Advances in the treatment of Fabry disease

Fabry disease is a treatable disease, and management is now focused on enzyme replacement therapy, although oral pharmacological chaperone therapy seems a promising alternative treatment for patients with specific mutations

Francois Eyskens MD PhD

Department of Paediatrics

Division of Inherited Metabolic Diseases CEMA, University Hospital of Antwerp Antwerp, Belgium

Fabry disease (FD) is a rare X-linked inherited lysosomal storage disorder in which partial or complete deficiency of α-Galactosidase A (α-Gal) leads to progressive accumulation of metabolic intermediates, particularly globotriaosylceramide in many tissues.^1–3

More than 400 mutations for the a-Gal A gene are known.^4–6 Hemizygous males carry a defective X-chromosome and develop classical FD, whereas heterozygous females have one normal and one abnormal X chromosome and therefore usually have a later onset of disease than hemizygous males.^7–9

Patients with FD usually present in childhood and adolescence with neuropathic pain crises, acroparaesthesia, hypohidrosis, temperature intolerance, gastrointestinal symptoms, angiokeratoma, and corneal abnormalities.^10,11 Given the rarity of the disorder and the sometimes non-specific presentation, the diagnosis is often missed and misdiagnosis is common.¹² Severe morbidity and mortality follow in adult life due to renal failure, cardiac involvement, and stroke.¹³ Screening studies on the prevalence of FD in stroke patients (Belgian Fabry Study (BeFaS) and Stroke in young Fabry patients (SIFAP)) revealed a prevalence of 0.5–1% in this population at risk.^14,15

Rational of baseline assessment at diagnosis

The diagnosis of FD is made by measuring α-Gal enzymatic activity in lymphocytes in men and mutation analysis of the α-Gal A gene in men and women. Once the diagnosis of FD is confirmed, further investigations to assess of the severity of organ dysfunction is indicated in every patient, in order to select specific and adjunctive therapies and to provide the baseline against which the effectiveness of such therapies will be assessed.¹⁶

A specific severity score, such as the Mainz Severity Score Index, allows the medical team to integrate the results of the clinical assessment and additional investigations and allows sequential monitoring of overall disease severity.¹⁷

Recommended investigations for FD patients

General

Medical history and family pedigree
Clinical examination
Vital signs
Pain score (BPI)
Age appropriate Quality of Life score (SF-36 or EQ5D)
Severity Score Index – Mainz Severity Score Index.

Neurology

MRI brain examination
QSART assessment of sweating (where available)
EMG and quantitative/qualitative sensory testing.

Cardiac

ECG
24 hour ECG
Echocardiogram
Exercise testing
Blood pressure.

Renal

Glomerular filtration rate/creatinine clearance
24 hour urine total protein/microalbumin (or morning sample mg/g creatinine)
Renal biopsy (at the discretion of the renal physician).

Ophthalmology

Slit-lamp examination (cornea verticillata)
Retro-illumination (cataract)
Fundoscopy (vascular abnormalities)

Audiology

Pure tone audiogram
Brainstem-evoked potentials – at the discretion of the neurologist
Vestibular examinations

Bone disease

DEXA scan

Laboratory investigations

Full blood count
Urea and electrolytes
Liver function tests
Fasting lipid profile
Plasma Gb3/lyso-Gb3
Urine Gb3/lyso-Gb3

Genetic family screening¹⁸

Treatment

Enzyme replacement therapy

Two enzyme formulations are licensed in Europe by the European Medicines Agency for the treatment of FD: agalsidase alfa (Replagal^®, Shire Human Genetic Therapies) at a dose of 0.2mg/kg intravenously over a period of 40 minutes every two weeks; and agalsidase beta (Fabrazyme^®, Sanofi-Genzyme Corporation) at a dose of 1mg/kg intravenously over a period of up to four hours every two weeks. Agalsidase beta was approved by the US Food and Drug Administration in 2003.

