Shwachman-Diamond syndromes: clinical, genetic, and biochemical insights from the rare variants.

Shwachman-Diamond syndrome is a rare inherited bone marrow failure syndrome characterized by neutropenia, exocrine pancreatic insufficiency, and skeletal abnormalities. In 10-30% of cases, transformation to a myeloid neoplasm occurs. Approximately 90% of patients have biallelic pathogenic variants in the SBDS gene located on human chromosome 7q11. Over the past several years, pathogenic variants in three other genes have been identified to cause similar phenotypes; these are DNAJC21, EFL1, and SRP54. Clinical manifestations involve multiple organ systems and those classically associated with the Shwachman-Diamond syndrome (bone, blood, and pancreas). Neurocognitive, dermatologic, and retinal changes may also be found. There are specific gene-phenotype differences. To date, SBDS, DNAJC21, and SRP54 variants have been associated with myeloid neoplasia. Common to SBDS, EFL1, DNAJC21, and SRP54 is their involvement in ribosome biogenesis or early protein synthesis. These four genes constitute a common biochemical pathway conserved from yeast to humans that involve early stages of protein synthesis and demonstrate the importance of this synthetic pathway in myelopoiesis.

Enzyme replacement in advanced pancreatic cancer: patient perceptions.

PURPOSE: Advanced pancreatic cancer has a universally poor survival rate. Patients frequently develop malabsorption that requires pancreatic enzyme replacement therapy (PERT). This study explores the experience of patient engagement with PERT and how the medication is taken and tolerated. METHODS: Participants with advanced pancreatic cancer requiring PERT were interviewed after referral to a specialist palliative care team. An inductive analysis was used to code the data. Theoretical sufficiency was reached after 12 participants. RESULTS: Four themes emerged from the interviews-patient context, health literacy, relationship to food and experience of taking the pancreatic enzymes. Respondents brought their own life experiences into the clinical encounter when told of the diagnosis. Patients had high levels of understanding and engagement with the diagnosis and treatment, understood the benefits of PERT in digestion and tolerated the medication well. CONCLUSIONS: Patients with metastatic pancreatic cancer understand the life-limiting nature of their illness. They want to participate in their healthcare decisions and are capable of complex medication titration when given good explanations and they experience benefits. PERT should be offered to these patients by a team of knowledgeable health professionals with good communication skills that can continue to support and review their needs.

The pancreatic exocrine function in patients with pancreatic endocrine insufficiency: the evaluation with cine-dynamic magnetic resonance cholangiopancreatography using a spatially selective inversion-recovery pulse and T1 mapping.

PURPOSE: To evaluate the association of the pancreatic exocrine function estimated by cine-dynamic magnetic resonance cholangiopancreatography (MRCP) using a spatially selective inversion-recovery (IR) pulse with the pancreatic endocrine function estimated by the T1 relaxation time of the pancreatic parenchyma and HbA1c values. MATERIALS AND METHODS: Forty-three patients with suspected hepatobiliary or pancreatic diseases were included. Patients were classified into three groups: HbA1c < 5.7% (normal group), 5.7% ≤ HbA1c < 6.5% (prediabetes group), and HbA1c ≥ 6.5% (diabetes group). The frequency of the secretory flow of the pancreatic juice was observed within the area of the IR pulse, and the moving distance (mean secretion grade) of the pancreatic juice inflow within the area of the IR pulse on cine-dynamic MRCP, and the T1 relaxation time of the pancreatic parenchyma on the T1 map images were assessed. The MR imaging measurements were compared using Spearman's rank correlation coefficient analysis and the Kruskal-Wallis and Mann-Whitney U tests. RESULTS: Both the mean secretion grade and frequency of the pancreatic secretory inflow had a significant negative correlation with the T1 relaxation time of the pancreatic parenchyma (r = - 0.335, p = 0.028 and r = - 0.305, p = 0.047, respectively) and HbA1c values (r = - 0.308, p = 0.044 and r = - 0.313, p = 0.041, respectively). Both the mean secretion grade and frequency of the pancreatic secretory inflow in the elevated HbA1c (prediabetes and diabetes) group were significantly lower than those in the normal group (p = 0.030 and p = 0.029, respectively). CONCLUSION: The pancreatic exocrine function estimated by cine-dynamic MRCP was significantly lower in patients with prediabetes and diabetes than in controls. Cine-dynamic MRCP with a spatially selective IR pulse may be useful for the early diagnosis of pancreatic exocrine insufficiency in patients with pancreatic endocrine insufficiency.

