Autosome-wide linkage analysis of hip structural phenotypes in the Old Order Amish

INTRODUCTION

Fracture risk is associated with bone mineral density (BMD) and with other indices of bone strength, including hip geometry. While the heritability and associated fracture risk of BMD are well described, less is known about genetic influences of bone geometry. We derived hip structural phenotypes using the Hip Structural Analysis program (HSA) and performed autosome-wide linkage analysis of hip geometric structural phenotypes.

MATERIALS AND METHODS

The Amish Family Osteoporosis Study was designed to identify genes affecting bone health. BMD was measured at the hip using dual X-ray absorptiometry (DXA) in 879 participants (mean age+/-SD=49.8+/-16.1 years, range 18-91 years) from large multigenerational families. From DXA scans, we computed structural measures of hip geometry at the femoral neck (NN) and shaft (S) by HSA, including cross-sectional area (CSA), endocortical or inner diameter (ID), outer diameter (OD) buckling ratio (BR) and section modulus (Z). Genotyping of 731 highly polymorphic microsatellite markers (average spacing of 5.4 cM) and autosome-wide multipoint linkage analysis was performed.

RESULTS

The heritability of HSA-derived hip phenotypes ranged from 40 to 84%. In the group as a whole, autosome-wide linkage analysis suggested evidence of linkage for QTLs related to NN_Z on chromosome 1p36 (LOD=2.36). In subgroup analysis, ten additional suggestive regions of linkage were found on chromosomes 1, 2, 5, 6, 11, 12, 14, 15 and 17, all with LOD>2.3 except for our linkage at 17q11.2-13 for men and women age 50 and under for NN_CSA, which had a lower LOD of 2.16, but confirmed a previous linkage report.

CONCLUSIONS

We found HSA-derived measures of hip structure to be highly heritable independent of BMD. No strong evidence of linkage was found for any phenotype. Confirmatory evidence of linkage was found on chromosome 17q11.2-12 for NN_CSA. Modest evidence was found for genes affecting hip structural phenotypes at ten other chromosomal locations.

Relationship between vascular calcification and bone mineral density in the Old-order Amish

Vascular calcification and osteoporosis are common age-related processes that are influenced by both genetic and nongenetic factors. Whether common genes underlie these processes is not known. We measured coronary artery calcification (CAC), aortic calcification (AC), and bone mineral density (BMD) in 682 men and women from large Old-Order Amish families. We assessed the heritabilities of these traits and then evaluated, using variance decomposition procedures, whether variation in the traits was influenced by a common set of genes (i.e., pleiotropy). Significant heritabilities were detected for BMD of the femoral neck and spine (0.65, 0.63) and CAC and AC (0.43, 0.42). Mean BMD did not differ significantly across quartiles of either CAC or AC in either sex. In neither the total group nor any single subgroup (men, women, postmenopausal women) did any of the genetic or environmental correlations between BMD and vascular calcification achieve statistical significance. However, subjects with a history of cardiovascular disease (CVD) events had significantly lower BMD at the femoral neck compared to subjects who reported no prior history of CVD (age-, sex-, body mass index-, and family structure-adjusted P = 0.003). We detected no evidence for shared genes affecting the joint distribution of bone and vascular calcification. However, our results do reveal a lower BMD in subjects with a prior history of CVD in the Old-Order Amish.

Mutation screening of the TNFRSF11A gene encoding receptor activator of NF kappa B (RANK) in familial and sporadic Paget's disease of bone and osteosarcoma

Paget's disease of bone (PDB) is a common disorder characterized by focal areas of increased and disorganized osteoclastic bone resorption, leading to bone pain, deformity, pathological fracture, and an increased risk of osteosarcoma. Genetic factors play an important role in the pathogenesis of Paget's disease. In some families, the disease has been found to be linked to a susceptibility locus on chromosome 18q21-22, which also contains the gene responsible for familial expansile osteolysis (FEO)--a rare bone dysplasia with many similarities to Paget's disease. Insertion mutations of the TNFRSF11A gene encoding Receptor Activator of NF kappa B (RANK) have recently been found to be responsible for FEO and rare cases of early onset familial Paget's disease. Loss of heterozygosity (LOH) affecting the PDB/FEO critical region has also been described in osteosarcomas suggesting that TNFRSF11A might also be involved in the development of osteosarcoma. In order to investigate the possible role of TNFRSF11A in the pathogenesis of Paget's disease and osteosarcoma, we conducted mutation screening of the TNFRSF11A gene in patients with familial and sporadic Paget's disease as well as DNA extracted from Pagetic bone lesions, an osteosarcoma arising in Pagetic bone and six osteosarcoma cell lines. No specific abnormalities of the TNFRSF11A gene were identified in a Pagetic osteosarcoma, the osteosarcoma cell lines, DNA extracted from Pagetic bone lesions, or DNA extracted from peripheral blood in patients with familial or sporadic Paget's disease including several individuals with early onset Paget's disease. These data indicate that TNFRSF11A mutations contribute neither to the vast majority of cases of sporadic or familial PDB, nor to the development of osteosarcoma.

