Anderson–Fabry disease is an X linked lysosomal storage disorder, resulting from a deficiency of the enzyme α-galactosidase A (a-Gal A) and subsequent cellular storage of the enzyme’s substrate globotriaosylceramide (Gb3) and related glycosphingolipids.1 Gb3 progressively accumulates in various types of cells including vascular endothelial cells, cardiac cells (including cardiomyocytes, smooth muscle cells, conduction system cells, valvular fibrocytes), renal cells and neural cells.2 3 Male individuals are primarily affected, but female heterozygotes may also display symptoms ranging in severity, possibly due to skewed X-chromosome inactivation.4

Cardiac manifestations of this multisystem disease may appear in childhood or in adolescents,5 and in adulthood they substantially contribute to morbidity and mortality.6 The unremitting accumulation of glycosphingolipids in virtually all cardiac structures can lead to a variety of cardiac signs and symptoms, ultimately impairing cardiac function.6 7 Recently, an MRI study in patients with Anderson–Fabry disease has demonstrated increased signal intensities and abnormally prolonged myocardial T2 relaxation times (MT₂RT) throughout the entire LV myocardium, in addition to left ventricular (LV) hypertrophy.8

In 2001, enzyme-replacement therapy (ERT) with recombinant a-Gal A became available in Europe for treatment of Fabry disease patients.9 10 Several studies have shown that ERT is able to reduce microvascular deposits of Gb3 from the kidneys, the skin and the heart.9^–11 However, evidence showing that ERT can be effective in preventing progression of LV hypertrophy and, in parallel, improving myocardial function is limited,12 13 and no studies investigating the long-term effects on cardiac performance have yet been published.

Our study aimed to prospectively assess the effects of agalsidase beta therapy on LV function and MT₂RT, as assessed by MRI, in patients with Anderson–Fabry disease treated for a mean duration of 45 months.

METHODS

Patients

The study group comprised 11 adult patients (eight men hemizygotes, three female heterozygotes) clinically assessed and diagnosed as having Anderson–Fabry disease, between September 2003 and July 2008. Diagnosis encompassed measurement of a-Gal A enzyme activity and, subsequently, analysis of the mutation in the a-Gal A gene. All patients were eligible to participate in this study, and written informed consent from all subjects and approval from our hospital ethics committee were obtained prior to inclusion. The patients were examined by means of a physical examination and MRI before the start of agalsidase beta therapy (study 1) and after a mean treatment duration of 45 (9) months (range 29–58) (study 2). ERT consisted of intravenous infusion of recombinant a-Gal A (agalsidase beta, Fabrazyme; Genzyme Corporation, Cambridge, Massachusetts) at a dose of 1 mg/kg body weight once every 2 weeks. The presence of Anderson–Fabry disease symptoms and use of antihypertensive drugs were recorded throughout the study. To assess the severity of disease, the Mainz severity score index was used.14

MRI technique

MR studies were performed using a 1.5 T MRI system (Gyroscan Intera, Philips Medical System, Best, The Netherlands) equipped with high-performance gradients (maximum gradient amplitude 30 mT/m, maximum slew rate 150 mT/m/ms). Images were acquired with a five-element cardiac phased-array coil using a vectorcardiographic method for ECG-gating and respiratory gating. After performing a survey scan, a breath-holding T2 weighted black-blood multiecho multishot TSE sequence with four different echo times (TE) was used to obtain images of the four-chamber horizontal long-axis plane for MT₂RT measurements. The following parameters were used: TR/effective TE, 1500/45, 60, 75, 90; matrix, 256×512; FOV, 400 mm; slice thickness, 10 mm; number of slices, 3; TSE factor, 23; flip angle, 90°; scanning time, 22 s for each slice, all breath holding, for a total acquisition time of 66 s. LV long axis and four-chamber horizontal long axis images were acquired using a breath-holding 2D balanced turbo field echo multiphase–multislice sequence (TR/effective TE, 2.8/1.4; matrix, 160×256; slice thickness, 10 mm; flip angle, 50°); subsequently, biventricular short-axis images were obtained using nine to 10 slices covering the left ventricle from the apex to the base for evaluation of LV mass. The total acquisition time ranged between 25 and 30 min for each study.