Exocrine pancreatic insufficiency related fat malabsorption and its association with autonomic neuropathy in Asian Indians with type 2 diabetes mellitus.

BACKGROUND AND AIMS: We aimed to estimate the prevalence of exocrine pancreatic insufficiency (EPI) related fat malabsorption & to correlate it with measures of autonomic neuropathy in patients with T2DM from India. METHODS: Patients with T2DM (cases; n = 118) and normo-glycaemic individuals (controls; n = 82) underwent anthropometry and biochemical evaluation at baseline. The 72-hours fecal fat excretion was estimated by the Van de Kamer's titration method. Autonomic neuropathy was evaluated using an automated analyzer. RESULTS: The prevalence of EPI related fat malabsorption in cases was 45% (n = 53; 72 hours mean fecal fat level = 22.7 ± 5.6 g/day). Dysfunctions in the parasympathetic nervous system (PNS; 86.7%; p < 0.05), sympathetic nervous system (SNS; 92.4%; p < 0.05), and both; PNS + SNS (83.1%; p < 0.05) were significant. Amongst measures of PNS dysfunction, there was a significantly higher percentage of abnormal expiration: inspiration ratio (45.3%) and the 30:15 ratio (84.9%) (p < 0.05) in patients with T2DM and EPI related fat malabsorption. CONCLUSION: In this cross-sectional cohort of Asian Indian patients with T2DM (n = 118), EPI related fat malabsorption correlates significantly with autonomic dysfunction in patients with T2DM. However, these preliminary data need to confirmed in trials with more robust design.

Pancreatic exocrine insufficiency occurs in most patients following pancreaticoduodenectomy.

BACKGROUND: Pancreatic exocrine insufficiency (PEI) is a well-defined complication of malignant diseases and pancreatic resection; however, study results of PEI are less consistent. Assessment of PEI by estimation of fecal elastase (FE)-1 in stool by enzyme-linked immunosorbent essay (ELISA) is a relatively inexpensive, noninvasive, and simple test. This study assessed exocrine function of pancreas following pancreaticoduodenectomy (PD) by estimating FE-1. METHODS: This prospective hospital-based study involved 30 patients who had undergone PD for malignancy. All 30 patients had an uneventful postoperative period under the unit's enhanced recovery after surgery (ERAS) protocol with no Grade B, C postoperative pancreatic fistula/postpancreatectomy hemorrhage as per the International Study Group of Pancreatic Surgery (ISGPS) definitions. Stool samples were collected postoperatively 3 months after surgery from all patients irrespective of clinical symptoms. The analysis was based on a solid phase ELISA used for the quantitative determination of human elastase 1 in feces. Fecal elastase was considered normal if >200 µg/gm stool, moderately reduced if 100-200 µg/gm stool, and severely reduced if <100 µg/gm stool. RESULTS: Among 30 patients included, fecal elastase levels were moderately reduced in 10 (33.33%) and severely reduced in 20 (66.67%) patients (P <0.0001). Mean (± standard deviation) of fecal elastase was 87.12 ± 38.76 with median of 74.6 µg/gm stool. There was no significant difference in the fecal elastase levels between men and women (P = 0.057), age (P = 0.48), pancreatic duct diameter (P = 0.609), pancreatic texture (P = 0.286), and presence or absence of clinical symptoms (P = 0.181). CONCLUSIONS: PD was frequently associated with PEI. Unfortunately PEI is an under recognized and under treated long-term sequel of PD. Fecal elastase 1 should be performed routinely in both symptomatic and asymptomatic patients. Pancreatic enzyme replacement therapy should be considered in every patient after PD.