Agalsidase alfa is produced using a genetically engineered human fibroblast cell line. Agalsidase beta is produced using a Chinese hamster ovary cell line. The product licences are based on the National Institute of Health (NIH) study using agalsidase alfa¹⁹ and the trial using agalsidase beta conducted by the Mount Sinai School of Medicine study group.²⁰

Both studies were randomised, double-blind and placebo-controlled. Treatment with algalsidase alfa has also been shown to stabilise renal function, cardiac abnormalities and pain;^21,22 to improve quality of life; and to improve hearing.²³ Treatment with agalsidase beta has been shown to improve cardiac function²⁴ and renal function.²⁵ A Phase IV randomised double-blind trial of agalsidase beta showed a reduction in clinical progression of the disease in treated patients with respect to renal, cardiac and central nervous system events.²⁶

The safety of enzyme replacement therapy (ERT) in young children has been demonstrated in two clinical trials. A clinical trial of algalsidase alfa in children aged 2–18 years was performed. During the six-month study the drug was well tolerated. The pain scores improved or were unchanged from baseline in 12 of 13 patients. All patients continued on ERT at the end of the clinical trial.¹⁷ In the second international, open-label study, children with FD were treated with 1.0 mg/kg agalsidase beta biweekly. ERT was well tolerated; there was superficial dermal capillary GL-3 clearance and gastrointestinal symptoms showed statistically significant improvement.²⁸

Antibody production has been reported with both preparations but there is no clear evidence of any impact on clinical efficacy of treatment.^29,30 IgE antibodies are less common and have not been observed in patients receiving agalsidase alfa.

There are no data available on the appropriate starting time of treatment or the group of patients most likely to benefit from therapy. However, because FD is a chronic and progressive disorder, the aim of treatment is to prevent progression, and where disease is already manifest, to try and reverse or stabilise the disease. It is anticipated that treatment will be most successful when started early in the course of the disease. In males, treatment should commence as soon as symptoms of FD appear. In females, the presence of a pathogenic mutation alone is not an indication for ERT; however, criteria for commencing therapy in females should be the same as those in males.³¹

Indications for initiation of ERT

Treatment with ERT is indicated in patients who have any of the following features shown in Table 1.³²

Exclusion criteria for ERT

Exclusion criteria for ERT include:

The presence of another life-threatening illness with a life expectancy of < one year
End-stage FD patients who are deemed too severely affected to benefit from ERT (for example, severely incapacitated following cerebrovascular disease).

Adverse events of ERT

Adverse events should be categorised into infusion- and non-infusion-related adverse events and should be scored as mild, moderate or severe. In case of failure to change in symptoms or lack of efficacy, especially deterioration of proteinuria and decline of GFR, the measuring of α-Galactosidase A (neutralising) antibodies may be considered.

Stop criteria for ERT³²

Non-compliance
Persistent life threatening or severe infusion reactions that do not respond to prophylaxis
End-stage renal disease, without an option for renal transplantation, in combination with advanced heart failure
Lack of response on neuropathic pain.

Pharmacological chaperone ERT

The use of the oral pharmacologic chaperone, migalastat (Galafold^®, Amicus), acting as active-site inhibitor, has been shown to promote the refolding and correct trafficking of mutant α-Gal in the presence of residual enzyme activity (amenable mutations-missense mutations).

Galafold is licensed in Europe for the treatment of FD above the age of 16 years based on the data of two Phase III studies:

011FACETS: a randomised, placebo-controlled, study of treatment naïve patients with FD and kidney involvement. The primary endpoint, namely the clearance of interstitial capillary GL-3 inclusions, was not reached due to inclusion of 17 patients with a non-amenable mutation in the study.³³ However the clinical efficacy of migalastat on the kidney was clearly demonstrated: annualised eGFRCK-D-EPI remained stable over an average of 36 months (Study 011+ extension, n=40). The annualised rate of change over this period was: –0.81 ml/min/1.73 m²/year (95% CI: –2,00–0.37). This long-term effect of migalastat on eGFR is comparable to the decline over time in healthy adults (approximately –1 ml/min/1.73m²) and the decline over time in FD patients treated with agalsidase beta.²⁵
012 ATTRACT: a randomised (1.5:1) open-label, active-controlled, study of ERT-treated patients with amenable (responsive) mutations switched to migalastat compared to the control group who remained on ERT of 18 months’ duration. The primary objective of the study was to determine the comparability of migalastat to ERT in their effects on renal function: this primary endpoint was reached. Left ventricular mass index (LVMi) decreased significantly with migalastat treatment while there was no significant change with ERT (secondary endpoint). The composite outcome included cardiac, renal, and cerebrovascular events associated with morbidity and mortality in FD: the proportion of patients who had an event was 29% (10/34) in patients switching from ERT to migalastat and 44% (8/18) in those remaining on ERT.³⁴

