Defining the role of cancer-risk genes in Type 2 diabetes pathogenesis

Over the past decade advances in genetics have resulted in considerable
progress in defining the pathogenesis of type 2 diabetes. The discovery of
several genes responsible for monogenic diabetes has given valuable insight
into the workings of the beta-cell and its regulation. This work has had
direct clinical impact through development of molecular diagnostic tools as
well as more individualised therapy for patients based on their genetic
diagnosis.
More recently genome wide association scans (GWAs) have uncovered some novel
variants that predispose (albeit through individually modest effects) to the
more common multifactorial type 2 diabetes.These discoveries are increasing our
understanding of diabetes by implicating defects in previously unassociated
pathways. One of the more interesting observations is that several of the
genes which influence risk of diabetes also play a role in the development of
certain cancers. This research aims to understand some of the mechanisms
involved in the diabetes-cancer overlap by focusing on the tumour-suppressor
gene (CDKN2A/B)(p16) where the evidence for this overlap is the greatest. The
case for focussing on the CDKN2A/B genes comes from genome wide association
study data and rodent models: CDKN2A/B (p16) were the closest protein-coding
genes to one of the novel Type 2 diabetes susceptibility loci uncovered by the
GWAs; secondly, rodent studies show that CDKN2A (p16) over expression leads to
the diabetes phenotype.
The work outlined in this research protocol will help us to understand some of
the fundamental processes involved in both diabetes and cancer. It could
improve clinical care by uncovering new therapeutic targets to manipulate
beta-cell function for the treatment of diabetes as well as providing
information on the potential oncogenic side-effects of manipulating some of
these disease processes.

·To perform clinical studies that assess glucose tolerance in individuals with
cancer-predisposing mutations in the CDKN2A gene (p16)(causing familial
melanoma)

The carriers of a CDKN2A (p16)-mutation will be invited for an oral glucose
tolerance test

This is a standard procedure undertaken by the chief investigator and the
research nurses at the Department of Endocrinology routinely; thus there is
vast amount of experience with these particular metabolic tests.

Subjects can consent to each test as they wish and can withdraw from any part
of the study at any time. If subjects wish to withdraw then stored biological
samples will be discarded and any coded link to clinical data will be removed.

Numbers to be recruited: 20 with predisposing CDKN2A (p16) mutations and 20
controls (partners or relatives without a CDKN2A (p16)-mutation). The sample
size estimate is based on experience from equivalent studies but the potential
exists to increase sample size through collaboration with other groups (and
would be the subject of separate ethics applications).
Potential benefit to patients: recruited subjects may benefit from taking part
in the study by learning of glucose tolerance abnormalities, *pre-diabetes* ,
that might otherwise not be tested for and diagnosed.

Protocol for OGTT sample collection and analysis:
·Participant attends the Department of Endocrinology 08:30 after 10 hour
overnight fast, subjects have been able to drink water
·Baseline clinical characteristics are collected: age, weight (Kg), height (cm)
and waist circumference
·A small intravenous cannula is placed in one antecubital vein to avoid
multiple venepunctures
·Baseline bloods are drawn for glucose and insulin
·Participant is asked to drink a standard 75g oral glucose drink over 2-3mins
·Blood sample then collected at 15*, 30*, 60*, 90*and 120min after oral glucose
drink to be analysed for glucose and insulin.
·Glucose samples are collected in 5ml grey fluoride oxalate vacutainer tubes:
samples for insulin are collected in 7ml orange serum collection vacutainer
tubes
·All samples are kept on ice and spun within 5 min of collection in a portable
centrifuge at 5000G for 3min
·2 X 1ml aliquots of separated serum are then kept on ice and stored in -80
freezers until batched for assay
·Participant is given a light breakfast at the end of the OGTT

The visit for an intravenous glucose tolerance test will last for 3.5 hours.The
cannulation sites may bruise and there is a small risk of infection which will
be minimised by the use of sterile procedures. Some pain will be experienced
during the insertion of the cannulae,
Participants may benefit from taking part in the study by learning of glucose
tolerance abnormalities,
'pre*diabetes', that might otherwise not be tested for and diagnosed.
There is no direct benefit to participants but they will benefit from a
pre*diabetes test.