Abstract

Diabetes mellitus is a leading cause of morbidity and mortality worldwide. The International Association of Diabetes Pregnancy Study Group (IADPSG) defines gestational diabetes mellitus (GDM) as fasting plasma glucose (FPG) ≥ 5.1 mmol/L, and/or 1-hour glucose value ≥ 10.0 mmol/L and/or 2-hour glucose value ≥ 8.5 mmol/Lat 24-28 weeks of gestation (WG).

Evaluating blood glucose status in early pregnancy may detect early GDM (eGDM) whichpermitsearly clinical intervention; this is important because by 24weeks of gestation, there are potential serious obstetric complications in cases of diabetes in pregnancy.

Diabetes mellitus is usually preceded by a pre-diabetic stage (fasting blood glucose 6.1 mmol/L to 6.9 mmol/L but lower than the diabetic state which is > 7.0mmol/L). Both genetic and environmental factors contribute to the development of type 2 diabetes mellitus (T2DM).The TCF7L2 SNP rs7903146 gene is strongly associated with T2DM.

The role of this gene in eGDM in the Buea population is not known. Early detection of the gene can be used to prevent the development of GDM and subsequently diabetes mellitus.

Seventy seven pregnant women at < 24 weeks of gestation were selected for this study. Fasting plasma glucose and body mass index were measured using standard methods.

Then molecular analysis of the alleles TCF7L2 SNP rs7903146 was performed using Polymerase Chain Reaction (PCR) and Restriction Fragment Length Polymorphism (RFLP) and the association between the alleles and eGDM determined.

Apart from diastolic blood pressure whose mean values were significantly different between the normal and prediabetic groups (P-value: 0.02), the mean values for body mass index, systolic blood pressure and age were not statistically different between the two groups.

Ethnicity, family history of diabetes and gestational age were not also associated with early gestational diabetes in this study population. This study showed a strong association of the TCF7L2 gene (rs7903146) genotype with eGDM in this study population (P-value: 0.013) while no association was observed between the allele types with eGDM (P-value: 0.63).

This finding suggests that pregnant women in Buea should be screened for this genotypes in order to prevent possible development of type two diabetes mellitus in those found to possess it.

CHAPTER ONE

INTRODUCTION AND LITERATURE REVIEW

1.1 Introduction

Diabetes mellitus is the common end-point of a variety of disorders of insulin production and/or insulin action resulting in hyperglycaemia with associated abnormalities of carbohydrate, fat, and protein metabolism (ADA, 2014; WHO, 2006).

The aetiology of diabetes is heterogeneous, but most cases of diabetes can be classified into two broad aetiopathogenetic categories: type 1 and type 2. However, the American Diabetes Association (ADA) classifies diabetes into: type 1 diabetes, type 2 diabetes, gestational, and acquired disorders (ADA, 2014).

Diabetes is a serious and costly disease and it is associated with acute and chronic complications that contribute to excess morbidity and mortality in individuals, especially in developing countries (IIF, 2005).

The prevalence of diabetes is increasing worldwide. Recently, 14.2 million people were estimated to be living with diabetes in Africa, projected to increase to 34.2 million by 2040 (IDF, 2015).

According to the International Diabetes Federation (IDF), over two-thirds of African people with diabetes remain undiagnosed, representing the highest global percentage of undiagnosed diabetes, placing patients at risk of developing harmful and costly complications (IDF, 2015).

Diabetic Keto Acidosis and hypoglycaemia are the most significant acute complications of diabetes and its treatment, and both complications pose a significant risk of morbidity and mortality.

When diabetes is not well managed, complications develop that threaten health and endanger life. Acute complications are a significant contributor to mortality, costs and poor quality of life.

Abnormally high blood glucose can have a life-threatening impact if it triggers conditions such as diabetic ketoacidosis (DKA) in types 1 and 2, and hyperosmolar coma in type 2 (WHO, 2016). Abnormally low blood glucose can occur in all types of diabetes and may result in seizures or loss of consciousness. It may happen after skipping a meal or exercising more than usual, or if the dosage of anti-diabetic medication is too high (WHO, 2016).

