Agalsidase-β should be proposed as first line therapy in classic male Fabry patients with undetectable α-galactosidase A activity.

Fabry disease (FD) is a rare X-linked lysosomal storage disease caused by mutations in the α-galactosidase A (GLA) gene leading to deficiency of α-galactosidase A (α-gal A). This results in progressive multisystemic glycosphingolipid accumulation, especially globotriaosylceramide (Gb3) and globotriaosylsphingosine (Lyso-Gb3). Enzyme replacement therapy with two recombinant enzymes, agalsidase-α and -β is approved for two different dosages. However, little is known about which enzyme is more effective in decreasing the metabolite load in male and female patients with the classic form of the disease. In this prospective observational study, 14 consecutive adult Fabry patients (10 males) with a classic GLA-mutation, were switched from agalsidase-α to agalsidase-β at the respective licensed doses. Lyso-Gb3 levels were measured before the switch and for a period of 12 months after the switch in dried blood spots by tandem mass spectrometry. Mean age at start of the switch was 36.7 ± 14 years. Plasma Lyso-Gb3 levels decreased from 27.2 ± 17.9 ng/mL before the switch to 16.8 ± 10.5 ng/mL after the switch (mean reduction of 30.1%; p = 0.004). The decrease was maximal in the subgroup of 7 male patients with no or very low residual enzyme activity (mean reduction of 40.4%). However, two females with high residual enzyme activity also showed a reduction >30% after the switch. In male patients, the reduction of plasma Lyso-Gb3 correlated negatively with the residual α-gal A activity: r = -0.803; p = 0.009. Agalsidase-β at licensed dose is significantly more effective than agalsidase-α to reduce Lyso-Gb3 levels in classic Fabry patients, and should be used as first line therapy in classic males with no residual enzyme activity