Dietary Protein and Amino Acid Deficiency Inhibit Pancreatic Digestive Enzyme mRNA Translation by Multiple Mechanisms.

BACKGROUND & AIMS: Chronic amino acid (AA) deficiency, as in kwashiorkor, reduces the size of the pancreas through an effect on mammalian target of rapamycin complex 1 (mTORC1). Because of the physiological importance of AAs and their role as a substrate, a stimulant of mTORC1, and protein synthesis, we studied the effect of acute protein and AA deficiency on the response to feeding. METHODS: ICR/CD-1 mice were fasted overnight and refed for 2 hours with 4 different isocaloric diets: control (20% Prot); Protein-free (0% Prot); control (AA-based diet), and a leucine-free (No Leu). Protein synthesis, polysomal profiling, and the activation of several protein translation factors were analyzed in pancreas samples. RESULTS: All diets stimulated the Protein Kinase-B (Akt)/mTORC1 pathway, increasing the phosphorylation of the kinase Akt, the ribosomal protein S6 (S6) and the formation of the eukaryotic initiation factor 4F (eIF4F) complex. Total protein synthesis and polysome formation were inhibited in the 0% Prot and No Leu groups to a similar extent, compared with the 20% Prot group. The 0% Prot diet partially reduced the Akt/mTORC1 pathway and the activity of the guanine nucleotide exchange factor eIF2B, without affecting eIF2α phosphorylation. The No Leu diet increased the phosphorylation of eIF2α and general control nonderepressible 2, and also inhibited eIF2B activity, without affecting mTORC1. Essential and nonessential AA levels in plasma and pancreas indicated a complex regulation of their cellular transport mechanisms and their specific effect on the synthesis of digestive enzymes. CONCLUSIONS: These studies show that dietary AAs are important regulators of postprandial digestive enzyme synthesis, and their deficiency could induce pancreatic insufficiency and malnutrition.

Low serum trypsinogen levels in chronic pancreatitis: Correlation with parenchymal loss, exocrine pancreatic insufficiency, and diabetes but not CT-based cambridge severity scores for fibrosis.

BACKGROUND: Chronic pancreatitis (CP) is a complex inflammatory disorder of the pancreas affecting acinar cells, duct cells, islet cells and inflammatory cells including fibrosis-producing stellate cells. Serum trypsinogen is a biomarkers of acinar cell function. AIM: To define the degree of correlation between low trypsinogen levels as a marker of acinar cell function and variable features of CP. METHODS: Serum samples from previously ascertained and well phenotyped case and control subjects from the North American Pancreatitis Study II (NAPS2) were used to measure serum trypsinogen levels in a commercial laboratory. Control samples were used to define normal ranges and compared with levels in CP patients with defined features. RESULTS: A final cohort of 279 CP patients and 262 controls from the NAPS2 studies were evaluated. In controls trypsinogen had a mean of 34.96 ng/ml and SD = 11.99. Cut-off values for low trypsinogen ranged from <20 to 10 ng/ml and very low trypsinogen at <10 ng/ml. Compared to controls, CP was associated with very low trypsinogen levels (p < 0.0001). Within CP, very low trypsinogen levels correlated with parenchymal loss (pancreatic surgery [p < 0.05]; atrophy with calcifications, [p < 0.001]), EPI (p < 0.01, trend p < 0.001) and diabetes (trend p < 0.01) but not CT-based criteria for fibrosis (pancreatic duct dilation, irregularity, strictures). CONCLUSIONS: Very low serum trypsinogen levels correlate with measures of acinar cell loss including surgical resection, atrophic-calcific CP, diabetes and functional symptoms EPI but not duct morphology criteria. Serum trypsinogen levels correlate with decreased acinar cell function and therefore have biomarker utility clinical management.

Liver and pancreas: 'Castor and Pollux' regarding the relationship between hepatic steatosis and pancreas exocrine insufficiency.

