Molecular Imaging in Fabry Disease of the Heart

Fabry disease (OMIM 30150) is caused by mutations in the gene (AGAL) encoding for the lysosomal enzyme α-galactosidase A. Diminished activity of this enzyme results in progressive accumulation of its substrate globotriaosylceramide (Gb3) in the lysosomes of various cell types, including vascular endothelial cells, cardiomyocytes, valvular fibrocytes, conduction cells. The involvement of the heart in Fabry disease results in rhythm disturbances, progressive hypertrophy and scarring of the left ventricle leading to diastolic and systolic dysfunction.

Conventional diagnostic methods such as electrocardiography, transthoracic echocardiography and even magnetic resonance imaging (MRI) are not sensitive enough to detect early damage to myocardial tissue in Fabry disease. Identifying subtle early changes, at a point when specific treatment may be optimized, is therefore an area of ongoing interest. Early perspectives on Fabry heart involvement concentrated on the left ventricular hypertrophy. Later the widespread use of Cardiac MRI introduced the role of fibrosis, as suggested by the appearance of late gadolinium enhancement (LGE) in characteristic areas of the myocardium. Most recently, detection of oedema by T2-weighted imaging and/or T2-mapping on MRI, as well as 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) scanning have pointed to the possibility of focal inflammation as a causative factor in progression of the myocardial disease to replacement fibrosis, with its attendant risk of fatal arrhythmia and cardiac decompensation. Whether the oedema signal on MRI sequences truly represents tissue inflammation in Fabry disease and whether LGE fully corresponds to replacement fibrosis remains unknown. Circulating markers of inflammation and immune activation are elevated in Fabry cardiomyopathy, but no fully specific marker has yet been found to correspond to either myocardial focal oedema or LGE.

Although MRI is important for diagnosis and risk stratification in patients with cardiac involvement in Fabry disease, findings such as LGE, myocardial oedema and native T1 mapping tell the clinician little that is specific about the underlying disease mechanisms. Moreover, early inflammatory changes may occur in Fabry disease before the manifestation of such abnormalities are detectable by MRI. By combining PET imaging of myocardial inflammation with detailed MRI assessments of cardiac function, structure and tissue characterisation, hybrid PET/MRI has the potential to offer a comprehensive non-invasive workup for patients with Fabry disease.

Previous work has shown that 68Ga-DOTA-(Tyr3)-octreotate (DOTATATE), a somatostatin receptor PET tracer used in oncology imaging, can be re-purposed to image inflammation in the cardiovascular system. This method could be of particular use in conditions associated with focal myocardial inflammation such as Fabry disease because of low physiological expression of somatostatin receptors in healthy heart muscle, and therefore low background PET signal. Here, the investigators will investigate the use of 68Ga-DOTATATE PET/MRI for identifying myocardial inflammation in patients with Fabry disease.