Enzyme Replacement Therapy in Fabry Disease

INTRODUCTION Fabry disease is an X-linked error of glycosphingolipid catabolism caused by the deficient activity of the lysosomal hydrolase α-galactosidase A (α-gal A) in tissues and fluids of affected hemizygous males; most heterozygous females have an intermediate level of enzymatic activity. The enzymatic defect leads to a systemic deposition of glycosphingolipids, predominantly globotriaosylceramide (Gb3), in body fluids and in the lysosomes of endothelial, perithelial, and smooth-muscle cells of blood vessels. Deposition also occurs in ganglion cells.

Clinical manifestations in classically affected hemizygotes (with absent α-gal A activity), include pain and paresthesias in the extremities, vessel ectasia (angiokeratoma) in skin and mucous membranes, and hypohidrosis during childhood or adolescence. Corneal and lenticular opacities are early findings. With increasing age, proteinuria and renal impairment lead to hypertension and uremia. Renal failure typically occurs in the third-fifth decades of life, and these patients need chronic hemodialysis and/or renal transplantation.

Atypical hemizygotes with residual α-gal A activity may be asymptomatic or have late-onset, mild disease manifestations primarily limited to the heart (the "cardiac variant"). Recently a renal variant has been identified too. Heterozygous females may have an attenuated form of the disease.The most frequent clinical finding in females is the characteristic whorl-like corneal epithelial dystrophy. They usually are asymptomatic, although rarely can be severely affected as hemizygous males.

In the kidney accumulation of glycosphingolipids appear in the sequence in endothelial and epithelial cells of the glomerulus and of Bowman's space, epithelium of the loops of Henle and in distal tubules till proximal tubules, interstitial histiocytes and fibrocytes. Lipid-laden distal tubular epithelial cells desquamate and may be detected in the urinary sediment.

Renal blood vessels may be involved progressively and extensively. An early finding is arterial fibrinoid deposits. Other histologic renal findings are severe arteriolar sclerosis, glomerular atrophy and fibrosis, pseudotubular proliferation of residual glomerular epithelium, tubular atrophy and diffuse interstitial fibrosis. Preliminary studies of enzyme replacement therapy demonstrate that periodic infusions of recombinant human α-galactosidase A are safe and effective in patients with Fabry disease.

The purpose of this study is to evaluate the long term efficacy of enzyme replacement therapy in patients with Fabry disease and renal involvement.

AIM Primary

• To evaluate the effect of enzyme replacement therapy on the rate of decline in the glomerular filtration rate (GFR, measured by inulin clearance) in Fabry patients with renal involvement
• To evaluate the biological activity of recombinant human galactosidase in terms of clearance of plasma Gb3 (that is directly correlated with renal endothelial glycosphingolipid clearance) Secondary

To evaluate the effect of enzyme replacement therapy on:

• 24-hour urinary protein excretion
• renal plasma flow (PAH renal clearance)
• glomerular perm-selectivity (fractional dextran clearances)
• end stage renal failure, kidney transplantation or death
• systolic and diastolic blood pressure
• cardiac anomalies (left ventricular hypertrophy, arrhythmias, conduction anomalies)
• cutaneous anomalies
• ocular anomalies DESIGN Twenty patients (males and females) with Fabry disease, and renal involvement, referred to the SMIMAF - Studio Multicentrico Italiano sulla Malattia di Anderson-Fabry - will be enrolled in the study.