Fabry disease: The importance of biology for screening and diagnosis

what you need to know ...

Fabry disease is a rare but potentially serious and under-diagnosed hereditary metabolic disorder
The damage caused by this disease is often multisystemic (renal, cardiac,
cerebrovascular, etc.)

Patients suffering from Fabry disease have a reduced life expectancy, averaging 20 years for men and 15 years for women.
Diagnosis is straightforward, and treatments are available to prevent irreversible damage.

Fabry disease is a genetic disorder linked to a mutation in the gene coding for alpha-galactosidase A (GLA) on the X chromosome, resulting in a deficiency of the lysosomal alpha-galactosidase A enzyme. This deficiency leads to the accumulation of intracellular glycosphingolipids (globotriaosylceramide or Gb3), and its deacylated derivative lyso-Gb3 or globotriaosylsphingosine), responsible for a multisystem disorder with dermatological, gastrointestinal, cochlear, renal, cardiac and neurological symptoms. These disorders are incurable and often associated with high morbidity and mortality in adulthood, in the absence of treatment.

Early diagnosis is therefore important in order to enable a specific treatment to be introduced, either enzyme replacement therapy or a chaperone molecule.

Definition - Epidemiology

Fabry disease is a lysosomal overload disease. It is a hereditary genetic disorder of glycosphingolipid metabolism, inherited on the X chromosome, due to a deficiency of alpha-galactosidase A.

Both men and women are affected. Heterozygous female carriers have a variable clinical phenotype, ranging from asymptomatic or pauci-symptomatic to severe forms, likely depending on their X chromosome inactivation (or lyonization) profile.

X chromosome inactivation or lyonization is a process whereby one of the two X chromosomes is randomly inactivated during embryogenesis in each cell.

This mechanism generates a mosaic of healthy cells (non-pathogenic variant of the activated GLA gene) and affected cells (pathogenic variant of the activated GLA gene) in varying proportions. The expression of a high percentage of the X chromosome carrying the pathogenic variant would result in the appearance of more severe symptoms in women in the tissue concerned.

A male affected by the disease will transmit the mutated X chromosome to all of his daughters and none of his sons.

A female driver has a 50% risk of passing on the mutated X chromosome, whatever the sex of her child.

Two disease phenotypes can be distinguished:

Classic form: Systemic disease with multivisceral involvement, beginning in childhood, associated with a significant reduction in quality of life and a high morbi-mortality rate (in the case of the natural evolution of Fabry disease in men, life expectancy is 40 to 50 years);
Later-onset form: Incomplete clinical picture, mainly cardiac. Thus, the diagnosis can be made in certain patients with hypertrophic cardiomyopathy (HCM) in adulthood, including those with arterial hypertension.

The incidence of the disease is estimated at 1/10,000 births (including late-onset forms).

Clinical signs of Fabry disease

In women with Fabry disease, symptoms develop later than in men, but are potentially just as severe. The average age of onset is 13 years for women and 9 years for men.

When should the diagnosis be made?

Asking the patient questions may point to Fabry disease as a possibility, if there are previously diagnosed cases or a family history of renal and/or cardiac and/or cerebrovascular disease, as well as early and/or unexplained deaths (sudden death due to hypertrophic cardiomyopathy).
In the event of symptoms suggestive of hypertrophic cardiomyopathy, observed as early as childhood, one or more of the following signs may be present:
- Neuropathic pain in the extremities (fingers, hands, toes and/or feet) of the acroparesthesia type, consisting of burning, discharge and very intense, painful attacks that may be accompanied by an inflammatory syndrome (previously known as “Fabry attacks”). These pains may be the first sign of the disease in children, and generally subside in adulthood.
- Intolerance to heat, sun exposure or physical exercise.
- Diffuse or isolated angiokeratomas (purple to black maculopapules that do not disappear under finger pressure, sometimes slightly keratotic), of variable topography but usually located in the genital area and mucous membranes.
- Unexplained fatigue.
- Digestive disorders (abdominal pain, nausea, diarrhoea/constipation, early satiety).
- Reduced sweating (hypohydrosis or anhydrosis).
- Corneal deposits (whorled cornea), usually asymptomatic, sometimes associated with corneal haze. These deposits are revealed by slit-lamp examination and are virtually pathognomonic of Fabry disease (after ruling out amiodarone or hydroxychloroquine intoxication).
Other warning signs (related to early organ damage)
- Renal damage: Microalbuminuria followed by proteinuria, or even reduced glomerular filtration rate (GFR).
- -Cardiac damage: Increase in hypersensitive plasma troponin, abnormalities visualised on 48 h ECG/Holter (shortened PR interval, atrioventricular block, arrhythmias, T-wave inversion, etc.), echocardiography (left ventricular hypertrophy, non-obstructive concentric hypertrophic cardiomyopathy, etc.), cardiac MRI (late enhancement after gadolinium in the posterolateral wall of the left ventricle due to fibrosis, decreased T1 mapping signal, increased T2 mapping signal).

