Segregation Analysis in Shwachman-Diamond Syndrome: Evidence for Recessive Inheritance

Shwachman-Diamond syndrome (SDS) results from mutations in the SBDS gene, characterized by exocrine pancreatic insufficiency and hematologic and skeletal abnormalities. Neutropenia and neutrophil dysfunction are hallmark features of SDS; however, causes for the bone defects are unknown. Dysfunction of boneresorbing osteoclasts, formed by the fusion of monocytic progenitors derived from the same granulocytic precursors as neutrophils, could be responsible. We report that Sbds is required for in vitro and in vivo osteoclastogenesis (OCG).Sbds-null murine monocytes formed osteoclasts of reduced number and size because of impaired migration and fusion required for OCG. Phenotypically, Sbdsnull mice exhibited low-turnover osteoporosis consistent with findings in SDS patients. Western blotting of Rho GTPases that control actin dynamics and migration showed a 5-fold decrease in Rac2, whereas Rac1, Cdc42, and RhoA were unchanged or only mildly reduced. Although migration was rescued on Rac2 supplementation, OCG was not. This was attributed to impaired signaling downstream of receptor activator of nuclear factor-B (RANK) and reduced expression of the RANK-ligand-dependent fusion receptor DC-STAMP. We conclude that Sbds is required for OCG by regulating monocyte migration via Rac2 and osteoclast differentiation signaling downstream of RANK. Impaired osteoclast formation could disrupt bone homeostasis, resulting in skeletal abnormalities seen in SDS patients. (Blood. 2011;117(6): 2044-2053) IntroductionShwachman-Diamond syndrome (SDS) is an autosomal recessive disorder with hallmark features of bone marrow failure, exocrine pancreatic insufficiency, and skeletal abnormalities. [1][2][3] Neutropenia is the most common clinical manifestation of bone marrow failure, but patients may also experience pancytopenia, anemia, and thrombocytopenia, and be at increased risk of developing aplastic anemia and acute myeloid leukemia. 4 In early crosssectional studies, metaphyseal dysostosis was observed in 40% to 80% of SDS patients, and rib and/or thoracic cage abnormalities in 30% to 50% of SDS patients. [5][6][7] More recently, in a longitudinal study, all of the SDS patients studied displayed various skeletal abnormalities, including delayed appearance of secondary ossification centers, variable widening, and irregularity of the metaphyses in early childhood followed by progressive thickening and irregularity of the growth plates, and generalized osteopenia. 8 In addition, a subset of patients showed early signs of osteoporotic vertebral deformities and disturbances in bone homeostasis manifesting in low-turnover osteoporosis. 8,9 Oral and dental diseases and conditions, including periodontitis, delayed eruption of the permanent dentition, increased caries risk in primary and permanent dentitions, and increased soft tissue pathoses, have also been reported. 10 SDS results from mutations in the ubiquitously expressed, conserved Shwachman-Bedian-Diamond syndrome gene (SBDS). 11 The exact function of the SBDS protein remains unclear; h...

Section: Introductionmentioning

confidence: 99%

Sbds is required for Rac2-mediated monocyte migration and signaling downstream of RANK during osteoclastogenesis

Leung

Cuddy

Wang

et al. 2011

“…Shwachman-Diamond syndrome (SDS) 1,2 is an autosomal recessive disease 3 characterized by exocrine pancreatic insufficiency, bone marrow failure, and leukemia predisposition (reviewed in Dror and Freedman 4 and Smith 5 ). Additional features commonly associated with this syndrome include skeletal malformations, 6 liver abnormalities, and short stature.…”