Migalastat was generally safe and well-tolerated, as shown in the Phase III studies and extensions.

Adjunctive therapies

Adjunctive therapies include treatment of pain, gastrointestinal symptoms, angiokeratoma, primary and/or secondary prevention of organ disease (stroke, renal failure, cardiac disease). These therapies should be available to all patients who are symptomatic.

For adjunctive treatment, there are no randomised controlled trials of these therapies in FD and the evidence for their effectiveness is largely derived from experience in other conditions (Grade C, evidence level IV).

Pain

Chronic pain: anticonvulsants (for example, carbamazepine, gabapentin, topimarate)
‘Fabry crises’: non-steroidal anti-inflammatory drugs, opiates, minimisation of activities that trigger painful crisis (for example, temperature changes, physical activity, stress).

Angiokeratoma

If desired by the patient: removal with argon laser therapy.

Gastrointestinal symptoms

Low-fat diet
Small and frequent meals
Motility agents.

Cerebrovascular and cardiovascular disease

Rigorous control of arterial hypertension, preferably by an ACE inhibitor (avoid β-blockers if sinus bradycardia is present)
Correct hyperlipidaemia: diet,
statins
Antithrombotic drugs: aspirin, aspirin + dipyridamole or clopidogrel
Smoking cessation
Correct obesity
Treatment of cardiac arrhythmia: antiarrhythmics, anticoagulants, ICD, pacemaker
Screening and treatment of coronary and/or carotid insufficiency
Heart transplantation.

Renal disease

Proteinuria: ACE inhibitor and ‘sartans’
Renal failure: dialysis and renal transplantation.

Psychological

Neuropsychiatric medication/psychotherapy.

Goals of FD treatment

The goals of FD treatment include an improvement in, or a prevention of deterioration in³⁵:

Renal function

Patient subgroup ≥90 and ≤ 135ml/min/1.73m²: GFR decline ≤ 1ml/min/1.73 m²/year
Patient subgroup <90ml/min/1.73m2: GFR decline ≤2ml/min/1.73m²/year for men and ≤1ml/min/1.73m²/year for women
Subgroup proteinuria >0.3g/day: no increase in proteinuria
Subgroup proteinuria ≥1g/day: reduction of proteinuria to <1g/day.

Cardiac structure and function

Cardiomyopathy (LVMi >51g/m^2.7 in men and >48 g/m^2.7 in women (LVM indexed to height): reduction of LVM into the normal range
Improve heart failure
Reduction in frequency and severity of rhythm disturbances.

General

Improve age-appropriate quality of life measurement
Reduced pain scores
Reduce incidence of ischaemic stroke
Normalise growth and development in children.

Key points

Fabry disease (FD) is an X-linked inherited multi-systemic lysosomal storage disease.
Early diagnosis is essential in order to provide appropriate and timely treatment.
Awareness of the possibility of this disease must be increased among paediatricians, internal medicine physicians, neurologists, ophthalmologists and ENT specialists.
FD is a treatable disease, and management is now focused on enzyme replacement therapy, although oral pharmacological chaperone therapy seems a promising alternative treatment for patients with specific mutations. Adjunctive therapies, including antithrombotic agents to prevent stroke and ACE/’sartans’ in case of proteinuria, are also very important in the management of these patients.
There is a need of collect further outcome survey data (registries) and for comprehensive guidelines for optimising and standardising the diagnosis and treatment of FD patients.

References

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Advances in the treatment of Fabry disease

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