Genetic variation in WNT16 and its association with bone mineral density, fractures and osteoporosis in children with bone fragility.

Several genome-wide association studies (GWAS), GWAS meta-analyses, and mouse studies have demonstrated that wingless-related integration site 16 (WNT16) gene is associated with bone mineral density (BMD), cortical bone thickness, bone strength and fracture risk. Practically no data exist regarding the significance of WNT16 in childhood-onset osteoporosis and related fractures. We hypothesized that pathogenic variants and genetic variations in WNT16 could explain skeletal fragility in affected children. We screened the WNT16 gene by Sanger sequencing in three pediatric cohorts: 35 with primary osteoporosis, 59 with multiple fractures, and in 95 healthy controls. Altogether, we identified 12 variants in WNT16. Of them one was a rare 5'UTR variant rs1386898215 in genome aggregate and medical trans-omic databases (GnomAD, TOPMED; minor allele frequency (MAF) 0.00 and 0.000008, respectively). One variant rs1554366753, overrepresented in children with osteoporosis (MAF = 0.06 vs healthy controls MAF = 0.01), was significantly associated with lower BMD. This variant was found associated with increased WNT16 gene expression at mRNA level in fibroblast cultures. None of the other identified variants were rare (MAF < 0.001) or deemed pathogenic by predictor programs. WNT16 may play a role in childhood osteoporosis but genetic WNT16 variation is not a common cause of skeletal fragility in childhood.

PLS3 sequencing in childhood-onset primary osteoporosis identifies two novel disease-causing variants.

Altogether 95 children with primary bone fragility were screened for variants in PLS3, the gene underlying X-linked osteoporosis. Two children with multiple peripheral and spinal fractures and low BMD had novel disease-causing PLS3 variants. Children with milder phenotypes had no pathogenic variants. PLS3 screening is indicated in childhood-onset primary osteoporosis. INTRODUCTION: The study aimed to determine the role of pathogenic PLS3 variants in children's bone fragility and to elucidate the associated phenotypic features. METHODS: Two cohorts of children with bone fragility were screened for variants in PLS3, the gene underlying X-linked osteoporosis. Cohort I comprised 31 patients with childhood-onset primary osteoporosis of unknown etiology. Cohort II comprised 64 children who had sustained multiple fractures but were otherwise healthy. Clinical and radiological data were reviewed. Peripheral blood DNA was Sanger sequenced for coding exons and flanking intronic regions of PLS3. RESULTS: In two patients of cohort I, where other common genetic causes had been excluded, we identified two novel disease-causing PLS3 variants. Patient 1 was a male with bilateral femoral fractures at 10 years, low BMD (Z-score -4.1; 18 years), and multiple vertebral compression fractures. He had a novel nonsense variant in PLS3. Patient 2 was a girl with multiple long bone and vertebral fractures and low BMD (Z-score -6.6 at 6 years). She had a de novo missense variant in PLS3; whole exome sequencing and array-CGH identified no other genetic causes. Iliac crest bone biopsies confirmed low-turnover osteoporosis in both patients. In cohort II, no pathogenic PLS3 variants were identified in any of the subjects. CONCLUSIONS: Two novel disease-causing variants in PLS3 were identified in a boy and a girl with multiple peripheral and spinal fractures and very low BMD while no pathogenic variants were identified in children with less severe skeletal fragility. PLS3 screening is warranted in male and female patients with childhood-onset primary osteoporosis.

Imatinib mesylate alleviates diarrhea in a mouse model of intestinal allergy.