The median delay in diagnosis is 14 years in men and 19 years in women. Such a delay has serious consequences for patient outcome.

Evolution after age 20

The following complications may develop:

Kidney damage, as evidenced by microalbuminuria followed by proteinuria (sometimes of nephrotic rank), with chronic renal failure, preceded by a period of glomerular hyperfiltration, which may become terminal (mainly in men, more rarely in women).
Neurological damage: One or more transient ischemic attacks (TIAs) or strokes in the absence of specific risk factors, as well as suggestive lesions on cerebral MRI (hypersignals of white matter preferentially periventricular, lacunae, microbleeds, dolichoectasia of large arterial vessels, damage to the pulvinar thalamic nucleus at an advanced stage).
Cardiac involvement: Cardiomyopathy, cardiac rhythm and/or conduction disorders progressing to heart failure in advanced stages.
Uni- or bilateral cochleovestibular involvement, with deafness, vertigo and tinnitus.
More rarely, obstructive respiratory syndrome.

Focus on cardiological damage

Fabry disease accounts for 1% of hypertrophic cardiomyopathies (HCM) in cardiology.

Left ventricular hypertrophy (LVH) is the most common cardiac sign, reported in 50% of men (and up to 88% after the age of 30) and in 20% of women by the age of 50, in the absence of appropriate management (cardiac damage usually occurs 10 years later in women).

Other cardiac changes may be observed: diastolic dysfunction, leading to dyspnoea, angina symptomatology due to endothelial damage, arrhythmia and valvular damage.

The main prognostic factor is the development of cardiac fibrosis, which can lead to rhythm and conduction disorders.

A consensus of European experts on the management of the cardiovascular manifestations of Fabry disease has recently been published (Linhardt A et al, Eur J Heart Failure 2020).

And the ESC recommends routine testing for Fabry disease in HCM in men over 30 and in women if diagnosis is suspected (Elliott PM et al. Eur Heart J. 2014).

Focus on renal involvement

Renal involvement in Fabry disease is the consequence of Gb3 accumulation in renal cells, leading to inflammation, fibrosis and progressive renal ischemia. Initial involvement progresses to chronic kidney disease (CKD) in 84% of men and 35% of women with Fabry disease, and, according to the REIN 2019 report, Fabry disease accounts for 0.3% to 1% of renal failures of undetermined etiology.

The risk factors associated with the onset of chronic renal failure are male gender, the depth of alpha-galactosidase deficiency, and the level of proteinuria.

The purpose of evoking a diagnosis of Fabry disease is to enable the initiation of treatment to avoid progression of the renal disease to end-stage renal failure.

Accordingly, in 2013, the European Renal Association (ERA) recommended that Fabry disease be investigated in men under 50 and women of all ages with unexplained chronic kidney disease.

Hypertension should not be considered an exclusion criterion, as 50% of Fabry disease patients have mild to moderate hypertension (mainly when GFR is less than 60 mL / min / 1.73 m2).

As the disease is under-diagnosed, it is estimated that one in every 400 kidney transplant patients have Fabry disease, which would represent more than 60 male kidney transplant recipients with Fabry disease in France.

In renal transplant patients with Fabry disease, the graft is not recolonised by the pathological process, and has normal enzymatic activity. However, cerebrovascular and cardiovascular complications may persist, and cardiac damage remains the leading cause of death in Fabry disease.

Diagnosis of Fabry disease

In male patients

Diagnosis is based on biochemical measurement of α-galactosidase A activity in leukocytes and/or on a drop of dried blood (blotting paper).

This assay is performed in a specialised laboratory. Enzyme activity is undetectable or <3% in classic forms of the disease. In later-onset forms, particularly in cases of exclusive cardiac involvement, residual activity of between 1% and 20% may be found. In fact, an α-galactosidase A activity level of <25% is considered “collapsed” in a male patient. Molecular confirmation of the diagnosis is essential, through targeted analysis of the gene encoding α-galactosidase A (GLA) (genotyping) and identification of the pathogenic variant (sequencing using the Sanger technique).

This will help to characterise the clinical form (classic versus late-onset), carry out a family investigation, and determine sensitivity (or otherwise) to the chaperone molecule.

