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* Emma Childrens Hospital
Department of Clinical Genetics, Institute for Human Genetics, Academic Medical Center, Amsterdam, Netherlands
Leiden University Medical Center, Leiden, Netherlands
| ABSTRACT |
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CT [K62X] and IVS2(258)+2T
C [C84fs]) were found. Results. Bone marrow transplantation from a matched unrelated donor was unsuccessful. The genetic information from the deceased patient enabled us to perform prenatal molecular studies during the subsequent pregnancy, successfully predicting a nonaffected child.
Conclusions. This report describes for the first time the hematologic abnormalities of congenital aplastic anemia and prolonged neonatal hypoglycemia as the presenting symptoms of Shwachman-Diamond syndrome. The finding of common mutations in the presence of these symptoms at birth suggests the lack of a clear phenotype-genotype relationship in this syndrome.
Key Words: aplastic anemia hematology genotype congenital bone marrow transplantation
Abbreviations: SDS, Shwachman-Diamond syndrome CHH, cartilage/hair hypoplasia DKC, dyskeratosis congenita G-CSF, granulocyte colony-stimulating factor BM, bone marrow BMT, bone marrow transplantation PCR, polymerase chain reaction
Shwachman-Diamond syndrome (SDS) (Online Mendelian Inheritance in Man no. 260400) is a rare autosomal recessive disorder that usually manifests itself in infancy or early childhood. The disease is extremely heterogeneous, showing a wide variety of abnormalities and symptoms. It is characterized mainly by exocrine pancreatic insufficiency, short stature, and bone marrow (BM) dysfunction.13 Several studies have shown that, with advancing age, 40% to 60% of patients exhibit pancreatic sufficiency. Elevated liver enzyme levels and hepatomegaly have been observed in the first years of life, with subsequent improvement without complications (similar to the pancreatic insufficiency).3 Intermittent neutropenia is the most common hematologic finding in SDS. Hematologic manifestations other than neutropenia include anemia, increased fetal hemoglobin levels, thrombocytopenia, and aplastic anemia.2,4,5 As with other constitutional BM failure syndromes, there is a tendency toward malignant myeloid transformation. Recombinant human granulocyte colony-stimulating factor (G-CSF) has been used for some SDS subjects with severe neutropenia but is not recommended because of the risk of acute myeloid leukemia, although the exact prevalence of the disease and its induction by G-CSF are difficult to establish.2
Growth retardation is a typical manifestation. Weight and length are deficient at birth and remain below normal with time. Some patients with SDS present with short stature only, rather than malnutrition or malabsorption, which suggests an inherent growth problem. A broad spectrum of skeletal abnormalities, including metaphyseal dysostosis and epiphyseal dysplasia, has been found to be associated with this syndrome. Additional clinical features include immune dysfunction, liver disease, renal tubular defects, insulin-dependent diabetes mellitus, and psychomotor retardation.6,7
No unifying pathogenic mechanism has yet been shown to be responsible for SDS, although the genetic basis of this rare disease was recently described.8 Indirect lines of evidence indicate that the orthologs may function in RNA metabolism. YLR022c has been clustered with genes encoding RNA-processing enzymes.9 Restriction digestion or sequencing of polymerase chain reaction (PCR) products from affected individuals showed that
75% of alleles associated with SDS were the result of gene conversion, which was confined to a short segment with a maximal size of 240 base pairs. Approximately 90% of affected individuals carry at least 1 converted allele, and 60% carry 2 converted alleles. Alleles from affected individuals without conversion mutations had other changes in the coding region of SBDS, which led to frameshift and missense changes.8 We present an unusual case of congenital aplastic anemia combined with transient hypoglycemia during early infancy with a diagnosis of SDS, which was confirmed by the identification of 2 common mutations in the SBDS gene.
| METHODS |
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Histochemical Analyses
Histochemical and immunophenotypic analyses of the liver and muscle were conducted with standard staining procedures, with a streptavidin-biotin complex method for paraffin-embedded sections and a 3-step, indirect, immunoperoxidase method, with 3-amino-9-ethylcarbazole as a substrate, for frozen sections. Electron microscopy was performed with the tissue samples simultaneously, with Karnovsky embedding.
