Many adolescents with type 1 diabetes (T1DM) have suboptimal glycaemic control, increasing the risk of diabetic complications. This thesis explores some of the causes, consequences and therapeutic options for adolescents with T1DM and poor glycaemic control. Insulin resistance occurs in T1DM and normal puberty and contributes to poor glycaemic control. The effect of rosiglitazone, an insulin sensitizer, in addition to insulin on the glycaemic control of adolescents with T1DM was tested using a randomized, double blind placebo controlled trial. Treatment with rosiglitazone did not improve HbA1c, however there was a significant reduction in insulin dose and adiponectin, suggesting improved in insulin sensitivity. Insulin sensitivity by euglycaemic hyperinsulinaemic clamp varied widely between individuals and there was no consistent pattern with rosiglitazone. Potential markers of insulin resistance in T1DM were examined. Total and high molecular weight (HMW) adiponectin levels were lower in children and adolescents with T1DM than controls. HMW adiponectin was significantly associated with other markers of insulin resistance, such as insulin dose, body mass index standard deviation score (BMI-SDS), age, pubertal stage and duration of diabetes. There is increasing evidence that insulin resistance may play a role in T1DM complications. The natural history and risk factors for the development of microalbuminuria was described using a retrospective cohort study of 972 children and adolescents. Most cases of microalbuminuria were transient. Apart from baseline albumin excretion rate, HbA1c and age at diagnosis, other predictors of subsequently developing persistent microalbuminuria included several markers of insulin resistance (higher cholesterol, BMI-SDS, and insulin dose). In addition to insulin resistance, there are many other factors that contribute to glycaemic control. The role of the variability in carbohydrate intake was assessed using questionnaires and food diaries. Although carbohydrate consumption varied by approximately 45grams each day, it had no significant correlation with HbA1c. The impact of socioeconomic status, quality of life and health care delivery is discussed by comparing glycaemic control of children with T1DM in three diabetes centres. A model for the factors associated with poor glycaemic control in adolescents with T1DM is proposed, and the challenges of research and clinical practice in this population are discussed.

The metabolism of vitamin D commences with exposure of the skin to sunlight. The growing recognition of its role in insulin resistance, autoimmune disorders, infections, cancer, as well as the health of cells that influence physical and mental function have profound implications on how we define vitamin D requirements and why we should care whether they are met or not. Most of the actions of vitamin D are mediated by the vitamin D receptor (VDR), a protein whose gene sequence can vary, giving rise to polymorphic forms which are potent enough to affect the binding capacity of this protein to vitamin D. Some of these polymorphic forms of VDR gene may be associated with reduced effectiveness of vitamin D and hence predispose individuals to diseases such as type 2 diabetes and insulin resistance. An earlier study, the Surya Study, looked at the responsiveness of the South-Asian women living in Auckland to vitamin D. The research described here is an extension of this study and its focus was to identify the associations/linkages between certain polymorphic forms of the VDR gene and the disease conditions and intervention responsiveness in the same women. The first objective was to compare two well known techniques for genotyping single nucleotide polymorphisms (SNPs) of the VDR gene at the 3’ end, namely BsmI, ApaI and TaqI: the newer real-time polymerase chain reaction (qPCR) and the traditional restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) techniques. This comparison was performed to evaluate alternative methods for genotyping which consumed less time than RFLP-PCR. When the presence of each polymorphism by both the techniques was compared in this cohort of South-Asian women, it was found that RFLP-PCR proved to be a more reliable technique than qPCR for genotyping the VDR gene. Another objective of this project was to investigate the prevalence of the above three polymorphisms along with Cdx-2 and FokI SNPs which are present at the 5’ end of the VDR gene, in the population under study and their possible association with phenotypes such as vitamin D responsiveness and insulin resistance. These women were screened and biochemical data was collected during the earlier Surya Study. Of these, eighty-one women were then selected for intervention based on them having high insulin resistance (HOMA-IR>1.93) and serum 25(OH)D<50 nmol/L. Out of these eighty-one women, forty-two were given vitamin D supplement and thirty-nine were given a placebo for six months. Baseline and endpoint measurements included insulin resistance (HOMA-IR), insulin sensitivity (HOMA2%S) etc. How each individual responded to treatment in the intervention group was analysed in the context of the polymorphisms that they had. An association of insulin resistance with BsmI, ApaI and TaqI SNPs was observed in this cohort of 239 women. The response to insulin resistance in the vitamin D supplemented group significantly differed for FokI genotype compared to other genotypes. This explained why certain women responded to treatment better than the others. When the frequencies of the genotypes of these five SNPs of the VDR gene were compared to other studies of different ethnicities, the results of this study were consistent with few studies but contradictory to others. The possible reasons for these differences could be because of small sample size and different ethnicities under study due to which the frequency of alleles and hence the genotypes differed.