Another diagnostic approach may be to request sequencing by NGS (Next Generation Sequencing), a new-generation sequencing technique known as genome-wide sequencing, i.e. within a panel of genes (including the GLA gene) by clinical orientation: For example, a panel of genes responsible for cardiopathies in the case of a cardiac point of call, or a panel of genes responsible for nephropathies in the case of renal impairment, etc. In this case, phenotypic analysis (biochemical assay of α-galactosidase A activity) is carried out a posteriori.

As with any genetic analysis, written informed consent is required from the patient.

New diagnostic approaches are being developed, such as the study of the exome (all protein-coding sequences of the genome), or even the whole genome (WGS for Whole Genome Sequencing), which are already used in research and diagnosis, within the framework of multidisciplinary consultation meetings organised by rare disease care networks (FSMR).

In all cases, the pathogenicity of the variant must be established in a reference laboratory or by the Fabry disease coordinating reference centre.

Thus, any finding of a collapsed level of α-galactosidase should lead to genetic testing. The assay of lyso-Gb3 (substrate of the deficient enzyme, increased in Fabry disease) classically accompanies the initial work-up.

In girls and women

The activity of α-galactosidase A may be normal, due to preferential inactivation of the mutated X chromosome. Diagnosis is also based on a plasma lyso-Gb3 assay (sometimes elevated), but only by studying the GLA gene can the presence of a pathogenic variant of Fabry disease be confirmed. In fact, plasma lyso-Gb3 may be normal in some heterozygous women. Urinary lyso-Gb3 is rarely used for diagnosis but can be useful for therapeutic follow-up (it tends to normalise under treatment).

Thus, for diagnosis in girls and women, if α-galactosidase A activity is deficient and/or plasma lyso-Gb3 is elevated and/or in cases of strong clinical suspicion, GLA gene genotyping should be performed.

Diagnostic workup: Additional tests

Once the diagnosis has been made, further investigations are recommended:

Nephrology: Determination of serum creatinine and estimation of GFR using the CKD-Epi formula in adults and the Schwartz formula in children, combined with measurement of the albuminuria/creatinuria ratio (ACR) and proteinuria/creatinuria ratio (PCR). Renal biopsy and/or ultrasound may be considered.
Cardiac: Resting ECG, trans thoracic echocardiography, 24 or (better) 48 h holter-ECG, hypersensitive troponin, NT-pro-BNP or BNP assays, cardiac MRI in adults.
Neurological: Brain MRI, neuro-psychological evaluation if necessary. Electroneuromyography (ENMG) is normal in Fabry disease, as small nerve fibres are affected.
Audiogram.
Ophthalmology: Fundus, slit-lamp examination, visual field if necessary.
Bone: Osteodensitometry.
Pulmonary: Pulmonary function tests.
Biochemical and haematological examinations: Renal and cardiac work-ups, blood ionogram and total plasma protein assay, fasting blood sugar, investigation of lipid abnormalities, phosphocalcic work-up, blood count, urinary work-up (ACR, PCR).

Family investigation

Once an index case has been diagnosed, a family investigation should be carried out.

In young boys, early detection is recommended, as specific treatment can be introduced as early as 7-8 years of age, if the family wishes.

A clinical genetics consultation is recommended in order to draw up a family tree, inform relatives and any couples at risk about Fabry disease, in particular about the possibility of prenatal or pre-implantation diagnosis.

Medicinal management of Fabry disease

Treatment is based on enzyme replacement therapy or a chaperone molecule.

Substitutive enzymotherapy uses either agalsidase alfa (Replagal®) at a dose of 0.2 mg/kg every other week, or agalsidase beta (Fabrazyme®), at a dose of 1 mg/kg every other week, administered by intravenous infusion. It should be started before the onset of irreversible damage such as stroke or renal or cardiac fibrosis lesions.

Migalastat (Galafold®), the only chaperone molecule with marketing authorisation for Fabry disease, is reserved for adult and adolescent patients aged 16 and over, who are carriers of sensitive pathogenic variants of the GLA gene, and is administered orally, at a dose of 123 mg of active ingredient, every two days, between meals.

These treatments can only be initiated after a favourable opinion from the Fabry disease reference centre, one of its competence centres, or a reference centre for hereditary metabolic diseases.

Symptomatic treatments specific to each organ are essential for improving patient quality of life and life expectancy, and must be combined with prevention and correction of any additional cardiovascular risk factors (hypertension, smoking, dyslipidaemia, diabetes, obesity).

Patient follow-up

Regular specialist follow-up is essential for men, women and children. It is essential, in particular, to determine the evolution of the disease, detect any new lesion damage and check the efficacy and tolerance of the specific treatment.

It involves a clinical, radiological and biological check-up, at least once a year for men and every two years for women.

This follow-up is carried out by the doctor in charge of the Fabry disease coordinating reference centre and/or a Fabry disease competence centre, in liaison with the attending physician.