The present invention relates generally to the field of human genetics. Specifically, the present invention relates to methods and materials used to isolate and detect human diabetes mellitus predisposing gene, specifically the angiotensinogen (AGT) gene, some mutant alleles of which cause susceptibility to insulin-dependent diabetes melitus (IDDM). More specifically, the invention relates to germline mutations in the AGT gene and their use in the diagnosis of predisposition to IDDM. The invention also relates to the prophylaxis and/or therapy of diabetes associated with a mutation in the AGT gene. The invention further relates to the screening of drugs for diabetes therapy. Finally, the invention relates to the screening of the AGT gene for mutations, which are useful for diagnosing the predisposition to diabetes.
The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting the practice, are incorporated herein by reference, and for convenience, are referenced by author and date in the following text and respectively grouped in the appended List of References.
Diabetes mellitus is among the most common of all metabolic disorders, affecting up to 11% of the population by age 70. Type I diabetes (insulin dependent diabetes mellitus or IDDM) represents about 5 to 10% of this group and is the result of a progressive autoimmune destruction of the pancreatic β-cells with subsequent insulin deficiency. IDDM is characterized by a partial or complete inability to produce insulin. Patients with IDDM would die without daily insulin injections to control their disease.
Few advancements in resolving the pathogenesis of diabetes were made until the mid-1970s when evidence began to accumulate to suggest that IDDM had an autoimmune etiopathogenesis. It is now generally accepted that IDDM results from the chronic autoimmune destruction of the insulin producing pancreatic β-cells. Lymphocytes and other inflammatory cells have been observed within the islets of Langerhans in newly diagnosed IDDM patients and have been found preferentially in regenerating islets composed of β-cells rather than those of other cell types. This active immunological process is associated with a variety of autoantibodies to β-cells cytoplasmic and membrane antigens, insulin, and insulin receptors. Although the general mechanism by which IDDM occurs is known, IDDM becomes clinically evident only after the vast majority of pancreatic β-cells have been irrevocably destroyed and the individual becomes dependent upon exogenous insulin.
In both humans and diabetes-prone non-obese diabetic (NOD) mice, genes mapping to the major histocompatibility complex have been associated with susceptibility to IDDM and shown to be very important in the disease process (Todd, 1990). Studies of NOD mice have mapped at least 12 other susceptibility genes to specific chromosomal locations (Prochazaka et al., 1987; Todd et al., 1991; De Gouyon et al., 1993; Morahan et al., 1994; Serreze et al., 1994; Comall et al., 1991; Garchon et al., 1991). In humans, markers near the insulin/insulin-like growth factor loci have also been associated with IDDM (Bell et al., 1984).
Epidemiological and molecular genetic studies indicate that only 40% of the genetic susceptibility is due to alleles of the MHC class II genes, suggesting additional non-MHC genes are involved (Todd et al., 1988; Buzzetti. et al., 1998). Genome-wide searches and analyses of specific genes have identified more at least 17 loci that contribute to the disease (Buzzetti et al., 1998; Todd, 1995; Concannon et al., 1998; Hashimoto et al., 1994; Davies et al., 1994; Mein et al., 1998; Verge et al., 1998). Significant evidence for linkage was reported for a ˜-7 cM region on chromosome 1q42-43 (Concannon et al., 1998). This region of chromosome 1 contains the angiotensinogen (AGT) gene.
Non-insulin dependent diabetes mellitus (NIDDM) is one of the most common inherited diseases in man with an estimated prevalence in Caucasian populations of 8-10% (Harris et al., 1987). It is estimated to affect more than 100 million people worldwide (King and Zimmer, 1988; Harris et al., 1992). Clinically, NIDDM is a heterogenous disorder characterized by chronic hyperglycemia leading to progressive micro- and macrovascular lesions in the cardiovascular, renal and visual systems as well as diabetic neuropathy. The causes of the fasting hyperglycemia and/or glucose intolerance associated with this form of diabetes are not well understood. Unfortunately, the disease is associated with early morbidity and mortality. Subtypes of the disease can be identified based at least to some degree on the time of onset of the symptoms. The principal type of NIDDM occurs at a later time of onset, typically at midlife. Early-onset NIDDM or maturity-onset diabetes of the young (MODY) shares many features with the more common form(s) of NIDDM but onset occurs in early life.
Although most forms of NIDDM do not exhibit simple Mendelian inheritance, the contribution of heredity is well recognized (Rotter et al., 1990). The genetic basis of a few rare monogenic syndromes of NIDDM have been elucidated, but together, these syndromes account for a very small minority of cases (Taylor et al., 1992; Froguel et al., 1993; Steiner et al., 1990; Kadowaki et al., 1994). It is likely that the common forms of NIDDM are complex and heterogenous, and result when a pool of mutant genes, each of which contributes modestly and in a subtle way, interact with each other and with environmental, aging and behavioral influences to lead to the expression of the disease. This pool of genes may vary between populations and among individuals within a population, despite the illusion of a clinically homogenous phenotype.
Certain loci have been linked to rare early-onset forms of Type II diabetes that is associated with chronic hyperglycemia and monogenic inheritance (i.e. maturity onset diabetes of the young (MODY) loci) (Bell et al., 1991; Froguel et al., 1992; Hattersley et al., 1992; Vaxillaire et al., 1995). The defects in the glucokinase (GCK) gene on human chromosome 7 have been found to be responsible for the relatively rare MODY2 phenotype. (Froguel et al., 1992).
The genes responsible for MODY1 and MODY3 have been identified to be transcription factors hepatocyte nuclear factor 4 (HNF4) and hepatocyte nuclear factor 1 HNF 1, repsectively. (Yamagata et al., 1996a; Yamagata et al. 1996b). The diabetes gene HNF4/MODY1 regulates expression of the AGT gene (Yanai et al., 1999). Mutations in HNF4/MODY1 have been demonstrated to cause predisposition to maturity onset diabetes of the young. (MODY) a genetically heterogenouse monogenic form of non-insulin-dependent diabetes mellitus (NIDDM) (Yamagata et al., 1996b; Lindner et al., 1997).
Another locus has been identified for a rare early-onset form with mitochondrial inheritance (Van den Ouwenland et al., 1992). In addition, Harris et al. (1996) identified a locus of NIDDM1 on chromosome 2 that appears to play a role in Mexican American diabetes. Further, Mahtani et al. (1996) report evidence of the existence of a gene on human chromosome 12, NIDDM2, that causes NIDDM associated with low insulin secretion. The paper suggests that NIDDM2 and MODY3 represent different alleles of the same gene with severe mutations causing MODY3 and milder mutations giving rise to later-onset NIDDM characterized by low insulin secretion.
In view of the heterogeneity of genes associated with IDDM or NIDDM, it is desired to identify additional genes associated with IDDM or NIDDM for diagnostic and therapeutic purposes.