Down syndrome (DS) is a major cause of mental retardation and congenital heart disease. Besides a characteristic set of facial and physical features, DS is associated with congenital anomalies of the gastrointestinal tract, an increased risk of leukemia, immune system defects, and an AMzelmer-like dementia. Moreover, DS is a model for the study of human aneuploldy. Although With the discovery that DS was caused by trisomy 21 (3, 4), and the subsequent proposal that chromosome 21 band q22 was "pathogenetic" for DS (5), the foundation was laid for elucidating the fundamental biochemical and morphogenetic pathways of abnormal development in this aneuploidy. There followed a series ofreports ofindividuals with "partial trisomy 21" (for review, see ref. 6) that appeared to indicate that regions might be defined that were likely to contain genes responsible for particular features of DS. These studies provide the basis for construction of a DS phenotypic map.By "phenotype" we mean a measurable parameter and include clinical, physical, cellular, and physiological components. By "phenotypic mapping" we mean the molecular definition of a physical region that is likely to contain the gene(s) whose overexpression is ultimately responsible in part for the phenotype. The current revolution in human molecular genetics and the development of a physical map of chromosome 21 now provide the possibility to understand the genetic basis for some of these defects and, therefore, to provide a necessary first step for their prevention, amelioration, and perhaps ultimately, their treatment.Phenotypic maps provide the basis for clinical prognosis for individuals with partial aneuploidy for chromosome 21, and when of high resolution, the basis for the identification of the genes responsible for the phenotypes. One approach to this combines the phenotypic information from individuals with "partial trisomy" such as those described above with a molecular definition of their duplicated chromosomal regions. Once the molecular markers for a region are defined, the genes within it may then be identified, characterized, and ultimately tested for their relationship to a given phenotype. This report describes the molecular and phenotypic definition of these individuals, provides a theoretical framework, and utilizes this to construct a molecular "map" of the phenotypes associated with DS.

The intestinal epithelium is continually exposed to a high intraluminal concentration of diverse bacteria and bacterial products (1, 2). Despite the density of commensal bacteria and their products, the intestinal mucosa maintains a controlled state of inflammation. By contrast, invasive or toxin-producing pathogenic bacteria elicit acute inflammation and secretion of pro-inflammatory cytokines by intestinal epithelial cells and lamina propria mononuclear cells (3, 4). Idiopathic inflammatory bowel disease in humans and animals is characterized by acute and chronic inflammation in the absence of a specific pathogen. Compelling evidence in genetically susceptible animal models of inflammatory bowel disease demonstrates that Th1 cytokines and commensal bacteria are required for the induction of chronic inflammation (5-9). The recent discovery of a genetic association in inflammatory bowel disease patients with a mutation in a gene involved in LPS 1 signaling, NOD2, supports the idea that innate immunity may be defective in patients with idiopathic inflammatory bowel disease (10, 11).We wished to understand the mechanism by which the normal intestinal epithelium guards against chronic activation in the presence of commensal flora. Commensal gut bacteria include both Gram-positive and Gram-negative organisms (2). The cell wall of Gram-negative bacteria contains LPS, a potent pro-inflammatory pathogen-associated molecular pattern responsible for the systemic manifestations of septic shock (12). The response to LPS is mediated by its interaction with tolllike receptor 4 (TLR4) in conjunction with secreted MD-2 and soluble or membrane-bound CD14 and transduced via the IL-1 receptor signaling complex to activate NF-B and pro-inflammatory cytokine secretion (13-16). We and others have previously described that intestinal epithelial cells are unresponsive to purified, protein-free LPS as measured by 18). To determine the reason for LPS unresponsiveness, we assayed for the presence of TLR4 and its co-receptor MD-2 and found that intestinal epithelial cells express low levels of TLR4 and MD-2 (17). Expression of both TLR4 and MD-2 restores the ability of intestinal epithelial cells to respond to LPS, suggesting that the intracellular signaling pathway leading to NF-B is intact in these cells. These in vitro model systems are consistent with findings in normal adult human colonic biopsies, small intestinal resections, and fetal intestinal epithelial cells, which have demonstrated low TLR4 expression by immunohistochemistry and 19). These studies did not examine the expression of the MD-2 co-receptor, which is required for LPS responsiveness, nor did they measure TLR4 function.Little is known about the regulation of TLR4 or MD-2 expression. Whereas normal intestinal epithelial cells express

As the pathogenesis of pituitary adenomas remains unclear, the tumor clonal composition of these common neoplasms was studied. Clonality was determined in female patients by analysis of restriction fragment length polymorphisms of the X-chromosome genes hypoxanthine phosphoribosyl transferase and phosphoglycerate kinase in conjunction with their respective methylation patterns. Peripheral lymphocyte DNA was screened from 62 female patients undergoing transsphenoidal surgery for pituitary adenoma. Eleven patients were heterozygous for the BglI site on PGK, 4 for the BamHI site on HPRT, and 1 patient for both sites. Of these 16 patients, 3 had acromegaly, 4 had Cushing's disease, 7 had hyperprolactinemia, and 2 were clinically nonfunctional. After surgery, morphological study, including immunohistochemistry and electron microscopy of the pathological specimens, allowed a direct comparison between clonality and tumor cell type. Control fresh normal pituitary tissue was found to be polyclonal. The following tumors were monoclonal: all 3 somatotroph adenomas, 4 of 4 lactotroph tumors, 3 of 4 corticotroph cell adenomas, a gonadotroph adenoma, and a nonsecretory adenoma. A mixed plurihormonal adenoma was polyclonal, as were 2 tumors consisting of adenomatous lactotrophs interspersed with nontumorous adenohypophyseal pituitary tissue and one corticotroph adenoma mixed with normal pituitary tissue. Functional pituitary adenomas derived from somatotrophs, corticotrophs, or lactotrophs and nonsecretory tumors are monoclonal in nature, suggesting that somatic cell mutations precede clonal expansion of these cells and play a major role in pituitary tumorigenesis.