Heritability and familiality of type 2 diabetes and related quantitative traits in the Botnia Study.

AIMS/HYPOTHESIS: To study the heritability and familiality of type 2 diabetes and related quantitative traits in families from the Botnia Study in Finland. METHODS: Heritability estimates for type 2 diabetes adjusted for sex, age and BMI are provided for different age groups of type 2 diabetes and for 34 clinical and metabolic traits in 5,810 individuals from 942 families using a variance component model (SOLAR). In addition, family means of these traits and their distribution across families are calculated. RESULTS: The strongest heritability for type 2 diabetes was seen in patients with age at onset 35-60 years (h (2) = 0.69). However, including patients with onset up to 75 years dropped the h (2) estimates to 0.31. Among quantitative traits, the highest h (2) estimates in all individuals and in non-diabetic individuals were seen for lean body mass (h (2) = 0.53-0.65), HDL-cholesterol (0.52-0.61) and suppression of NEFA during OGTT (0.63-0.76) followed by measures of insulin secretion (insulinogenic index [IG(30)] = 0.41-0.50) and insulin action (insulin sensitivity index [ISI] = 0.37-0.40). In contrast, physical activity showed rather low heritability (0.16-0.18), whereas smoking showed strong heritability (0.57-0.59). Family means of these traits differed two- to fivefold between families belonging to the lowest and highest quartile of the trait (p < 0.00001). CONCLUSIONS/INTERPRETATION: To detect stronger genetic effects in type 2 diabetes, it seems reasonable to restrict inclusion of patients to those with age at onset 35-60 years. Sequencing of families with extreme quantitative traits could be an important next step in the dissection of the genetics of type 2 diabetes.

Characterization of the MODY3 phenotype. Early-onset diabetes caused by an insulin secretion defect.

Maturity-onset diabetes of the young (MODY) type 3 is a dominantly inherited form of diabetes, which is often misdiagnosed as non-insulin-dependent diabetes mellitus (NIDDM) or insulin-dependent diabetes mellitus (IDDM). Phenotypic analysis of members from four large Finnish MODY3 kindreds (linked to chromosome 12q with a maximum lod score of 15) revealed a severe impairment in insulin secretion, which was present also in those normoglycemic family members who had inherited the MODY3 gene. In contrast to patients with NIDDM, MODY3 patients did not show any features of the insulin resistance syndrome. They could be discriminated from patients with IDDM by lack of glutamic acid decarboxylase antibodies (GAD-Ab). Taken together with our recent findings of linkage between this region on chromosome 12 and an insulin-deficient form of NIDDM (NIDDM2), the data suggest that mutations at the MODY3/NIDDM2 gene(s) result in a reduced insulin secretory response, that subsequently progresses to diabetes and underlines the importance of subphenotypic classification in studies of diabetes.

Chronic complications in patients with slowly progressing autoimmune type 1 diabetes (LADA).

OBJECTIVE: To study the prevalence of chronic diabetic complications in patients with the slowly progressing autoimmune form of type 1 diabetes, also referred to as latent autoimmune diabetes in adults (LADA). RESEARCH DESIGN AND METHODS: We evaluated factors associated with chronic diabetic complications in 59 patients with GAD antibodies (GADAs) and age at onset of diabetes >35 years and in 59 GADA-negative type 2 diabetic patients. The prevalence of chronic complications was further compared with the prevalence in 111 type 1 diabetic patients. RESULTS: The LADA patients had lower BMI (P = 0.04), waist-to-hip ratio (P = 0.02 for men and P = 0.03 for women), and fasting C-peptide concentrations (P<0.001) higher HDL2 concentrations (P = 0.04), and less hypertension (58 vs. 75%, P = 0.05) than the type 2 diabetic patients. These differences were even more marked in patients with short disease duration. The prevalence of retinopathy (51 vs. 56%), neuropathy (29 vs. 27%), and microalbuminuria (27 vs. 29%) did not differ between the groups. The type 1 diabetic patients had lower prevalence of neuropathy (13%, P = 0.02) and higher prevalence of retinopathy (76%, P = 0.002) compared with the other groups. Neither the prevalence of coronary heart disease (CHD) (56 vs. 58%) nor cardiovascular mortality (7.4 vs. 12.4%, P = 0.2) significantly differed between the LADA and type 2 diabetic patients. In a multiple logistic regression analysis, glycemic control was associated with CHD (P = 0.02) in the LADA group but not in the type 2 diabetic group. CONCLUSIONS: Glycemic control is a stronger risk factor for cardiovascular disease in LADA patients than in patients with type 2 diabetes. This could be related to the lower prevalence of the metabolic syndrome seen in the former.

