SCREENING FOR FABRY DISEASE IN TWO GREEK NEPHROLOGY DEPARTMENTS

Christos Paliouras1, Stamatia Kouzouka2, Konstantinos Roufas1, Giorgos Ntetskas1, Foteini Lamprianou1, Nikolaos Karvouniaris1,

Emmanouil Anastasakis1

1Nephrology Department of General Hospital of Rhodes, Rhodes , Greece2Nephrology Department of General Hospital of Kos, Kos, Greece

FABRY DISEASE

Rare, X-linked lysosomal storage disease of glycosphingolipids.

Deficient activity of the lysosomal enzyme alpha-galactosidase A (α-GAL A) results in progressive intracellular accumulation of the substrate (globotriaosylceramide/Gb3, globotriaosylsphingosine/lyso-Gb3).

GLA gene is located on the long arm of the chromosome X (Xq22).

>670 mutations/variants have been described with variable clinical expression.

Incidence: 1:40.000-1:117.000 live male births in general population. Higher according to recent newborn screening studies.

FABRY DISEASE

Slowly progressive, multisystem disease with a 4-decade natural history.

Classical form

Frequent in hemizygous males.

Very low α-GAL A enzymatic activity (0-10%), increased serum andurinary levels of Gb3, lyso-Gb3.

Characteristic clinical features (angiokeratomas, acroparesthesias,cornea verticillata, hypo- or anhidrosis) appear during childhood orearly adolescence.

At a later age patients suffer from renal disease (proteinuric CKD),cardiac disease (hypertrophic myocardiopathy, rhythm disturbances)or CNS complications (cerebrovascular strokes) with limited lifeexpectancy (fourth or fifth decade of life).

FABRY DISEASE

Attenuated forms of the disease (cardiac variant, renal variant)

Higher level of residual α-GAL A activity (15-30%).

Isolated organ involvement (more often cardiac disease) appearinglater in life, without early, specific symptoms of the adolescence.

Fabry disease in females

Although an X-linked disorder heterozygous females may also beaffected (random chromosome X inactivation).

Diagnosis requires genetic testing, since the level of enzyme’s activitymay be within normal range.

Variable phenotype (asymptomatic, milder form or delayed onset ofsymptoms).

Up to 20% with severe organ involvement at mean age of 46 years (adecade later than hemizygous men).

FABRY NEPHROPATHY

Accumulation of glycosphingolipids in all renal cell types appears early, before the onset of microalbuminuria.

Characteristic histologic lesion is podocyte vacuolization (on electron microscopy lysosomal inclusions-myeloid bodies, concentric, multi-lammelated bodies of zebra-like pattern).

Clinical symptoms

Isosthenuria.

Progressively aggravated proteinuria: microalbuminuria, overtproteinuria during the third decade of life, nephrotic syndrome in 9%of hemizygous men.

Level of proteinuria correlates with the rate of loss of renal function.

Without specific therapy rapid deterioration of kidney function(mean reduction rate of GFR 6,9 ml/min/year) leading to ESRD(before the fifth decade of life in men).

FABRY NEPHROPATHY

FABRY DISEASE: SCREENING STUDIES

Rationale for screening in Fabry disease:

Rare genetic disorder.

Nonspecific and highly variable phenotype.

In 5% of cases there is no family history (de novo mutations).

Delayed diagnosis (mean age of diagnosis has been estimated in 23 and 32 years of age for men and women, respectively, many years after the onset of symptoms).

Patients may benefit from specific enzyme replacement therapy, available since 2001 (recombinant enzymes, agalsidase-α and agalsidase-β, administered in biweekly i.v. infusions).

FABRY DISEASE: SCREENING STUDIES

Screening studies in high risk populations

Newborns.

Renal disease (CKD, ESRD undergoing HD, transplanted patients).

Cardiac disease (hypertrophic cardiomyopathy, premature atherosclerosis).

CNS disease (stroke, small fiber neuropathy, migraine, multiple sclerosis).

FABRY DISEASE: SCREENING STUDIES

Overall prevalence of individuals with a GLA gene variant was 0,62% (0,6% for men and 0,66% for women), while the prevalence of a definite diagnosis of the classical form was 0,12% (0,11% for men and 0,13% for women).

Among ESRD population the corresponding prevalence estimates were 0,30% and 0,11% respectively.

Revealed a high number of individuals carrying variants of unknown pathogenicity (enzyme activity>30%)

Van der Tol L, Smid BE, Poorthuis BJHM et al. A systamatic review on screening for Fabry disease: prevalence of individuals with genetic variants of unknown significance. J Med Genet 2014; 51: 1-9

Schiffmann R, Fuller M, Clarke LA et al. Is it Fabry disease? Genet med 2016; 18: 1181-1185

AIM OF THE STUDY

Identification of undiagnosed cases of Fabry disease among ESRD patients receiving hemodialysis or peritoneal dialysis.

MATERIALS AND METHODS

Eighty five adult patients (62 males and 23 females) suffering from ESRD undergoing hemodialysis (n=73) or automated peritoneal dialysis (n=12) were tested for the presence of a GLA variant. Mean age of our cohort was 59,4 years (min 24 years, max 85 years).

From each patient a dry blood sample (DBS) on filter paper was collected and sent to specialized laboratory for analysis.

In males α-GAL A activity was measured initially. In case of low enzymatic activity, GLA gene analysis by PCR amplification and genomic DNA sequencing was followed.

In females GLA gene was analyzed.

RESULTS

Two HD patients (2,4%) were found positive for carrying a GLA variant.

The first patient, a 72-year old female, was carrier of the missensemutation c.376A>G (p.Ser126Gly).

Her medical history included heart failure NYHA class IV secondary to ischemic heart disease, implantation of a permanent pacamaker, 2-year hemodialysis due to ESRD of unknown origin and two ischemic strokes. Unfortunately the severity of her clinical condition did not allowed us to further investigate her.

Analysis of her family tree revealed the presence of six relatives (four females and two males) carrying the same mutation. Clinical and laboratory work-up were completed in three females (53, 50 and 32 years old, respectively), revealing no specific findings of the disease.

RESULTS

The second patient was a 44-year old male undergoing chronic hemodialysis due to obstructive uropathy.

He was found carrying the GLA mutation c.937G>T (p.Asp313Tyr, D313Y). The residual enzyme activity was reduced (1,6 μmol/l/h, normal ≥2,6 μmol/l/h).

Further examination revealed the presence of white matter lesions on brain MRI as well as bilateral hypoacousia on audiogram. The patient was finally administered enzyme replacement therapy.

CONCLUSIONS

We identified two HD patients carrying the GLA gene variants p.Ser126Gly and D313Y.

The diagnosis of Fabry disease is still underestimated among ESRD patients.

Screening studies of high-risk populations are important for the detection of undiagnosed cases as well as for identifying affected family members.

Pathogenicity of some GLA variants such as p.Ser126Gly remains to be elucidated.

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