The paper aims to assess the relationship between non-insulin-dependent diabetes mellitus (NIDDM) or type-2 diabetes and hypothyroidism in the ethnic population in Texas, USA. In the first part, as no record is available, a working evaluation was done on the prevalence of the two endocrine disorders in outpatients in Texas clinics, and in the second part, the potential health problems associated with the co-occurrence of the two disorders was discussed.
According to the Texas Department of State Health Services (2007), the Hispanic population, mostly comprising American-Mexican origin, accounts for 36% of the total population, and is just next to the Non-Hispanic whites. Nearly, 12-18% of the population was diagnosed with diabetes. Assessing high mortality associated with diabetes in this ethnic group, an epidemiological study was undertaken by using molecular markers specific to single nucleotide polymorphisms (SNP’s) located near insulin-dependent glucose and lipid homeostasis genes. In a typical analysis, hepatocyte nuclear factor 4α (HNF4α) specific traits were screened by Lehman et al. (2007, pp. 513-517) for evaluating the racial prevalence of NIDDM in elderly people in all ethnic and racial groups, including the Mexican-American cohorts in Texas. In a nationwide survey, Permutt, Wasson, and Cox (2005, pp. 1431-1439) in an overview of genetic lineage of NIDDM indicated that minority ethnic groups, including Hispanics, are 2-4 times more affected than the white individuals. Further, it was found that high body mass index (obesity) contributed significantly towards NIDDM in all ethnic groups. Among the endocrine disorders, hypothyroidism is next to diabetes, and an epidemiological survey was conducted to recognize the SNP’s associated with thyroid function in different races/ethnic groups in Texas (Samollow et al., 2004, pp. 3276-3284). Here, the basic level of thyroid-stimulating hormone (TSH), the thyroid hormones, T3 and T4, and thyroid hormone binding globulin (TBG/TG) were recorded in these randomized subjects. The thyroid function genes like TSH receptor and iodothyronine deiodinase (DIO1) were strongly linked with SNP’s, recognized in people of Mexican/Spanish origin. Although there is no published record of the prevalence of hypothyroidism in NIDDM in Texas, the present studies reveal that Mexican-Americans, who are the main Hispanic residents, have a high independent prevalence of both disorders. Since diabetes and hypothyroidism, particularly in obese people who are on a fatty diet, are linked and both manifest into lipid metabolism disorders, hyperlipoproteinemia, and hypercholesterolemia, it is possible that the majority of obese and diabetic Texan Hispanic people also suffer from hyperthyroidism and the consequent lipid metabolic disorders.
For genetic analysis of hypothyroidism, SNP’s for TSH-receptor, DIO1, DIO2, and T3-receptor beta genes are employed for polymorphic analysis. The genetic determinants of NIDDM are SNP’s for HNF4α, Calpain 10, Glucagon receptor, glucokinase, and several insulin actions’ (INS) genes. Both hypothyroidism and NIDDM are typically associated with an increased level of serum triglycerides. Hypothyroidism in a healthy person is linked with an increase in serum total cholesterol, low-density lipoprotein (LDL), and apolipoprotein A-1 (Samollow et al., 2004, p. 3276). These conditions stimulate hepatic tissue to produce glucose from fatty acids via gluconeogenesis and enhance insulin resistance, which means not allowing insulin to bind to the receptors so that glucose metabolism is prevented. As a result, it leads to hyperglycemia. Insulin resistance in the case of NIDDM provokes hypertriglyceridemia and hyperlipoproteinemia and increases the level of LDL. Therefore, hypothyroid conditions in NIDDM patients can bring about severe hyperlipoproteinemia and eruptive xanthomas, and rouleaux formation in RBCs. In simple words, these are fat deposits in blood cells, and when in excess, they start to erupt from ruptured skin (Park et al. 2005, p. 502-503). In this particular case study, plasma LDL, cholesterol, and triglyceride concentration were found elevated but HDL level was unchanged. Elevated plasma LDL was related to impaired clearance of LDL due to decrease LDL receptor expression. A decrease in lipoprotein lipase activity resulted in enhanced triglycerides. In another investigation (Chubb, Davis, and Davis, 2005, pp. 5317-5320), it was examined whether insulin resistance in diabetics modifies the association between thyroid dysfunction and lipid parameters. The study revealed the prevalence of one hypothyroidism incidence in twelve type-2 diabetic patients. Usually, these disorders lead to an increase in serum TSH content while causing high insulin resistance. Usually, a fasting glucose tolerance test is recommended for type-2 diabetes, but considering the implication on lipid disorder and thyroid malfunction, TSH levels were included in routine diabetes tests. This enhances markedly the lipid risk factors, which in turn increase the cardiovascular risk. Consequently, more severe conditions like hypertension, hyperinsulinemia, dyslipidemia, visceral obesity, hypercoagulability, and microalbuminuria may emerge. Thyroid disorders may also severely affect diabetes management, e.g. hypothyroidism may retard the insulin requirement by the patient. The hypothyroidism treatment medications like fenofibrate, levothyroxine, and hypoglycemia agents were found to bring the lipid status to normal in diabetic patients.
In conclusion, the Mexican origin people living in Texas, already with a high incidence of type-2 diabetes, may also have a high proportion of hypothyroidism. These endocrine malfunctions especially in obese people may cause lipid metabolism disorders, and consequently more serious problems like coronary heart disease.
References
Chubb, SAP, Davis, WA & Davis, TME 2005,’Interactions among Thyroid Function, Insulin Sensitivity, and Serum Lipid Concentrations: The Fremantle Diabetes Study’, Journal of Clinical Endocrinology & Metabolism, vol. 90, no. 9, pp. 5317–5320.
Lehman, DM, Richardson, DK, Jenkinson, CP, Hunt, KJ, Dyer, TD, Leach, RJ, Arya, R, Abboud, HE, Blangero, J, Duggirala, R & Stern, M 2007, ‘P2 Promoter Variants of the Hepatocyte Nuclear Factor 4 Gene Are Associated With Type 2 Diabetes in Mexican Americans’, Diabetes, vol. 56, pp. 513–517.
Park, JR, Jung, TS, Jung, JH, Lee, GW, Kim, MA, Park, K-J, Kim, DR, Chang, S-H, Chung, S & Hahm, JR 2005, ‘A Case of Hypothyroidism and Type 2 Diabetes Associated with Type V Hyperlipoproteinemia and Eruptive Xanthomas’, Journal of Korean Medical Science, vol. 20, pp. 502-505.
Permutt, MA, Wasson, J & Cox, N 2005, ‘Genetic epidemiology of diabetes’, Journal of Clinical Investigation, vol. 115, no. 6, pp. 1431-1439.
Samollow, PB, Perez, G, Kammerer, CM, Finegold, D, Zwartjes, PW, Havill, LM, Comuzzie, AG, Mahaney, MC, Goering, HH, Blangero, J, Folley, TP & Barmada, MM 2004, ‘Genetic and Environmental Influences on Thyroid Hormone Variation in Mexican Americans’, Journal of Clinical Endocrinology and Metabolism, vol. 89, pp 3276–3284.
Texas Department of State Health Services 2007. Texas Community Diabetes Surveys – Summary Report. Web.