Studies in a kindred with parathyroid carcinoma

We report a family with primary hyperparathyroidism in four patients in two generations with apparent autosomal dominant transmission. A fifth member was probably affected. Two cases had definite parathyroid carcinoma (PC), and two had parathyroid adenoma with atypical features that could represent an early stage of cancer. In each of our patients, one parathyroid gland was abnormal. Five other parathyroid glands (in two patients) were normal in histology and size. There was no evidence of neoplasia in other tissues. Constitutional karyotypes were normal in all four patients. We identified three chromosomal abnormalities (a reciprocal translocation between chromosomes 3 and 4, trisomy 7, and a pericentric inversion in chromosome 9) in cultured PC tissue from one patient. These chromosomal changes are of unclear significance. Analyses on tumor DNA from one case of PC and one of atypical adenoma showed no evidence of ras gene mutations, PTH gene rearrangement, or allelic loss from chromosome 11q13 (locus of the gene for multiple endocrine neoplasia type 1). This family shows susceptibility to cancer without antecedent hyperplasia in all parathyroids. It could help identify a novel tumor susceptibility gene.

Biology of bone endothelial cells

Cultured endothelial cells are used as tools to study the involvement of endothelium in various physiological and pathological processes. Significant physiological differences exist among endothelial cells from different districts. Microvascular endothelium is an integral part of bone tissue. Bone endothelial cells have been cloned from fetal bovine sternum. They show differentiated characteristics and a novel response to parathyroid hormone. This 'in vitro' model will make possible the analysis of possible influences of the endothelium on bone formation and resorption. The possibility that bone endothelial cells actively participate in the bone remodelling process is proposed.

Cloned endothelial cells from fetal bovine bone

Primary cell cultures from fetal bovine sternum were developed in Coon's modified Ham's F-12 medium containing 10% Nu-Serum, 1% Ultroser-G, and 200 mg of galactose per liter. Clones were obtained by colony isolation; one clone, BBE-1, was selected for characterization. BBE-1 cells exhibited typical endothelial morphology by light and electron microscopy and immunofluorescence for factor VIII-related antigen throughout their life span of 8 months. The cells showed mitogenic responses to endothelial cell growth factor, basic fibroblast growth factor, insulin-like growth factor types I and II, platelet-derived growth factor, ascorbic acid, and progesterone. Parathyroid hormone stimulated intracellular accumulation of cAMP in BBE-1 cells but not in endothelial cells from two other tissues. These clonal cells provide a useful system for studies on bone vasculature, including its interactions with other bone cells.

Anti-endothelial cell antibodies: detection and characterization in sera from patients with autoimmune hypoparathyroidism

In a previous report, we described antibodies in autoimmune hypoparathyroidism (AHP) that are cytotoxic for cultured bovine parathyroid cells. In the present study, we show that sera from six AHP patients, but not from 26 patients with other autoimmune diseases or from 7 healthy subjects, react with bovine endothelial cells in culture (by flow cytometry and fluorescence microscopy) and in tissue sections (by immunohistology). We found uniformly that the immunoglobulin class reacting is IgM. Adsorption experiments showed that the antigenic determinants reacting with AHP sera were similar on bovine cultured endothelial cell membranes and in tissue sections of bovine parathyroid glands. The AHP sera also reacted with endothelial cells cultured from bovine adrenal medulla and pulmonary artery. Immunoblot analysis showed antibody binding to two major bands of 200 and 130 kDa solubilized from the membrane fraction of bovine parathyroid endothelial cells. Only one AHP serum consistently recognized endothelium-related structures on frozen sections of three different human parathyroid adenomas; two other sera reacted with one adenoma each; and three did not react with human adenomas. This indicates that human material is less suitable than bovine in detecting endothelium-related immune phenomena in AHP sera. The anti-endothelium IgM antibodies appear to be disease-specific but are not organ- or species-specific. The identification of endothelial cells as the target for antibodies in AHP raises the possibility that the endothelium subserves an important local function for endocrine epithelium.