The metabolism of vitamin D commences with exposure of the skin to sunlight. The growing recognition of its role in insulin resistance, autoimmune disorders, infections, cancer, as well as the health of cells that influence physical and mental function have profound implications on how we define vitamin D requirements and why we should care whether they are met or not. Most of the actions of vitamin D are mediated by the vitamin D receptor (VDR), a protein whose gene sequence can vary, giving rise to polymorphic forms which are potent enough to affect the binding capacity of this protein to vitamin D. Some of these polymorphic forms of VDR gene may be associated with reduced effectiveness of vitamin D and hence predispose individuals to diseases such as type 2 diabetes and insulin resistance. An earlier study, the Surya Study, looked at the responsiveness of the South-Asian women living in Auckland to vitamin D. The research described here is an extension of this study and its focus was to identify the associations/linkages between certain polymorphic forms of the VDR gene and the disease conditions and intervention responsiveness in the same women. The first objective was to compare two well known techniques for genotyping single nucleotide polymorphisms (SNPs) of the VDR gene at the 3’ end, namely BsmI, ApaI and TaqI: the newer real-time polymerase chain reaction (qPCR) and the traditional restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) techniques. This comparison was performed to evaluate alternative methods for genotyping which consumed less time than RFLP-PCR. When the presence of each polymorphism by both the techniques was compared in this cohort of South-Asian women, it was found that RFLP-PCR proved to be a more reliable technique than qPCR for genotyping the VDR gene. Another objective of this project was to investigate the prevalence of the above three polymorphisms along with Cdx-2 and FokI SNPs which are present at the 5’ end of the VDR gene, in the population under study and their possible association with phenotypes such as vitamin D responsiveness and insulin resistance. These women were screened and biochemical data was collected during the earlier Surya Study. Of these, eighty-one women were then selected for intervention based on them having high insulin resistance (HOMA-IR>1.93) and serum 25(OH)D<50 nmol/L. Out of these eighty-one women, forty-two were given vitamin D supplement and thirty-nine were given a placebo for six months. Baseline and endpoint measurements included insulin resistance (HOMA-IR), insulin sensitivity (HOMA2%S) etc. How each individual responded to treatment in the intervention group was analysed in the context of the polymorphisms that they had. An association of insulin resistance with BsmI, ApaI and TaqI SNPs was observed in this cohort of 239 women. The response to insulin resistance in the vitamin D supplemented group significantly differed for FokI genotype compared to other genotypes. This explained why certain women responded to treatment better than the others. When the frequencies of the genotypes of these five SNPs of the VDR gene were compared to other studies of different ethnicities, the results of this study were consistent with few studies but contradictory to others. The possible reasons for these differences could be because of small sample size and different ethnicities under study due to which the frequency of alleles and hence the genotypes differed.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Umeå : Univ., 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Dissertation (Ph.D.).--University of Texas Graduate School of Biomedical Sciences at San Antonio, 2007. / Vita. Includes bibliographical references.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Bibliographical references: leaf 243-269.