The Genetics of Type 2 Diabetes:

The treatment of type 2 diabetes mellitus in youth : which therapies?

Type 2 diabetes mellitus in children and adolescents is becoming an increasingly important public health concern throughout the world. This epidemic is closely associated with the increased prevalence of obesity among youth of all ethnic backgrounds, as increased visceral adipose tissue produces adipokines that increase insulin resistance. Type 2 diabetes represents one arm of the metabolic syndrome, which includes abdominal obesity, disturbed glucose regulation and insulin resistance, dyslipidemia, and hypertension. The treatment of type 2 diabetes and the metabolic syndrome poses a challenge for pediatric endocrinologists. This review provides information regarding diagnosis of type 2 diabetes in children, as well as prevention strategies, such as lifestyle modification and pharmacologic options for weight loss, including metformin, orlistat, and sibutramine. Pharmacologic treatment options, their modes of action, and clinical indications for use are also reviewed. Treatment regimens for youth-onset type 2 diabetes that are discussed include metformin, sulfonylureas, glucosidase inhibitors, thiazolidinediones, glucagon-like peptide-1, and insulin.

Epidemiologic perspectives of risk for developing diabetes and diabetes complications

The incidence and prevalence of diabetes is increasing worldwide. National recommendations for screening and diagnosis of diabetes, hypertension, and dyslipidemia provide a basis for early detection, treatment, and intervention that may potentially decrease related complications, and personal and economic costs of the disease. Most important is that knowledge exists about who is at risk for diabetes by weight, family history of diabetes, ethnicity, and history of gestational diabetes that allows for the development and implementation of diabetes primary prevention programs. Multiple national health care providers, systems of care, and communities that can be used to guide such prevention, early screening, and disease detection and intervention programs aimed at decreasing the burden of diabetes.

Understanding the development and prevention of type 2 diabetes in youth (part 1)

The prevalence of being at risk of overweight, overweight, pre-diabetes, and type 2 diabetes is increasing in the United States in youth. Primary care providers must understand how the emerging epidemic of type 2 diabetes developed during the past several decades to accurately diagnose it in young patients. Primary, secondary, and tertiary prevention interventions are needed to address the emerging epidemic of type 2 diabetes in youth. Primary prevention involves delaying the development of type 2 diabetes by reducing the prevalence of overweight. Secondary prevention is aimed at preventing those with pre-diabetes from developing diabetes, and tertiary prevention is aimed at preventing the complications of type 2 diabetes.

Association between MspI polymorphism of the APO AI gene and Type 2 diabetes mellitus

AIMS

Genes of the Apo AI/CIII/AIV cluster on chromosome 11 have been related to plasma lipid patterns. The close relationship between carbohydrate metabolism and lipid metabolism warrants investigation of the association between this cluster and Type 2 diabetes mellitus. We therefore examined the possible association between polymorphisms of this cluster and Type 2 diabetes mellitus as part of a study of the prevalence of diabetes and the metabolic syndrome in southern Spain.

METHODS

A total of 1224 persons were selected randomly from the town of Pizarra in the province of Malaga, southern Spain. The sample errors for the prevalence of Type 2 diabetes mellitus and the three polymorphisms studied were all < or = 4%. All subjects underwent phenotyping after an oral glucose tolerance test (75 g) (WHO 1998 criteria) and the XmnI and MspI polymorphisms of Apo AI and the SstI polymorphism of Apo CIII were genotyped.

RESULTS

Those subjects with the mutated AA genotype of the MspI polymorphism (-75 G-->A) of Apo AI had a greater risk of impaired glucose tolerance [odds ratio (OR) = 1.95, CI = 1.02-3.8, P = 0.05], Type 2 diabetes mellitus, both known (OR = 7.38, CI = 1.3-39.7, P = 0.02) and unknown (OR = 3.7, CI = 1.4-9.9, P = 0.009). This risk was independent of age, sex, obesity, triglyceride level, HDL cholesterol and pattern of insulin resistance.

CONCLUSIONS

Pending confirmation in prospective studies, the AA genotype of the MspI polymorphism of the Apo AI gene, within the Apo A-I/C-III/A-IV cluster, seems to be a risk factor for Type 2 diabetes mellitus.