Molecular Studies
Genomic DNA from peripheral mononuclear cells and fibroblasts from the patient were extracted with standard methods. The SBDS gene was amplified in separate PCRs with primer sets identical to those described by Boocock et al,8 with essentially the same genomic PCR conditions as described. Direct sequencing was performed with an ABI PRISM Big Dye terminator v1.1 cycle sequencing kit (Applied Biosystems, Foster City, CA), and PCR products were separated in 1% SeaKem (FMC BioProducts, Rockland, ME) gels, purified with a Qiagen gel extraction kit (Qiagen, Hildena, Germany), and sequenced automatically (ABI3100 sequencer; Applied Biosystems).
| CLINICAL REPORT |
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8 weeks. Ultrasonographic evaluations of the head yielded normal results. Echocardiography showed nonclosure of the foramen ovale, with moderate left-to-right shunting. The pulmonary artery pressure was 35 mm Hg. Microbiologic cultures all yielded negative results. Serologic tests for congenital infections yielded negative results, as did PCR tests for cytomegalovirus, parvovirus B19, herpes simplex virus, and Epstein-Barr virus. The patient experienced persistent periods of unexplained hypoglycemia, with transient lactate acidemia (peak: 5.4 mmol/L). She was extensively evaluated for metabolic disorders, in particular mitochondrial disorders, but no clues were found in a liver biopsy, muscle biopsy, and mitochondrial DNA analysis. The patient was treated with decreasing amounts of diazoxide until glucose levels were completely normalized. Fanconi anemia was considered because of the aplastic anemia (Fig 1) but was excluded because of normal mitomycin C test results. Neonatal lupus was excluded because of the absence of autoantibodies in the mother and the newborn. Thrombopoietin levels were strongly increased (786 kU/L; normal: <40 kU/L); the absence of mutations in the MPL gene made severe congenital amegakaryocytic thrombocytopenia unlikely. Moreover, plasma levels of folic acid and vitamin B12 were normal; ferritin levels increased within the first 3 months, from 24 to 890 µg/L, after 4 erythrocyte transfusions. Chromosomal analysis indicated a normal female pattern (46, XX).
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Examination at admission showed a pale dystrophic girl, with weight of 6980 g (<3 SD) and height of 68 cm (<3 SD). The tonsils were present, and the lymph nodes were not enlarged. There was hepatomegaly but no enlargement of the spleen. The patient had no clinical jaundice. No proof of a recent (viral) infection was obtained. The BM was hypocellular, without much erythropoiesis. The myeloid lineage was hypoplastic; megakaryocytes were not detected. Clonal derangements and myelodysplasia were excluded on the basis of morphologic, immunophenotyping, and cytogenetic studies (eg, monosomy 7 or i7q).
Immunologic studies indicated no defects. Lymphocyte proliferation tests yielded largely normal results with activation with mitogens or combined CD3/CD28 receptor signaling (data not shown). A normal-sized thymus was observed with computed tomography; no lung abnormalities or scarring was observed. Echocardiography showed normal anatomic dimensions and good ventricular contractions, with normal fractional shortening for age. Liver and kidney functions were normal at that time. Microbiologic cultures and PCR tests yielded negative results for several viruses (ie, all herpes viruses, human immunodeficiency virus, and parvovirus B19) in nose washings, feces, urine, and/or blood.