BACKGROUND: Pancreatic exocrine insufficiency (PEI) is found in 30-50% of diabetes mellitus (DM). Insulin resistance is triggering factor in both DM and nonalcoholic fatty liver disease (NAFLD). Therefore, we aimed to investigate frequency of PEI in NAFLD, and relationship of fecal pancreatic elastase (PE) levels with liver histology and pancreatic fat. METHODS: Ninety-seven biopsy proven NAFLD patients and 50 controls were enrolled. Pancreas exocrine functions were measured by PE. Magnetic resonance imaging-estimated proton density fat fraction (MRI-PDFF) was used to quantify fat. RESULTS: NAFLD patients had significantly lower PE levels than controls (297 [204-517] vs. 500 [298-678] µg/g, p < 0.01). PEI (PE < 200 µg/g) ratio of NAFLD patients (22.7%, n = 22) was higher than PEI ratio of controls (6%, n = 3) (p = 0.011). Among diabetic (n = 35) NAFLD patients, 9 (25.7%) exhibited PEI, compared to 13 (21%) of non-diabetics. There was no significant difference in patients with and without DM in terms of PEI (p = 0.592). Among NASH (n = 68) patients 16 (23.5%) exhibited PEI, compared to (20.7%) of non-NASH (p = 0.76). Multiple analysis revealed NAFLD as a predictor of PEI independent of age, sex and DM (OR = 4.892, p = 0,021). Mean pancreas MRI-PDFF was significantly higher in diabetics (13.7% ± 3.6% vs. 8.7% ± 5.1%, p = 0.001). There was no significant pancreas MRI-PDFF difference between NASH and non-NASH (P = 0.95). Mean pancreas MRI-PDFF was significantly higher in patients with PEI (13.7% ± 3.4% vs. 8.9% ± 5.2%, P < 0.01). CONCLUSION: This is the first study demonstrating the high frequency of PEI in NAFLD independent of DM. Moreover, increasing pancreatic steatosis appears to be associated with higher frequency of PEI in NAFLD.

Impact of Endocrine and Exocrine Insufficiency on Quality of Life After Total Pancreatectomy.

BACKGROUND: Total pancreatectomy (TP) is rarely performed due to concerns for endocrine and exocrine insufficiency and decreased quality of life (QoL). Renewed interest is seen in recent years, but large cohort studies remain scarce. This study was designed to evaluate endocrine and exocrine insufficiency after TP and its impact on QoL. METHODS: Adult patients (age ≥ 18 years) who underwent TP between 2008 and 2017 at Karolinska University Hospital with at least 6 months follow-up were included. Endocrine and exocrine insufficiency and QoL were assessed using validated questionnaires (EORTC QLQ-C30, QLQ-PAN26, PAID20, and DTSQs). Both pre- and postoperative questionnaires were available in a subgroup. RESULTS: Of 145 TP, 60 patients were eligible of whom 53 (88.3%) with a median of 21 months (interquartile range [IQR] 13-54) follow-up were included. Symptomatic hypoglycemia occurred in 90.6% (48/53) of patients, and 25% (12/48) experienced ≥ 1 episodes of loss of consciousness. The PAID20 revealed emotional burnout in seven patients (13.2%), whereas a high satisfaction score of diabetes treatment (median 28, IQR 24-32) was measured according to the DTSQs. Overall, 27 patients (50.9%) reported to have steatorrhea during a median of 2 days (IQR 0-4) in the past week. Overall QoL was reduced compared with a general population (66.7% vs. 76.4%; Δ9.7%) but did not differ with preoperative outcomes (n = 39, 66.7%; IQR 41.7-83.3 vs. 66.7%, IQR 50.0-83.3; P = 0.553) according to the EORTC QLQ-C30. CONCLUSIONS: Although the impact of endocrine and exocrine insufficiency on QoL after TP seems acceptable, the management of both insufficiencies should be further improved.

Delivery of pancreatic digestive enzymes into the gastrointestinal tract by pancreatic exocrine tissue transplant.