Section: Introductionmentioning

confidence: 99%

The Shwachman-Diamond SBDS protein localizes to the nucleolus

Austin

Leary

Shimamura

2005

119

117

Shwachman-Diamond syndrome (SDS) is an autosomal recessively inherited disorder characterized by exocrine pancreatic insufficiency and bone marrow failure. The gene for this syndrome, SBDS, encodes a highly conserved novel protein. We characterized Shwachman-Bodian-Diamond syndrome (SBDS) protein expression and intracellular localization in 7 patients with SDS and healthy controls. As predicted by gene mutation, 4 patients with SDS exhibited no detectable full-length SBDS protein. Patient DF277, who was homozygous for the IVS2 + 2 T>C splice donor mutation, expressed scant levels of SBDS protein. Patient SD101 expressed low levels of SBDS protein harboring an R169C missense mutation. Patient DF269, who carried no detectable gene mutations, expressed wild-type levels of SBDS protein to add further support to the growing body of evidence for additional gene(s) that might contribute to the pathogenesis of the disease phenotype. The SBDS protein was detected in both the nucleus and the cytoplasm of normal control fibroblasts, but was particularly concentrated within the nucleolus. SBDS localization was cell-cycle dependent, with nucleolar localization during G1 and G2 and diffuse nuclear localization during S phase. SBDS nucleolar localization was intact in SD101 and DF269. The intranucleolar localization of SBDS provides further supportive evidence for its postulated role in rRNA processing.

“…[6][7][8] SDS is inherited in an autosomal recessive fashion. 9 Recently, Boocock et al 10 reported that compound heterozygous mutations of the SBDS (Shwachman-Bodian-Diamond syndrome) gene on chromosome 7 were present in the majority of patients with SDS. Most of these mutations resulted from gene conversion with a neighboring pseudogene (SBDSP).…”

Section: Introductionmentioning

confidence: 99%

Mutations of the SBDS gene are present in most patients with Shwachman-Diamond syndrome

Woloszynek

Rothbaum

Rawls

et al. 2004

109

Shwachman-Diamond Syndrome (SDS) is a rare multisystem disorder characterized by exocrine pancreatic insuffi-ciency, bone marrow dysfunction, and metaphyseal chondrodysplasia. Recent studies show that mutations of SBDS, a gene of unknown function, are present in the majority of patients with SDS. In the present study, we show that most, but not all, patients classified based on rigorous clinical criteria as having SDS had compound heterozygous mutations of SBDS. Full-length SBDS protein was not detected in leukocytes of SDS patients with the most common SBDS mutations, consistent with a loss-of-function mechanism. In contrast, SBDS protein was expressed at normal levels in SDS patients without SBDS mutations. These data confirm the absence of SBDS mutations in this subgroup of patients and suggest that SDS is a genetically heterogeneous disorder. The presence (or absence) of SBDS mutations may define subgroups of patients with SDS who share distinct clinical features or natural history. (Blood. 2004;104: 3588-3590) Introduction Shwachman-Diamond Syndrome (SDS) is a rare multisystem disorder characterized by exocrine pancreatic insufficiency, bone marrow dysfunction, and metaphyseal chondrodyspla-sia. 1-5 SDS is the second most common cause of congenital exocrine pancreatic insufficiency, after cystic fibrosis. Bone marrow dysfunction is present in nearly all patients with SDS. 3-6 In the largest published series (88 patients), chronic or intermittent neutropenia was present in 97%. 5 Anemia and thrombocyto-penia were present in more than a third of patients. Patients with SDS have a marked propensity to develop myelodysplasia or acute myeloid leukemia. 6-8 SDS is inherited in an autosomal recessive fashion. 9 Recently , Boocock et al 10 reported that compound heterozygous mutations of the SBDS (Shwachman-Bodian-Diamond syndrome) gene on chromosome 7 were present in the majority of patients with SDS. Most of these mutations resulted from gene conversion with a neighboring pseudogene (SBDSP). Similar data were reported in a smaller series of patients of Japanese ancestry. 11 Most of the SBDS mutations are predicted to truncate a substantial portion of the SBDS protein, suggesting that they act in a loss-of-function manner. Herein, we show that most, but not all, patients classified prospectively based on clinical criteria as having probable SDS had SBDS gene mutations. Moreover, a strong correlation between SBDS genotype and expression of full-length SBDS protein was observed. Study design Human subjects There were 33 families who attended the Second International Conference on Shwachman-Diamond Syndrome in St Louis in 1999 and who were invited to participate in a study to elucidate the genetic basis of SDS. After obtaining informed consent, a thorough history, physical examination, review of medical records, and selected laboratory testing were performed. In addition, genomic DNA was extracted from peripheral blood leukocytes using standard protocols. The diagnosis of SDS was based on the presence of the followin...