The molecular genetics of Type 2 diabetes.
Type 2 diabetes has a substantial genetic component. The aim of this
dissertation was to investigate the molecular basis of Type 2 diabetes with
particular emphasis on the role of the glucokinase gene. Other work studied
specific mutations in the tRNALeu(UUR) gene of mitochondrial DNA and in the
glucagon receptor gene.
The Introductory chapter presents an overview of Type 2 diabetes, and the
influence of the environment and the contribution of genetics to its development.
It then introduces the molecular biological approach to the study of this disease
and the function of the J3-cell and the important role of glucokinase in glucose
Chapter 2 gives details of ascertainment criteria for the subjects studied and
outlines the methodology used to study the molecular genetics of Type 2
diabetes. The techniques described include DNA extraction, the polymerase chain reaction (PCR), microsatellite markers, restriction fragment length
polymorph isms (RFLPs), mutation screening, separation of PCR products and
direct sequencing of them.
Chapter 3 investigates the role of the glucokinase gene in five pedigrees with
maturity onset diabetes of the young (MOOY). Using the microsatellite
polymorph isms GCK1 and GCK2, diabetes was found not to be linked to the
glucokinase gene in these multi-generation pedigrees.
Chapter 4 assesses the contribution of the glucokinase gene to Type 2 diabetes
in the UK Caucasian population by investigating the two microsatellite
polymorph isms in well-characterised Type 2 diabetic subjects and
normoglycaemic control subjects. There was no linkage disequilibrium between
the two polymorphisms, and no association with diabetes was found. This
suggests that a single mutation in or near the glucokinase gene is not a common
cause of Type 2 diabetes in this population.
Chapter 5 describes the development of a robust method to screen for mutations
using the technique of single-stranded conformational polymorphism (SSCP)
analysis. Chapter 6 utilises this method, and found that mutations in the
glucokinase gene can contribute to the pathogenesis of gestational diabetes.
Four pedigrees from the Oxford district had been found to possess the same missense mutation in the glucokinase gene at position 299. Chapter 7
establishes that the high prevalence of this glucokinase mutation in this district is
probably due to a founder-effect, by haplotyping affected members of the four
pedigrees for GCK1 and GCK2.
Chapters 8 and 9 use restriction fragment length polymorphism (RFLP) analysis
to detect specific mutations known to create, or remove a cutting site for a
restriction endonuclease. Chapter 8 investigates the contribution of the
mitochondrial transfer RNA (tRNALeu(UUR) mutation at position 3243bp to Type 2
diabetes. Chapter 9 studies a mutation in the glucagon receptor and its possible
susceptibility to Type 2 diabetes.
Chapter 10 concludes the dissertation and outlines future areas for investigation.