMMARY

SDS is a multisystemic disease arising from defects in a protein that participates in several essential cellular processes. Elucidating the molecular function of SBDS will provide important insights into how defects in ribosome biogenesis and mitotic spindle stabilization result in hematopoietic failure, cancer predisposition, and abnormalities.

Deletion(20q) as the sole abnormality in plasma cell myeloma is not associated with plasma cells as identified by cIg FISH

Deletion of 20q is a common finding in myeloid disorders but it is also observed in plasma cell myeloma (PCM). As a del(20q) in a patient receiving treatment for myeloma may indicate therapy-related myelodysplastic syndrome (t-MDS), it is important to differentiate chromosome abnormalities associated with myeloma from those reflecting t-MDS. We performed fluorescence in situ hybridization (FISH) using a 20q12 probe (D20S108) in conjunction with cytoplasmic immunoglobulin (cIg) staining in 20 PCM cases with a del(20q) in order to confirm the cell type involved. Of the nine cases studied with a clone showing a del(20q) as the sole abnormality, 8 of 9 demonstrated loss of the D20S108 signals in non-plasma cells only and 5 of 9 had either a confirmed myeloid malignancy in addition to PCM or showed evidence of dysplastic changes in the marrow; however, of the 11 patients with a del(20q) within a complex PCM karyotype, 4 of 11 showed loss of the D20S108 signals in plasma cells only and 7 of 11 showed no significant loss in either plasma cells or non-plasma cells. Therefore, our results indicate that a del(20q) as the sole abnormality in PCM is present in non-plasma cells and, therefore, suggests the presence of an associated myeloid malignancy.

Clinical and molecular pathophysiology of Shwachman-Diamond syndrome: an update

Shwachman-Diamond syndrome (SDS) is an inherited neutropenia syndrome associated with a significant risk of aplastic anemia and malignant transformation. Multiple additional organ systems, including the pancreas, liver, and skeletal and central nervous systems, are affected. Mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene are present in most patients. There is growing evidence that SBDS functions in ribosomal biogenesis and other cellular processes. This article summarizes the clinical phenotype of SDS, diagnostic and treatment approaches, and novel advances in our understanding of the molecular pathophysiology of this disease.

The route to development of myelodysplastic syndrome/acute myeloid leukaemia in Shwachman-Diamond syndrome: the role of ageing, karyotype instability, and acquired chromosome anomalies

An investigation of 22 new patients with Shwachman-Diamond syndrome (SDS) and the follow-up of 14 previously reported cases showed that (i) clonal chromosome changes of chromosomes 7 and 20 were present in the bone marrow (BM) of 16 out of 36 cases, but if non-clonal changes were taken into account, the frequency of anomalies affecting these chromosomes was 20/36: a specific SDS karyotype instability was thus confirmed; (ii) the recurrent isochromosome i(7)(q10) did not include short arm material, whereas it retained two arrays of D7Z1 alphoid sequences; (iii) the deletion del(20)(q11) involved the minimal region of deletion typical of myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML); (iv) only one patient developed MDS, during the rapid expansion of a BM clone with a chromosome 7 carrying additional material on the short arms; (v) the acquisition of BM clonal chromosome anomalies was age-related. We conclude that karyotype instability is part of the natural history of SDS through a specific mutator effect, linked to lacking SBDS protein, with consequent clonal anomalies of chromosomes 7 and 20 in BM, which may eventually promote MDS/AML with the patients' ageing.