The patient received 2.5 x 108 nucleated cells per kg. Graft-versus-host disease prophylaxis consisted of methotrexate and cyclosporine A. Posttransplantation supportive care consisted of total gastrointestinal decontamination in a strict protective (sterile) environment. Hematologic engraftment failed. On the 30th day after BMT, circulatory insufficiency became evident during Escherichia coli sepsis. A second infusion of donor BM was performed on the 47th day. Thereafter, the patient experienced clinical gastroenteritis and a systemic adenovirus infection that worsened her condition, with rapidly increasing viral DNA concentrations. She died on the 69th day, as a result of multiple-organ failure.
Sequence analysis showed that the patient was compound heterozygous for 2 common mutations in exon 2 of the SBDS gene (Fig 3). These mutations were previously identified among SDS patients.7 Analysis of SBDS genomic sequences in each of the parents confirmed the presence of the genetic changes in the heterozygous condition, ie, 183-184TA
CT, resulting in a stop codon (K62X), in the mother and IVS2(258)+2T
C, leading to a C84 frameshift splicing event, in the father.
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C (C84fs) mutation only, and a healthy boy was born. | DISCUSSION |
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The presentation of SDS for our patient was highly unusual. The SBDS gene product is presumed to function in RNA processing. This function and its clinical implications are reminiscent of those of the RMRP gene, which, when defective, causes cartilage/hair hypoplasia (CHH) and impairs hematologic and immunologic functions.8,19,20 However, the growth failure in SDS is proportional and differs from the disproportional growth in CHH. Moreover, the exocrine pancreas insufficiency is most typical for SDS, whereas Hirschsprung disease may coincide with CHH.2,14 Dyskeratosis congenita (DKC) also is caused by a defect in RNA processing.21,22 The defective protein, dyskerin, in X-linked DKC is associated not only with H/ACA small nucleolar RNA but also with human telomerase RNA, which was found to be defective in autosomal DKC.23 Telomerase adds simple sequence repeats to chromosome ends by using an internal region of its RNA as a template. Interestingly, shortened telomeres have been demonstrated in the leukocytes of patients with SDS,20,24 although it remains to be shown whether this results from defective telomerase activity or hyperproliferation.
Overt BM failure at birth has never been observed in SDS, although aplastic anemia, with transfusion dependence, has been noted at older ages during childhood and adolescence.5,6 In contrast to our case, the symptoms of pancreatic insufficiency are suggested to be most prominent in SDS at the time of diagnosis and especially during infancy, although they resolve with time for >50% of patients.13 In our case, the diagnosis of SDS was finally established at the age of 6 months, because of the combined hematologic abnormalities, growth failure with metaphyseal dysplasia, mild hepatitis, and fat malabsorption, with undetectable elastase and chymotrypsin in the feces. The BM failure reacted marginally to the addition of growth factors such as erythropoietin and G-CSF.
Although BMT or hematopoietic stem cell transplantation has been attempted for treatment of the hematologic disturbances of SDS, few survivors have been reported to date.2528 Poor outcomes are often related to excessive cardiac and other organ toxicity resulting from the conditioning regimen before transplantation and a stromal cell defect that is part of the syndrome.
| CONCLUSIONS |
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Taken together with the findings of Boocock et al,8 the common mutations in the present case and our analysis of 10 additional SDS cases (T.W. Kuijpers, M. Alders, and R.C.M. Hennekam, unpublished observations) suggest that a clear genotype-phenotype relationship may not exist in SDS. This would be in agreement with the lack of concordance in hematologic findings among affected siblings and the wide variability within families.3
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Reprint requests to (T.W.K.) Emma Childrens Hospital, Academic Medical Center (G8-205), Meibergdreef 9, 1105 AZ Amsterdam, Netherlands. E-mail: t.w.kuijpers{at}amc.uva.nl
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T. W. Kuijpers, M. Alders, A. T. J. Tool, C. Mellink, D. Roos, and R. C. M. Hennekam Hematologic abnormalities in Shwachman Diamond syndrome: lack of genotype-phenotype relationship Blood, July 1, 2005; 106(1): 356 - 361. [Abstract] [Full Text] [PDF] |
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