Genetic testing for maturity onset diabetes of the young: uptake, attitudes and comparison with hereditary non-polyposis colorectal cancer.

AIMS/HYPOTHESIS: Mutations in hepatic nuclear factor 1alpha cause a monogenic form of diabetes, maturity onset diabetes of the young type 3 (MODY3). Our aim was (1) to assess the uptake of genetic testing for MODY3 and to determine factors affecting it, and (2) to compare attitudes to predictive genetic testing between families with MODY3 and a previously studied group at risk of hereditary non-polyposis colorectal cancer (HNPCC). METHODS: Adult members of two extended MODY3 pedigrees, either with diabetes or a 50% risk of having inherited the mutation (n=144, age 18-60 years), were invited to an educational counselling session followed by a possibility to obtain the gene test result. Data were collected through questionnaires before counselling and 1 month after the test disclosure. RESULTS: Eighty-nine out of 144 (62%) participated in counselling, and all but one wanted the test result disclosed. No significant sociodemographic differences were observed between the participants and non-participants. The counselling uptake was similar among diabetic and non-diabetic subjects. Uncertainty about the future and the risk for the children were the most common reasons to take the gene test. At follow-up, most subjects in both MODY3 (100%) and HNPCC (99%) families were satisfied with their decision to take the test and trusted the result. The majority of both diabetic and non-diabetic subjects considered that the MODY3 gene test should be offered either in childhood (50 and 37%) or as a teenager (30 and 37%). CONCLUSIONS: Genetic testing for MODY3 was well accepted among both diabetic and non-diabetic participants. The subjects found the gene test reliable and they were satisfied with their decision regarding the predictive test.

Chronic diabetic complications in patients with MODY3 diabetes.

MODY3 diabetes, which is caused by a mutation in the hepatocyte nuclear factor-1alpha gene (HNF-1alpha) on chromosome 12, represents a relatively common monogenic form of diabetes in Finland. Age at onset of the disease can vary from 10 to 60 years, but little is known about the natural course of the disease, particularly the development of diabetes-related chronic complications. The availability of genetic markers now allows description of the clinical course of the disease. In order to examine the prevalence of chronic diabetic complications in MODY3, we examined 57 carriers with HNF-1alpha mutations for the presence of micro- and macrovascular complications. Thirty-four percent of the MODY patients had mild and 13% had severe non-proliferative or proliferative retinopathy; this figure did not differ from the figures in insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM) patients matched for duration and glycaemic control but not for age. Neither did the prevalence of microalbuminuria differ between MODY3 and IDDM or NIDDM patients (19 vs 24 and 23%). Neuropathy was observed with the same frequency as previously reported in IDDM. Hypertension was less frequent in MODY3 and IDDM than in NIDDM (24.5 and 19 vs 53.7%; p < 0.001). Coronary heart disease was more common in MODY3 than in IDDM (16 vs 4.5%; p < 0.02) but less common than in the older NIDDM patients (33.3%; p < 0.02). In a multiple logistic regression analysis, poor glycaemic control was an independent risk factor for retinopathy (p = 0.03), microalbuminuria (p < 0.04) and neuropathy (p = 0.03). In conclusion, microangiopathic complications are observed with the same frequency in patients with MODY3 diabetes as in IDDM and NIDDM and are strongly related to poor glycaemic control.