MRI analysis

Postprocessing was performed on a dedicated workstation (Viewforum, Philips Medical System, Best, The Netherlands). A first qualitative analysis was performed; however, changes in signal intensity were too subtle to be qualitatively detected. Therefore, a quantitative analysis was obtained. For evaluation of MT₂RT, fixed regions of interest were placed along the interventricular septum, apex and lateral walls on the first echo image and reproduced on the other echo images. MT₂RT was calculated using a linear least-square fit applied on the logarithm of myocardial signal intensity versus echo time according to the formula M(TE) = M_oe^−TE/T2_, TE being the echo time and M(TE) the averaged signal from all regions of interest of the corresponding TE image. LV wall thickness was measured at the level of the mid-septum. Analysis of LV mass was performed choosing the slice with the greatest cardiac diameter of the 2D-balanced turbo field echo multiphase–multislice acquisition in the biventricular short axis; subsequently, the endocardial and the epicardial borders were manually traced, carefully including the papillary muscles, on each end-diastolic and end-systolic frame for each of the 9–10 slices. In addition, LV ejection fraction (EF), was calculated for all patients with Anderson–Fabry disease, at baseline and after 45 months of agalsidase beta therapy.

Statistical analysis

Data are presented as mean values, with the corresponding standard deviation. Differences in LV parameters between the results from studies 1 and 2 were analysed using a Student t test for paired observations. A p value <0.05 was considered statistically significant. A linear regression analysis was used to evaluate the effects of length of therapy and age of patients on MT₂RT and left ventricular functional parameters.

RESULTS

Patients

The study group comprised 11 adult patients with genetically confirmed Anderson–Fabry disease. The mean (SD) age of the eight male and three female patients at the time of diagnosis was 35 (11) years with ages ranging from 22 to 54.

Biochemical and molecular studies at baseline

The median baseline a-Gal A enzymatic activity in males was 0.25 nmol/h/ml, and values ranged from 0.2 to 4.2 nmol/h/ml (normal range 4.0 to 21.9). Enzyme activity at baseline in the three females ranged from 2.1 to 4.2 nmol/h/ml. A causal mutation/deletion was identified in all patients included in this study.

LV functional parameters and myocardial T2 relaxation times

The main focus of this study was to compare LV functional parameters and myocardial T2 relaxation times measured at agalsidase beta baseline (study 1) and after a mean of 45 months ERT (study 2). A significant decrease in LV mass was observed 188 (60) g (range 118 to 313) versus 153 (47) g (range 99 to 240) (p<0.001), as assessed by MRI. At baseline, LV hypertrophy was demonstrated in eight patients, including the oldest female, and had normalised in two patients during ERT. In addition, a statistically significant reduction in LV wall thickness, 16 (4) mm (range 11 to 22) versus 14 (4) mm (range 9 to 22) respectively, was found (p<0.001). Furthermore, a significant reduction in MT₂RT was observed (p<0.001). The reduction was noted in all myocardial regions, that is interventricular septum 80 (5) ms (range 70 to 86) versus 66 (8) ms (range 50 to 79), apex 79 (10) ms (range 64 to 94) versus 64 (10) ms (range 47 to 80), and lateral wall 80 (8) ms (range 69 to 91) versus 65 (16) ms (range 43 to 85) (figs 1–3). No significant changes were observed when comparing LV ejection fraction results from both studies (64 (3)% (range 57 to 69) vs 65 (5)% (range 55 to 71), p: NS). A significant direct correlation was observed between the age of the patients and the variation in myocardial T2 relaxation times, in all myocardial regions (p<0.05); conversely, no significant correlation was observed between the age of the patients and the variation in LV functional parameters, between the two studies (p: NS). Furthermore, there was no significant correlation between the length of treatment and the outcome variables (ie, MT₂RT, LV wall thickness/mass and ejection fraction).

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Figure 1

Individual values of myocardial T₂ relaxation time (ms) at baseline and after 45 months of enzyme-replacement therapy, measured in the interventricular septum, in the study population.