Marfan syndrome: exclusion of genetic linkage to three major collagen genes

The Marfan syndrome is an autosomal dominant connective tissue disorder with pleiotropic manifestations affecting skeletal, ocular and cardiovascular systems. Because the fibrillar collagens are major structural components of connective tissue, the hypothesis has long been set forth that the Marfan syndrome is a disorder of fibrillar collagen. We have investigated this hypothesis by performing linkage studies in 12 multiplex families with the Marfan syndrome, using restriction fragment length polymorphisms (RFLP's) associated with 3 genes encoding chains of fibrillar collagens. The data exclude linkage to all 3 candidate genes in 2 families and at least 1 of the candidates is excluded in 6 additional families. Each candidate was excluded in at least 3 families. In no case was strong evidence in favor of linkage of the Marfan syndrome to any of the 3 genes observed. These data speak against the hypothesis that mutations in one or more of these 3 fibrillar collagens cause the classic Marfan syndrome.

The Stickler syndrome: evidence for close linkage to the structural gene for type II collagen

The Stickler syndrome is an autosomal dominant hereditary disorder of connective tissue with pleiotropic features including premature osteoarthropathy, mild spondyloepiphyseal dysplasia, vitreoretinal degeneration, and the Pierre-Robin sequence. Genetic linkage studies in two families with the Stickler syndrome have been performed using restriction fragment length polymorphisms associated with the structural gene for type II collagen, COL2A1. No recombinants between the Stickler phenotype and COL2A1 were observed. The total LOD score for linkage of the Stickler syndrome and COL2A1 at a recombination fraction (theta) of zero is 3.59. These findings suggest that, at least in some families, the mutation causing Stickler syndrome affects the structural locus for type II collagen.

Pulmonary function in the Marfan syndrome

To explore the causes of reported abnormalities in pulmonary function in persons with the Marfan syndrome, we analyzed retrospective anthropometric and pulmonary function tests in 79 patients. For ten subjects, there were matched, related control subjects who did not have a connective tissue disorder. Patients had lower values of FVC and TLC than the values expected for their standing heights (83 and 91 percent). However, when sitting height was used to calculate expected spirometric values, patients free of severe deformity of the thoracic cage did not have significant spirometric abnormalities (FVC 105 percent, FEV1 92 percent). However, patients with moderate-to-severe pectus excavatum or scoliosis (common features of the Marfan syndrome) had marked reductions in total lung capacity as well as in FVC and FEV1, suggesting a restrictive ventilatory defect. The abnormalities of pulmonary function often found in clinical laboratories can be explained in most cases by inappropriate use of standing height to calculate expected values, by thoracic cage deformity, or by both. We have found no evidence from standard tests of pulmonary function for a connective tissue defect of lung parenchyma that is of clinical importance in Marfan patients who lack chest wall deformity.

Amyloid infiltration of the diaphragm as a cause of respiratory failure

Respiratory involvement with amyloidosis typically involves the tracheobronchial tree or lung parenchyma. We describe a patient with systemic amyloidosis who was respirator-dependent because of extensive amyloid infiltration of the diaphragm, with no evidence of other pulmonary amyloidosis. Diaphragmatic myopathy from amyloid should be considered in respiratory failure in amyloidosis.

"Blue-body" epithelial cell inclusions in conjunctivitis

In 10.4% of conjunctival scrapings received from 1731 patients with conjunctivitis during the years 1970 through 1980, basophilic cytoplasmic inclusions of unknown etiology were found in the epithelial cells when Giemsa stained. These "blue-bodies" differed in morphology from bacteria, chlamydia, and other frequent cytoplasmic inclusions. By electron microscopy, they consisted of a variety of dense bodies and phagolysosomal vacuoles containing complex lipids, indicating injury to the epithelial cells. The presence of these inclusions had a statistically significant association with the use of topical medications, especially Neosporin. Administration of other antibiotics and medications was less frequently related. Patients with the most prolific "blue-body" inclusions usually showed a clinical picture of subacute to chronic conjunctivitis or blepharoconjunctivitis thought to represent hypersensitivity. Recognizing the nature of these easily seen inclusions is important to distinguish them from infectious organisms, and may also support the diagnosis of a drug-related reaction.