Over time diabetes can damage the heart, blood vessels, eyes, kidneys and nerves, and increase the risk of heart disease and stroke. Such damage can result in reduced blood flow, which when combined with nerve damage (neuropathy) in the feet, increases the chance of foot ulcers, infection and the eventual need for limb amputation.

Diabetic retinopathy is an important cause of blindness and occurs as a result of long term accumulated damage to the small blood vessels in the retina. Diabetes is among the leading causes of kidney failure (WHO, 2016).

Gestational diabetes (GDM) is a temporary condition that occurs in pregnancy and carries long term risk of type 2 diabetes (Bellamy et al., 2009).  The condition is present when blood glucose values are above normal but still below those diagnostic of diabetes (WHO, 2013).

Women with gestational diabetes are at increased risk of some complications during pregnancy and delivery, as are their infants. Gestational diabetes is diagnosed through prenatal screening, rather than reported symptoms.

The exact aetiology of GDM has not been fully discovered yet. Studies have shown that genetic predisposition and environmental factors play important roles in the pathogenesis of GDM (Tuei et al., 2010). Increased risk for type 2 diabetes in patients with history of GDM and of GDM in women with familial history of diabetes may suggest that GDM and type 2 diabetes share a common genetic and environmental background (Bellamy et al., 2009).

Gestational diabetes mellitus (GDM) is hyperglycaemia first detected during pregnancy (WHO, 2012) and is found to be associated with various maternal and perinatal outcomes (HAPO, 2008; Landon et al., 2011).It is caused by disorders in responsiveness to insulin and its secretion. I

t poses a life-long increase risk of metabolic syndrome and diabetes in future to mothers as well as increase risk of glucose intolerance, obesity and metabolic syndrome to their offspring (ADA, 2004).

Detecting GDM during pregnancy is important as it provides an opportunity to identify women at risk of short term and long term complications (Cheung et al., 2011). Studies have shown that early diagnosis and intervention can reduce adverse perinatal outcomes (Crowther et al., 2005; Landon et al., 2009; and Horvath et al., 2010).

In 2016, ADA suggested guidelines for the management of Gestational diabetes. They include;

1. Checking your blood sugar levels
2. Following specific dietary guidelines given by your doctor, dietician, or diabetes educator

• Exercising

1. Keeping an eye on your weight gain
2. Taking oral medication or insulin, if necessary

Prediabetes refers to a plasma glucose level that is above the normal range but not high enough to meet the diagnostic criteria of diabetes mellitus. (FPG of 6.1 mmol/L or higher but less than 7.0mmol/L (ADA, 2014))  It usually indicates a risk of conversion to type 2 DM (T2D) (ADA, 2016; Forouhi et al., 2007; Nathan et al., 2007).

Even though not all patients with prediabetes progress to full-blown T2D, recent epidemiological studies have shown that subjects with prediabetes have various forms of vascular complications associated with T2D before the diagnosis of DM, which are also associated with an increased risk of kidney disease and cardiovascular morbidity and mortality (Forouhi et al., 2007; Nathan et al., 2007; Platinga et al., 2010; Grundy et al.,2012, Ford et al., 2010). Such findings suggest that even prediabetes may be a leading cause of complications that are typically attributed to DM.

An estimated 470 million people will be diagnosed with prediabetes globally by the year 2030 (Tabak et al., 2012). In a meta-analysis study to determine the progression rate of pre-diabetes to diabetes, the incidence rate was found to be 35.6 per 1000 person-years (Moris et al., 2013). 