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Figure 2

Individual values of myocardial T₂ relaxation time (ms) at baseline and after 45 months of enzyme-replacement therapy, measured in the apex, in the study population.

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Figure 3

Individual values of myocardial T₂ relaxation time (ms) at baseline and after 45 months of enzyme-replacement therapy, measured in the lateral wall, in the study population.

Clinical characteristics

Clinical characteristics of the patients at the time of studies 1 and 2 are shown in table 1. Anderson–Fabry disease symptoms at ERT baseline included peripheral neuropathic pain (n = 9), cornea verticillata (n = 9), proteinuria (n = 8), hypohidrosis (n = 7), angiokeratoma (n = 7) and abdominal pain (n = 5). After a mean agalsidase beta treatment duration of 45 months, neuropathic pain, hypohidrosis and abdominal pain had resolved in all patients reporting these symptoms at baseline. Angiokeratoma had disappeared in one out of seven patients, and proteinuria had resolved in five out of eight patients. Treatment had no effect on the occurrence of cornea verticillata. Two patients with ESRD requiring dialysis treatment at baseline successfully received a renal transplant during the study. Six patients received treatment with antihypertensive drugs (angiotensin-converting enzyme (ACE) inhibitors, calcium antagonist), three received acetylsalicylate, two were on lipid-lowering agents, and two received erythropoietin. The agalsidase beta infusion were generally well tolerated by all patients included in this study. Forty-five per cent (5/11) of patients developed antibodies during ERT; however, antibody formation did not interfere with the clinical outcome and showed a progressive decrease during the follow-up period.

DISCUSSION

The results of this prospective study demonstrate that in patients with Anderson–Fabry disease, a significant regression in cardiac hypertrophy, in association with a reduction in myocardial T2 relaxation times, can be achieved through sustained administration of ERT with agalsidase beta at 1 mg/kg every other week. Moreover, patients manifesting a variety of clinical signs and symptoms may benefit substantially, as demonstrated by the amelioration of symptoms in our patients.

Anderson–Fabry disease is a rare X linked progressive disorder of lipid metabolism, and until the advent of renal dialysis, transplantation and ERT, males with the classical form had a median survival of approximately 50 years.15 The males have low or very low levels of a-Gal A and progressive symptoms typically present in childhood or adolescence. The initial symptoms primarily reflect damage to the somatosensory and autonomous nervous systems, for example, intermittent or chronic peripheral neuropathic pain, decreased ability to sweat (with heat, cold and exercise intolerance) and gastrointestinal symptoms (eg, abdominal pain, diarrhoea).5 16 17 Ocular changes (cornea verticillata), skin abnormalities (angiokeratoma) and mild proteinuria also commonly occur. With age, progressive renal involvement in males leads to ESRD requiring dialysis or renal transplantation, and cerebrovascular events (stroke, transient ischaemic attacks) may occur in both genders.4 15 Cardiac manifestations include LV hypertrophy, valvular disease, conduction abnormalities leading to arrhythmias, congestive heart failure, coronary artery disease, myocardial infarction and ascending aorta dilation.6 7 18 19 In males with specific gene mutations and in females heterozygotes with low enzymatic activity, the clinical manifestations can be limited primarily to the heart. This “cardiac variant” is characterised by progressive severe LV hypertrophy that mimics an obstructive or non-obstructive hypertrophic cardiomyopathy.20