Exocrine pancreatic insufficiency, caused by disease-induced loss of pancreatic exocrine cells, may be treated through regenerative stem cell technologies that facilitate the production of pancreatic exocrine cells from induced pluripotent stem cells (iPSCs). However, delivering the digestive enzymes produced in the transplanted cells to the gastrointestinal tract remains a challenge. To generate an allogenic transplantation rat model, minced pancreas was transplanted into the gastric submucosal space with ablation of muscularis mucosa. In the allogenic transplantation, transplanted pancreatic cells were engrafted. Elevated amylase was detected in gastric juice, while transplanted cells disappeared through auto-digestion when the muscularis mucosa was not eliminated. Human iPSCs were differentiated into pancreatic exocrine cells by stage-specific treatment with growth factors and chemical compounds, and the differentiated pancreatic cells were implanted into the gastric submucosal space of nude rats. The transplanted cells were engrafted, and amylase was detected in the gastric juice in some cases. These findings suggest that transplantation of pancreatic exocrine cells into the gastric submucosal space with muscularis mucosa elimination will contribute to a regenerative approach for pancreatic exocrine insufficiency.

Zinc deficiency in patients with chronic pancreatitis.

BACKGROUND: Zinc is a key element in numerous proteins and plays an important role in essential cell functions such as defense against free radicals and DNA damage repair. Chronic pancreatitis (CP) is a chronic inflammation with progressive fibrosis of pancreas ultimately resulting in pancreatic exocrine insufficiency (PEI), which is associated with malnutrition. Studies analyzing zinc levels in patients with CP are sparse and lead to conflicting results. AIM: To investigate serum zinc levels in patients with CP of various etiologies. METHODS: Between October 2015 and March 2018, patients with a diagnosis of CP were identified and recruited from the Pancreatic Outpatient Clinic at the Karolinska University Hospital in Stockholm, Sweden. Demographic, clinical and laboratory data were analyzed. Etiology of CP was determined according to the M-ANNHEIM classification system into the following etiological subcategories: alcohol consumption, nicotine consumption, hereditary factors, efferent pancreatic duct factors and immunological factors. Pancreatic exocrine function was defined as normal (fecal elastase 1 > 200 µg/g), mildly reduced (100-200 µg/g) and severely reduced (fecal elastase 1 < 100 µg/g). RESULTS: A total of 150 patients were included in the analysis. Zinc deficiency (< 11 µmol/L) was present in 39 (26.0%) of patients: 22 females and 17 males. In the group of patients with zinc deficiency, 76.7% of patients had an exocrine pancreatic insufficiency (FE-1 < 200 µg/g). Older age was significantly associated with low zinc levels. Following a univariate analysis, patients aged 60-69 and patients ≥ 70 years of age had a significantly higher prevalence of zinc deficiencies compared to patients < 40 years of age [OR: 3.8, 95%CI (1.08-13.4); P = 0.04]; [OR 6.26, 95%CI (1.94-20.2), P > 0.002]. Smoking and number of pack-years were additionally associated with low zinc levels. The risk of zinc deficiency in current smokers and smokers with ≥ 20 pack-years was approximately three times higher compared to those who had never smoked. Gender, body mass index, etiology of CP, presence of diabetes mellitus, levels of glycated hemoglobin (HbA1c), bone mineral density, alcohol intake and presence of PEI were not associated with low zinc levels. CONCLUSION: Zinc deficiency is common in patients with CP and is significantly associated with age ≥ 60, smoking and the number of pack-years, but not with PEI.

Peripheral blood immunophenotyping in a large cohort of patients with Shwachman-Diamond syndrome.

Shwachman-Diamond syndrome (SDS) is one of the more common inherited bone marrow failure syndromes, characterized by neutropenia, occasional thrombocytopenia, and anemia. Bone marrow evaluation reveals an increased number of monocytes and mature B cells along with decreased granulocytes. However, little is known about the subpopulations of peripheral blood cells, and few previous publications have been based on a small number of patients. Here, we report a comprehensive immunophenotypic analysis from a cohort of 37 SDS patients who display impairment mostly in the myeloid compartment with a deficiency also in the number of B cells and CD4/CD8 double-negative T cells.

Macropolycyte in Pediatrics.

