Defining the Functional Effects of Titin Gene Mutations on the Pathophysiology of Dilated Cardiomyopathy and their Clinical Significance

Heart failure affects over 750,000 people in the UK. Dilated cardiomyopathy (DCM) is the second commonest cause and occurs in up to 1 in every 500 people.

What is dilated cardiomyopathy?
Dilated cardiomyopathy is a condition where the heart muscle becomes weaker (cardiomyopathy) and the heart becomes bigger (dilated). People can develop problems with fluid on their lungs, dangerous heart rhythms, and in some cases, ultimately a heart weak enough to need replacing with a transplant.

In the vast majority of cases, we do not fully understand what causes the damage to the heart in the first place. This means that we do not have any targeted treatments to offer these patients. We currently use the same medicines in all patients with weak heart muscle, whatever the cause.

Unfortunately, people with this condition may not have any symptoms until very advanced stages of the disease which means that the treatment we do have may not be able to do very much to repair or halt the damage to the heart.

What is this research trying to achieve?
Recent work done by researchers in our group, working with collaborators at Harvard University, has shown that a quarter of people who we previously thought had no identifiable cause for the weak heart, had an abnormality in a gene (called TTN) responsible for making the biggest protein in heart muscle (titin). We would like to study in more detail what it means for people who carry this gene.

Who is doing this research?
This work is a collaboration between the cardiac MRI imaging department at the Royal Brompton Hospital and the genetics team at the Royal Brompton and Imperial College in London.
Together, Imperial College and the Royal Brompton Hospital form the largest specialist heart and lung centre in the UK. They have an internationally renowned research reputation and are best placed to conduct this research. The discovery of the abnormal gene (TTN) that forms a key part of this research was done in collaborative work by one of the research supervisors.

How are we going to do this research?
We would like to use an advanced scan of the heart called cardiac MRI to see if there is a pattern of disease in the heart muscle of patients with the abnormal gene.

We will invite our patients who we know have both dilated cardiomyopathy and the abnormal TTN gene to have an MRI scan of their heart. MRI scans of the heart are very good at looking at the detailed structure of the heart muscle and can pick up changes that other tests (for example echocardiograms) cannot. MRI scans are safe, non invasive and painless tests. On the MRI scan, we will look for early signs of disease such as scarring in the heart - called fibrosis and abnormalities in the blood supply (microcirculation).

We know that the abnormal gene can run in families so we will also invite the relatives of people with dilated cardiomyopathy to be tested for the abnormal gene. If they have the abnormal gene we will offer them the opportunity to have an MRI scan of their heart to see if they have any subtle changes in their heart, even when they do not have any symptoms.

Why is this important?
Crucially, once we have done the detailed MRI scan, we will also follow up the patients with dilated cardiomyopathy to see if we can identify any particular patterns in their genes or scans that are associated with a worse outcome in the long term. If this is the case, then we may be able to offer these patients earlier and more intensive treatment in the future to help prevent them from ending up with severe disease and this information might also help us to develop new treatments.

For those people who feel well but have been told they have the abnormal gene, we will see if there are any early signs of heart disease on their scans. If this is the case, then in the future, we may be able to start them on the right treatment sooner to avoid progressing to advanced disease and keeping their hearts healthy.

Background: Dilated cardiomyopathy (DCM) is the second commonest cause of heart failure and the leading indication for heart transplantation in the UK. Collaborative work from our group has shown that 25% of familial cases of 'idiopathic' DCM have a mutation in the TTN gene that encodes titin, the largest sarcomeric protein, which has key roles in the contractile process.

Aim: To define the functional effects of the TTN gene mutation on the pathophysiology of DCM and evaluate what clinical significance this mutation holds.

Objectives
1.Produce detailed phenotypic characterisation of DCM patients with TTN mutations by cardiac MRI (CMR). Determine if clear genotype/phenotype correlation.
2.Integrate genetic and CMR markers to determine prognostic significance of presence/type of TTN mutation in DCM.
3.Identify CMR early myocardial tissue markers of disease in TTN gene-positive/phenotype-negative patients (G+/P-).