Increased signal intensity and prolongation of MT₂RT throughout the entire LV myocardium have recently been reported in patients with Anderson–Fabry disease.8 Based on these findings, it has been postulated that prolongation of MT₂RT might be related to biophysical and biochemical characteristics of the tissue. In this respect, myocardial water and lipid alterations have been reported as factors leading to abnormal prolongation of MT₂RT and increases in signal intensity.21 Studies have demonstrated the efficacy and safety of ERT in patients with Anderson–Fabry disease. In particular, Eng et al9 demonstrated in a placebo-controlled, double-blind study that agalsidase beta (1 mg/kg) resulted in a histological clearance of Gb3 deposits in myocardial endothelial cells; this effect was sustained over 54 months of therapy.22 Furthermore, Weidemann et al suggested that clearance of Gb3 due to agalsidase beta leads to a regression of LV hypertrophy, which was documented by echocardiography and confirmed by MRI.12 In this latter study, LV function improved after 12 months of therapy with a standard dose of agalsidase beta (1 mg/kg every other week), and improvements in myocardial function were more pronounced in the second 6 months of ERT administration. More recent studies demonstrated that ERT cannot profoundly influence disease progression and clinical outcome, in patients with an advanced stage of the disease.23 In particular, Banikazemi et al did not find any significant reduction in renal, cardiac or cerebrovascular events or deaths in a double-blinded comparison of agalsidase beta and placebo in 82 patients with Fabry disease.24 However, subgroup analysis suggested a significant reduction in renal dysfunction. There are also controversial results on the beneficial effects of ERT on LV mass or LV function.25 26 In particular, Koskenvuo et al recently demonstrated that 2 years of agalsidase beta therapy had only a minimal effect on cardiovascular morphology and function in a group of nine patients who had substantial cardiac involvement at baseline.13 Only end-systolic LV volume was reduced by 15% but numerous other measurements of cardiac dimensions, LV mass, diastolic and systolic LV function and haemodynamic parameters were unchanged.

Kovacevic-Preradovic et al reported no apparent improvement in cardiac changes in 29 patients with early-stage disease treated for 37 months with either agalsidase alfa (Replagal, Shire Human Genet. Ther., Cambridge, Massachusetts) or agalsidase beta, in a pooled data analysis; only diastolic function improved slightly.27 Changes in cardiac mass, as measured by MRI, were significantly reduced following 6 months of treatment with agalsidase alfa compared with placebo, in a recent study by Hughes et al.28 Furthermore, Vedder et al found significant decreases in LV mass in 21 patients after 12 months of agalsidase beta at 1 mg/kg every 2 weeks.29

In the present study in 11 patients with Anderson–Fabry disease, 45 months of ERT with agalsidase beta at 1 mg/kg resulted in a significant decrease in LV hypertrophy as expressed by a reduction in LV mass and LV wall thickness, and a significant decrease in MT₂RT. It is reasonable to presume that a reduction in myocardial Gb3 deposits resulting from sustained ERT accounted for the decrease in signal intensity and overall improvement in cardiac performance. Sustained treatment with adequate doses of enzyme is of particular importance as an in vitro study has shown that a relatively limited percentage of administered enzyme reaches the cardiac compartment.30 In agreement with our results, a registry survey by Beck et al demonstrated a significant reduction of LV mass after 18 months of agalsidase alfa therapy.31 In combination with the observations by Ohashi et al,32 the results of a recent study indicate that the negative effects of neutralising antibodies to agalsidase can be overcome by administering a higher dose of enzyme.29

The difference between our results and the unsatisfactory responses observed by Koskenvuo et al13 might be explained by the younger mean age of our patient population (ie, 35 years vs 41 years), further supporting the hypothesis that initiation of ERT earlier in the course of the disease is critical in preventing long-term complications.33

Several reports demonstrating reduced efficacy in patients with advanced cardiac disease back this theory.13 23 In such patients, it is not expected that ERT will reverse structural fibrotic changes in the heart. In addition, other factors such as pretreatment severity of renal disease involvement supposedly contribute to the variable effects of ERT on LV mass in patients with this microvascular disease.23 The present study has several potential limitations that should be considered, including the relatively small number of evaluated patients. The small sample size did not allow for determination of a threshold value of MT₂RT defining the absence or presence of cardiac involvement in Anderson–Fabry disease. The lack of histological correlation and the absence of a control group of untreated Anderson–Fabry patients are acknowledged as further limitations. However, we considered it to be unethical to deny ERT to a subset of patients.

Further studies in larger patient populations are warranted to confirm the results of the present manuscript. To our knowledge, this is the first MRI study reporting positive long-term effects of ERT on cardiac performance in patients with Anderson–Fabry disease.

CONCLUSIONS

The results of this study indicate that long-term therapy with agalsidase beta ERT at 1 mg/kg every 2 weeks was effective in significantly reducing LV hypertrophy, improving overall cardiac performance, and ameliorating clinical symptoms in patients with Anderson–Fabry disease at various stages of the disease.