Macropolycytes are tetraploid neutrophils produced during accelerated myelopoiesis. They have been reported in adults with pernicious anemia, sepsis, and after cytotoxic chemotherapy. Two pediatric cases are reported, one after granulocyte colony-stimulating factor treatment and the other following Kawasaki disease, respectively.

Diagnosis, Treatment, and Molecular Pathology of Shwachman-Diamond Syndrome.

Shwachman-Diamond syndrome (SDS) is an inherited bone marrow failure syndrome classically associated with exocrine pancreatic dysfunction and neutropenia, with a predisposition toward progressive marrow failure, risk of myelodysplastic syndrome, and leukemia. Most patients carry biallelic mutations in the Shwachman-Bodian-Diamond Syndrome gene, which is an integral component of ribosome maturation and biogenesis. This article reviews the diagnosis, clinical characteristics, and treatment modalities of SDS, and reports advances in the understanding of the molecular pathophysiology of SDS.

Altered exocrine function can drive adipose wasting in early pancreatic cancer.

Malignancy is accompanied by changes in the metabolism of both cells and the organism1,2. Pancreatic ductal adenocarcinoma (PDAC) is associated with wasting of peripheral tissues, a metabolic syndrome that lowers quality of life and has been proposed to decrease survival of patients with cancer3,4. Tissue wasting is a multifactorial disease and targeting specific circulating factors to reverse this syndrome has been mostly ineffective in the clinic5,6. Here we show that loss of both adipose and muscle tissue occurs early in the development of pancreatic cancer. Using mouse models of PDAC, we show that tumour growth in the pancreas but not in other sites leads to adipose tissue wasting, suggesting that tumour growth within the pancreatic environment contributes to this wasting phenotype. We find that decreased exocrine pancreatic function is a driver of adipose tissue loss and that replacement of pancreatic enzymes attenuates PDAC-associated wasting of peripheral tissues. Paradoxically, reversal of adipose tissue loss impairs survival in mice with PDAC. When analysing patients with PDAC, we find that depletion of adipose and skeletal muscle tissues at the time of diagnosis is common, but is not associated with worse survival. Taken together, these results provide an explanation for wasting of adipose tissue in early PDAC and suggest that early loss of peripheral tissue associated with pancreatic cancer may not impair survival.

Mutations in the SRP54 gene cause severe congenital neutropenia as well as Shwachman-Diamond-like syndrome.

Congenital neutropenias (CNs) are rare heterogeneous genetic disorders, with about 25% of patients without known genetic defects. Using whole-exome sequencing, we identified a heterozygous mutation in the SRP54 gene, encoding the signal recognition particle (SRP) 54 GTPase protein, in 3 sporadic cases and 1 autosomal dominant family. We subsequently sequenced the SRP54 gene in 66 probands from the French CN registry. In total, we identified 23 mutated cases (16 sporadic, 7 familial) with 7 distinct germ line SRP54 mutations including a recurrent in-frame deletion (Thr117del) in 14 cases. In nearly all patients, neutropenia was chronic and profound with promyelocytic maturation arrest, occurring within the first months of life, and required long-term granulocyte colony-stimulating factor therapy with a poor response. Neutropenia was sometimes associated with a severe neurodevelopmental delay (n = 5) and/or an exocrine pancreatic insufficiency requiring enzyme supplementation (n = 3). The SRP54 protein is a key component of the ribonucleoprotein complex that mediates the co-translational targeting of secretory and membrane proteins to the endoplasmic reticulum (ER). We showed that SRP54 was specifically upregulated during the in vitro granulocytic differentiation, and that SRP54 mutations or knockdown led to a drastically reduced proliferation of granulocytic cells associated with an enhanced P53-dependent apoptosis. Bone marrow examination of SRP54-mutated patients revealed a major dysgranulopoiesis and features of cellular ER stress and autophagy that were confirmed using SRP54-mutated primary cells and SRP54 knockdown cells. In conclusion, we characterized a pathological pathway, which represents the second most common cause of CN with maturation arrest in the French CN registry.

Mesenchymal stromal cells from Shwachman-Diamond syndrome patients fail to recreate a bone marrow niche in vivo and exhibit impaired angiogenesis.