According to Centres for Disease Control and Prevention (CDC) USA, based on fasting glucose or hemoglobin A1c (HBA1c) levels, 35% of U.S. adults aged 20 years or older had prediabetes (50% of adults aged 65 years or older) in 2010 and applying this percentage to the entire U.S. population in 2010 yielded an estimated 79 million American adults aged 20 years or older with prediabetes (CDC, 2010).

A study carried out in Cameroon to evaluate the prevalence and risk factors of prediabetes among adults leaving in Yaoundé, the overall prevalence was 15.03% and was higher in female than males. Overweight, obesity and hypertension were the major risk factors. (Mandobet al., 2017).

In Cameroon, very little information is available about prediabetes yet worldwide, adults with pre-diabetes have an increased risk of developing T2DM (Gerstein et al., 2007). Early diagnosis of prediabetes is a fundamental strategy to prevent transition to diabetes (Selph et al., 2015).

The prevalence of type 2 diabetes is dramatically increasing and represents a worldwide growing health problem (Hu, 2011; IDF, 2011). Even in those individuals with prediabetes the risk for cardiovascular disease and total mortality is almost doubled (ADA, 2010).

Prediabetic status is also associated with microvascular complications (ADA, 2010).Finally, 5 to 10% of untreated prediabetic patients will develop diabetes each year (DPP, 2002). Yet, the same proportion may convert back from the prediabetic status to normoglycemia (ADA, 2010).

Still, up to now information on the impact of multiple gene loci as to the risk for prediabetes is limited (Zyriaxet al., 2013).

Genetic factors are very important in the pathogenesis of T2D (Ozougwel et al., 2013). There is undeniable evidence that genetic susceptibility to the disease is polygenic. As of 2011, genome-wide association studies (GWAS) have so far found more than 36 genes that contribute to the risks of T2DM (Herder and Roder, 2011).

Transcription factor 7 like 2 gene is one of the vast numbers of genetic loci implicated in the pathogenesis of diabetes (Grant et al., 2006). TCF7L2 gene is a key component of Wnt signalling pathway expressed in pancreatic B cells(Cauchi et al., 2006) and belongs to the high mobility group-box family as a transcription factor (Duval et al., 2000) that plays a crucial role in the maintenance of glucose homeostasis.

The TCF7L2 gene spans 215Kb on chromosome 10q25.3 and encodes a transcription factor that has been found to be associated with blood glucose homeostasis and plays an important role in the Wnt signalling. (Duval et al., 2000; Yi et al., 2005).

Studies have confirmed the association between TCF7L2 gene variant rs7903146 (C/T) and/or rs12255372 (G/T) and T2DM in various countries like England (Cauchi et al., 2006) and Tunisia (Palizban et al., 2012). However conflicting results have been reported from China (Guo et al., 2007) as well as the native population of North America (Saadi et al., 2008).

According to WHO (2013), diabetes mellitus is usually preceded by a pre-diabetic stage where fasting blood glucose is higher than normal (falls in the range 110 – 125mg/dL but lower than the diabetic state which is >126mg/dL).

Women with a history of GDM and in addition with familiar history of diabetes are likely to have type 2 diabetes (Herring and Oken, 2011). This suggests that GDM and type 2 diabetes share a common genetic and environmental background.

The TCF7L2 SNP rs7903146 gene is one of the most important genetic factors of type 2 diabetes, and it may also play a role in the pathophysiology of GDM. The role of this gene in eGDM in the Buea population is not known. Early detection of the gene can be used to prevent the development of GDM and subsequently DM.

This study attempted to determine the association of the rs7903146 gene variant of TCF7L2 gene and fasting plasma glucose in early pregnancy in Buea, South west region of Cameroon.

 Seventy seven pregnant women <24weeks of gestation were selected for this study using informed consent and a questionnaire. Fasting plasma glucose and body mass index were measured using standard methods. Then molecular analysis of the alleles TCF7L2 SNP rs7903146 was performed using Polymerase Chain Reaction (PCR) and Restriction Fragment Length Polymorphism (RFLP) and the association between the alleles and eGDM determined.

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