Methodology
1.CMR: Scanning of DCM/TTN positive patients, including assessments for myocardial strain, interstitial fibrosis and late enhancement to look for replacement fibrosis. Assessment for microvascular ischaemia using Hybrid-EPI quantitative perfusion analysis in TTN G+/P- individuals

2.Genetics: Construction of DNA libraries. Comparison between patients with truncation and single amino acid missense non truncation mutations in the TTN gene.

3.Epidemiological Analysis of Outcomes: Prospective follow up (questionnaires, primary care & hospital records, Office of National Statistics' flag and track mortality). Statistical comparisons to determine if presence/type of TTN mutation is independently associated with outcome.

Scientific and Medical Opportunities of the Study
-Benefit for DCM patients, cardiomyopathy researchers, and pharmaceutical industry.
-Improved clinical monitoring of DCM patients and guided genetic counselling of their family members.
-Future development of novel therapeutic targets in G+/P- individuals.

The greatest potential benefit of this research will be for patients with dilated cardiomyopathy (DCM). Currently these patients may be diagnosed with dilated cardiomyopathy but have little understanding of how their disease will progress over the following years.

This research has the potential to add to how we manage these patients. By demonstrating any clinical significance with the presence of the TTN mutation, in the future we might be able to offer patients an individual risk profile of sudden death, based on their cardiac MRI results and genetic profiling, which will help to direct their management strategy which may include anything from medicines to invasive ICD (implantable cardiac defibrillator) implantation to reduce the risk of sudden cardiac death.

There will also be significant benefit to the relatives of patients with DCM and the TTN mutation. The mutation can run in families but at present, we are unsure what the significance of the mutation is in otherwise well people.

A common question asked by individuals identified with a TTN mutation is 'What does it mean?' The absence of early markers of disease when TTN positive can contribute to significant stress and anxiety amongst these individuals.

Through this research we hope to address this uncertainty, meaning that these people can be managed
appropriately. This will either mean reassurance if the presence of the mutation is not associated with scar changes on the cardiac MRI, or advising regular surveillance if the mutation is associated with early changes in heart structure that are not picked up on current imaging techniques.

As heart failure death is one of the leading causes of death in the UK, any changes to the overall risk of death in this disease, however small, will have a considerable national health benefit.

Given the speed with which the cost and turnaround time for genetic testing has fallen with Next Generation Sequencing platforms, it would be realistic to envisage mainstream clinical benefits of this work within a 5 year timeframe.

The private sector also may benefit from this research, providing support for the development of commercially viable TTN gene testing for use in the NHS.

Clinicians will also reap benefits through better risk stratification of their patients, developing targeted monitoring for the highest risk individuals and discharging those not affected. For example, in recent work from the Unit (Gulati et al, 2013), it was demonstrated that the presence of fibrosis in DCM was associated with a five-fold greater risk of sudden death and importantly with a net reclassification improvement index of 0.25 for stratification to defibrillator therapy (ICD). If implemented in routine practice, health economics data indicated that potential savings to the NHS through better patient selection for an ICD would amount to £2.5 Million per year.

This has population level implications for the allocation of resources and potentially increases the cost-effectiveness of medical therapy. This will also help to tailor NHS resources, including the costs of regular clinician follow up, medication, and MRI scanning, to the most appropriate population. Dr Prasad has an ongoing collaboration with the health economist Prof Jo Lord, at Brunel. Potential beneficiaries would therefore include health economists as an economic analysis could then have the potential to inform NHS policy.

On a personal level, I will benefit immeasurably from this research. In addition to the clinical and research project specific skills I will gain, I will also gain transferable generic skills which could be applied in all employment sectors as a Clinician-Scientist, namely skills in project management, leadership, organisation, and time management. I will gain experience in managing databases, resources and budgets. I will also build upon verbal and written communication skills honed in the dissemination of research outcomes.