Shwachman-Diamond syndrome (SDS) is a rare multi-organ recessive disease mainly characterised by pancreatic insufficiency, skeletal defects, short stature and bone marrow failure (BMF). As in many other BMF syndromes, SDS patients are predisposed to develop a number of haematopoietic malignancies, particularly myelodysplastic syndrome and acute myeloid leukaemia. However, the mechanism of cancer predisposition in SDS patients is only partially understood. In light of the emerging role of mesenchymal stromal cells (MSCs) in the regulation of bone marrow homeostasis, we assessed the ability of MSCs derived from SDS patients (SDS-MSCs) to recreate a functional bone marrow niche, taking advantage of a murine heterotopic MSC transplant model. We show that the ability of semi-cartilaginous pellets (SCPs) derived from SDS-MSCs to generate complete heterotopic ossicles in vivo is severely impaired in comparison with HD-MSC-derived SCPs. Specifically, after in vitro angiogenic stimuli, SDS-MSCs showed a defective ability to form correct networks, capillary tubes and vessels and displayed a marked decrease in VEGFA expression. Altogether, these findings unveil a novel mechanism of SDS-mediated haematopoietic dysfunction based on hampered ability of SDS-MSCs to support angiogenesis. Overall, MSCs could represent a new appealing therapeutic target to treat dysfunctional haematopoiesis in paediatric SDS patients.

Molecular basis of the human ribosomopathy Shwachman-Diamond syndrome.

Mutations that target the ubiquitous process of ribosome assembly paradoxically cause diverse tissue-specific disorders (ribosomopathies) that are often associated with an increased risk of cancer. Ribosomes are the essential macromolecular machines that read the genetic code in all cells in all kingdoms of life. Following pre-assembly in the nucleus, precursors of the large 60S and small 40S ribosomal subunits are exported to the cytoplasm where the final steps in maturation are completed. Here, I review the recent insights into the conserved mechanisms of ribosome assembly that have come from functional characterisation of the genes mutated in human ribosomopathies. In particular, recent advances in cryo-electron microscopy, coupled with genetic, biochemical and prior structural data, have revealed that the SBDS protein that is deficient in the inherited leukaemia predisposition disorder Shwachman-Diamond syndrome couples the final step in cytoplasmic 60S ribosomal subunit maturation to a quality control assessment of the structural and functional integrity of the nascent particle. Thus, study of this fascinating disorder is providing remarkable insights into how the large ribosomal subunit is functionally activated in the cytoplasm to enter the actively translating pool of ribosomes.

Ataluren-driven restoration of Shwachman-Bodian-Diamond syndrome protein function in Shwachman-Diamond syndrome bone marrow cells.

Shwachman-Diamond syndrome (SDS) is a rare inherited recessive disease mainly caused by mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene, which encodes for the homonymous protein SBDS, whose function still remains to be fully established. SDS affects several organs causing bone marrow failure, exocrine pancreatic insufficiency, skeletal malformations, and cognitive disorders. About 15% of SDS patients develop myelodysplastic syndrome (MDS) and are at higher risk of developing acute myeloid leukemia (AML). Deficiency in SBDS expression has been associated with increased apoptosis and lack of myeloid differentiation in bone marrow hematopoietic progenitors. Importantly, most SDS patients carry nonsense mutations in SBDS. Since ataluren is a well-characterized small molecule inhibitor that can suppress nonsense mutations, here, we have assessed the efficacy of this drug in restoring SBDS expression in hematopoietic cells obtained from a cohort of SDS patients. Remarkably, we show that ataluren treatment readily restores SBDS protein expression in different cell types, particularly bone marrow stem cells. Furthermore, ataluren promotes myeloid differentiation in hematopoietic progenitors, reduces apoptotic rate in primary PBMCs, and brings mammalian target of rapamycin phosphorylation levels back to normal in both lymphoblasts and bone marrow mesenchymal stromal cells (BM-MSCs). Since a specific therapy against SDS is currently lacking, these results provide the rationale for ataluren repurposing clinical trials.