Genome-wide association studies for common diseases and complex traits

Genetic factors strongly affect susceptibility to common diseases and also influence disease-related quantitative traits. Identifying the relevant genes has been difficult, in part because each causal gene only makes a small contribution to overall heritability. Genetic association studies offer a potentially powerful approach for mapping causal genes with modest effects, but are limited because only a small number of genes can be studied at a time. Genome-wide association studies will soon become possible, and could open new frontiers in our understanding and treatment of disease. However, the execution and analysis of such studies will require great care.

Relationship of depression to diabetes types 1 and 2: epidemiology, biology, and treatment

This article reviews the rapidly accumulating literature on the relationship between mood disorders and diabetes mellitus. Recent studies have demonstrated that depression and its associated symptoms constitute a major risk factor in the development of type 2 diabetes and may accelerate the onset of diabetes complications. Since the mid-1980s, multiple longitudinal and cross-sectional studies have scrutinized the association of diabetes with depressive symptoms and major depression. Utilizing the search terms depressive disorders, psychiatry, diabetes, and pathophysiology in MEDLINE searches (1966-2003), this article reviews studies investigating pathophysiological alterations related to glucose intolerance and diabetes in depressed patients. The few randomized, controlled studies of treatment of depression in patients with diabetes are also described. Short-term treatment of depression in patients with diabetes improves their dysphoria and other signs and symptoms of depression. Future research will confirm whether response to psychotherapy and/or psychopharmacologic treatment improves glucose control, encourages compliance with diabetes treatment, and perhaps even increases longevity.

Pathogenesis of diabetes: our current understanding

Understanding the pathogenesis of any disease is of prime importance when considering treatment. Recent breakthroughs in the evaluation and management of diabetes and the availability of new therapeutic regimens make it imperative that the primary care physician be aware of these advances to improve patient care. This article discusses our current understanding of the pathogenesis of both type 1 and type 2 diabetes mellitus. A glossary of pertinent genetic terms is included.

The dysmetabolic syndrome

The first unifying definition for the metabolic syndrome was proposed by WHO in 1998. In accordance to this, patients with type 2 diabetes mellitus or impaired glucose tolerance have the syndrome if they fulfil two of the criteria: hypertension, dyslipidaemia, obesity/abdominal obesity and microalbuminuria. Persons with normal glucose tolerance (NGT) should also be insulin resistant. About 40% of persons with impaired glucose tolerance (IGT) and 70% of patients with type 2 diabetes have features of the syndrome. Importantly, presence of the dysmetabolic syndrome is associated with reduced survival, particularly because of increased cardiovascular mortality. The dysmetabolic syndrome most likely results from interplay between several genes and an affluent environment. Compatible with the thrifty gene theory, common variants in genes regulating lipolysis, thermogenesis and glucose uptake in skeletal muscle account for a large part of such thrifty genes. However, hitherto unknown genes may still be identified by random gene approaches.

Genomewide linkage analysis of stature in multiple populations reveals several regions with evidence of linkage to adult height

Genomewide linkage analysis has been extremely successful at identification of the genetic variation underlying single-gene disorders. However, linkage analysis has been less successful for common human diseases and other complex traits in which multiple genetic and environmental factors interact to influence disease risk. We hypothesized that a highly heritable complex trait, in which the contribution of environmental factors was relatively limited, might be more amenable to linkage analysis. We therefore chose to study stature (adult height), for which heritability is approximately 75%-90% (Phillips and Matheny 1990; Carmichael and McGue 1995; Preece 1996; Silventoinen et al. 2000). We reanalyzed genomewide scans from four populations for which genotype and height data were available, using a variance-components method implemented in GENEHUNTER 2.0 (Pratt et al. 2000). The populations consisted of 408 individuals in 58 families from the Botnia region of Finland, 753 individuals in 183 families from other parts of Finland, 746 individuals in 179 families from Southern Sweden, and 420 individuals in 63 families from the Saguenay-Lac-St.-Jean region of Quebec. Four regions showed evidence of linkage to stature: 6q24-25, multipoint LOD score 3.85 at marker D6S1007 in Botnia (genomewide P<.06), 7q31.3-36 (LOD 3.40 at marker D7S2195 in Sweden, P<.02), 12p11.2-q14 (LOD 3.35 at markers D12S10990-D12S398 in Finland, P<.05) and 13q32-33 (LOD 3.56 at markers D13S779-D13S797 in Finland, P<.05). In a companion article (Perola et al. 2001 [in this issue]), strong supporting evidence is obtained for linkage to the region on chromosome 7. These studies suggest that highly heritable complex traits such as stature may be genetically tractable and provide insight into the genetic architecture of complex traits.