BACKGROUND: When sensitized epicutaneously and challenged orally with ovalbumin, Balb/c mice develop allergen-induced diarrhea. As mast cells play important roles in diarrhea, we studied whether allergic diarrhea could be alleviated with imatinib mesylate. METHODS: Balb/c mice were sensitized and challenged with ovalbumin and treated orally with imatinib. Cytokine mRNA expressions were determined with quantitative RT-PCR and numbers of small intestinal mast cells determined by staining for chloroacetate esterase and mucosal mast cell protease-1. Immunofluorescence staining was used to assess the intestinal CCL1 expression. KEY RESULTS: Ovalbumin-sensitized and challenged Balb/c mice developed diarrhea, which was associated with increased number of mast cells and expression of interleukin (IL)-4 and -13, and chemokines CCL1 and CCL17 in the small intestine. Treatment with imatinib reduced the incidence of diarrhea, inhibited the development of mastocytosis and jejunal mRNA expression of IL-13, CCL1, CCL17 and CCL22. Mast cell-deficient W/W(-V) mice, and surprisingly, also their mast cell-competent control (+/+) littermates failed to develop diarrhea as a response to ovalbumin. This strain-dependent difference was associated with the inability of +/+ and W/W(-V) mice to increase the number of intestinal mast cells and expression of IL-4, IL-13, CCL1 and CCL17 after ovalbumin challenge. CONCLUSIONS & INFERENCES: Development of allergic diarrhea is associated with the ability of mice to develop intestinal mastocytosis. Imatinib inhibited the development of intestinal mastocytosis, reduced the incidence of diarrhea, and reduced the expression of IL-13, CCL1, and CCL17. Targeting intestinal mast cells could be a feasible approach to treat allergic diarrhea.

Calvarial doughnut lesions and osteoporosis: a new three-generation family and review.

Familial calvarial doughnut lesions (CDLs; OMIM 126550) is a rare autosomal dominant low bone density disorder characterized by distinctive X-ray translucencies of the skull, multiple fractures, elevated serum alkaline phosphatase, and dental caries. Only three families comprising 22 cases and 29 sporadic cases with the disorder have been reported. We describe a three-generation family consisting of three cases with clinical, radiological, biochemical, and histological findings consistent with this condition. All affected family members presented with childhood onset primary osteoporosis and typical CDLs or hyperostosis of the skull. In addition, the youngest family member was diagnosed with congenital glaucoma and her paternal grandmother with chronic congestive glaucoma. Glaucoma has not been previously described in this disorder. Adult patients also had recurrent cranial nerve palsies. No pathogenic mutations in the genes encoding low density lipoprotein receptor-related protein 5 (LRP5) or type I collagen (COL1A1 or COL1A2) were identified, suggesting that the disorder is caused by another dominant, yet unidentified gene. The literature is reviewed.

Mast cells associate with T-cells and neointimal microvessels in giant cell arteritis.

OBJECTIVE: Mast cells (MCs) are known to be involved in the neovascularization and regulation of T cell responses. However, the presence of MCs in giant cell arteritis (GCA) is unknown. This prompted us to study the presence and phenotype of MCs in GCA. METHODS: Human GCA specimens collected for diagnostic purposes were examined with immunohistochemistry. Double immunostainings of MC tryptase with cathepsin G, vascular endothelial cell growth factor (VEGF), CD3, and CD31/D34 were performed. RESULTS: Double immunostainings showed that activated tryptase-, cathepsin G- and VEGF-expressing MCs associate with CD3+ T cells and CD31/CD34+ neointimal neovessels in the GCA lesions. CONCLUSIONS: The results suggest that MCs may contribute to the pathogenesis of GCA putatively by regulating the functions of other inflammatory cells and resident vessel wall cells. Importantly, MCs promote neovascularization, which is considered as a prerequisite for the neointimal thickening in GCA.

Drug therapies to prevent coronary plaque rupture and erosion: present and future.

Patients at high risk for coronary heart disease usually have a number of atherosclerotic plaques in their coronary arteries. Some plaques grow inward and, once they have caused a critical degree of luminal stenosis, lead to chronic anginal symptoms. Other plaques grow outward and remain silent unless they disrupt and trigger an acute coronary event. Either type of plaque may become vulnerable to rupture or erosion once they have reached an advanced stage. Typically, a highly stenotic fibrotic plaque is prone to erosion, whereas an advanced lipid-rich thin-cap fibroatheroma is prone to rupture. Because of the multitude and complex nature of the coronary lesions and our inability to detect silent rupture-prone plaques, the best practical approach to prevent acute coronary events is to treat the vulnerable patient, i.e., to eliminate the risk factors of coronary disease. Despite such preventive measures, a sizable number of patients still experience acute coronary events due to plaque erosion or rupture. Thus, there is room for new avenues to pharmacologically stabilize vulnerable plaques. The development of new noninvasive tools to detect the progression and regression of individual non-stenotic rupture-prone plaques will allow testing of such novel pharmacotherapies. Because no specific plaque-targeted therapies are available at present, we give an overview of the current pharmacotherapy to treat the vulnerable patient and also discuss potential novel therapies to prevent acute coronary events.