GHR exon 3 polymorphism: association with type 2 diabetes mellitus and metabolic disorder

Growth hormone (GH) signaling via the growth hormone receptor (GHR) forms a major part of the GH-IGF-I axis, which is crucial for controlling metabolism and anabolism. Two common variants of the GHR differ by the presence (full length or GHR(fl)) or absence of exon 3 (exon 3 deleted or GHR(d3)), the function of which is unknown. However, differential response to GH treatment has been observed with carriers of the GHR(d3) variant conferring a greater growth rate. This study investigates these GHR variants in subjects with normal glucose tolerance (NGT) and impaired glucose tolerance (IGT), including Type 2 diabetes mellitus (T2DM). DNA was extracted from blood samples from subjects with NGT (n=158), IGT (n=116) and T2DM (n=194). The T2DM subjects in set 1 (n= 39) were newly diagnosed, whilst those in set 2 (n=155) had a mean duration of 7 years. Set 1 also included NGT and IGT subjects. Genotyping by standard PCR and gel electrophoresis were carried out. A significant difference was observed between T2DM and NGT (p<0.0001) with a significantly lower frequency of GHR(d3) in T2DM (3.6% compared to 17% in NGT). Both sets of T2DM subjects with at least one GHR(d3) allele had significantly higher BMI. In the larger subset of T2DM, GHR(d3) was associated with higher CRP levels as well as age adjusted IGF-I, with a trend of higher C-peptide secretion and impaired lipid levels, indicating a phenotype with metabolic disorder when compared to the GHR(fl/fl) T2DM subjects. In conclusion, homozygosity for the GHR(d3) allele appears to be preventive of T2DM. However, when other factors cause overt T2DM, the GHR(d3) allele confers a phenotype indicative of metabolic disorder. This study supports the hypothesis that the two GHR alleles by their inclusion or exclusion of exon 3 are functionally different.

Leu7Pro polymorphism in the neuropeptide Y (NPY) gene is associated with impaired glucose tolerance and type 2 diabetes in Swedish men

The neuropeptide Y (NPY) is a neuropeptide with a role in the regulation of satiety and energy balance of body weight, insulin release, cardiovascular and central endocrine systems. In order to evaluate whether the NPY gene variations contribute to development of type 2 diabetes (T2DM), we have performed a genetic association study for Leu7Pro (T1128 C) polymorphism of the NPY gene in impaired glucose tolerance (IGT) and T2DM. Genotyping experiments for this non-synonymous single nucleotide polymorphism (SNP) in 263 patients with T2DM, 309 subjects with IGT and 469 non-diabetic healthy individuals in Swedish Caucasians were performed by using Dynamic Allele Specific Hybridisation (DASH). We found that the frequencies of the "risk" allele C in the subjects with IGT and the patients with T2DM in Swedish men were 13 % (p = 0.002, OR = 3.70, 1.65 - 8.29 95 % CI) and 10 % (p = 0.007, OR = 4.80, 1.47 - 11.33 95 % CI) respectively, which were significantly higher than the C allele frequency in non-diabetic controls (6 %). Furthermore, we found that the carriers with TC and CC genotypes in the subjects with IGT in Swedish men had significantly higher fasting plasma glucose in comparison with the TT carriers (5.6 +/- 0.7 mmol/l vs. 5.2 +/- 0.7 mmol/l, p = 0.021). The present study thus provides the evidence that Leu7Pro polymorphism in the NPY gene is associated with IGT and T2DM in Swedish men, and indicates that the NPY gene variations contribute to development of T2DM. Questions of gender specificity may be explained by genetic backgrounds, sense of coherence for stress and other factors in environment.

A rapid increase in beta-cell function by multiple insulin injections in type 2 diabetic patients is not further enhanced by prolonging treatment

OBJECTIVE

Intensive insulin treatment in type 2 diabetes can improve beta-cell function. It is not known which duration of treatment achieves maximal improvement. We addressed this question in type 2 diabetic patients who displayed features of 'secondary failure'.

RESEARCH DESIGN AND METHOD

Ten patients were randomized to multiple insulin injection (MI) therapy for 9 weeks. Another 10 patients started with bedtime insulin (BTI) and continued their peroral medication. Following 9 weeks of treatment, patients on MI switched to BTI and glibenclamide.

RESULTS

Three days of MI led to a decrease in fasting proinsulin/insulin ratio, 0.43 +/- 0.20 vs. 0.29 +/- 0.11, P=0.01 and an increase in glucagon-stimulated C-peptide over baseline, 0.77 +/- 0.43 vs. 1.28 +/- 0.44 nmol L-1, P 0.02. Nine weeks of MI treatment successively decreased fasting and nonfasting blood glucose in parallel with increasing insulin dosage. Initial improvements in secretion parameters were upheld but not further enhanced, the 9 week proinsulin/insulin ratio being 99 +/- 23% and that of glucagon-stimulated C-peptide being 95 +/- 24% of the values obtained after 3 days of treatment. Eight weeks after termination of MI there persisted a total weight gain that tended to be larger than after continuous peroral medication with BTI.

CONCLUSION

Improvement of insulin secretion by intensive insulin treatment is rapidly gained with no further effect obtained after a longer treatment period. This finding, as well as undesirable effects of MI on body weight, argues against prolonged MI treatment as a prelude to other therapeutic regimens in type 2 diabetic patients.