Fabry disease is a progressive, X-linked inborn error of glycospingolipid metabolism caused by a deficiency in the lysosomal enzyme α-galactosidase A (α-Gal A) as a result of mutations in the α-Gal A gene (GLA). Despite being an X-linked disorder, females can express varying degrees of clinical manifestations. Fabry is a rare disease with incidence estimated between 1 in 40,000 males to 1 in 117,000 in the general population. Moreover, there are variants of later-onset phenotype of Fabry disease that can be under-diagnosed, as they do not present with classical signs and symptoms. This, and the study of newborn screening for Fabry disease, suggests that the actual incidence of Fabry disease can be higher than currently estimated.
Clinical manifestation of the disease can correlate with residual α-Gal A levels. Untreated, life expectancy in Fabry patients is reduced and death usually occurs in the fourth or fifth decade because of vascular disease affecting the kidneys, heart and/or central nervous system. The enzyme deficiency leads to intracellular accumulation of the substrate, globotriaosylceramide (GL-3) in the vascular endothelium and visceral tissues throughout the body. Gradual deterioration of renal function and the development of azotemia, due to glycospingolipid deposition, usually occur in the third to fifth decades of life, but can occur as early as in the second decade. Renal lesions are found in both hemizygous (male) and heterozygous (female) patients.
Cardiac disease occurs in most males and many females. Early cardiac findings include left ventricular enlargement, valvular involvement and conduction abnormalities. Mitral insufficiency is the most frequent valvular lesion typically present in childhood or adolescence. Cerebrovascular manifestations result primarily from multifocal small-vessel involvement and can include thromboses, transient ischemic attacks, basilar artery ischemia and aneurysm, seizures, hemiplegia, hemianesthesia, aphasia, labyrinthine disorders, or cerebral hemorrhages. Average age of onset of cerebrovascular manifestations is 33.8 years. Personality change and psychotic behavior can manifest with increasing age.
The current approved treatment for Fabry disease is enzyme replacement therapy (“ERT”). Two α-Gal A products are currently available for the treatment of Fabry disease: agalsidase alfa (Replagal®, Shire Human Genetic Therapies) and agalsidase beta (Fabrazyme®; Genzyme Corporation). These two forms of ERT are intended to compensate for a patient's inadequate α-Gal A activity with a recombinant form of the enzyme, administered intravenously. While ERT is effective in many settings, the treatment also has limitations. ERT has not been demonstrated to decrease the risk of stroke, cardiac muscle responds slowly, and GL-3 elimination from some of the cell types of the kidneys is limited. Some patients develop immune reactions to ERT.
1-deoxygalactonojirimycin and its salt, 1-deoxygalactonojirimycin hydrochloride (also known by its United States Adopted Name (USAN), migalastat hydrochloride) acts as a pharmacological chaperone for mutant α-Gal A by selectively binding to the enzyme, thereby increasing its stability and helping the enzyme fold into its correct three-dimensional shape. This stabilization of α-Gal A allows the cell's quality control mechanisms to recognize the enzyme as properly folded so that trafficking of the enzyme to the lysosome is increased, allowing it to carry out its intended biological function, the metabolism of GL-3. As a result of restoring the proper trafficking of α-Gal A from the ER to the lysosome, migalastat hydrochloride also reduces the accumulation of misfolded protein in the ER, which can alleviate stress on cells and some inflammatory-like responses that can be contributing factors in Fabry disease. Multiple in vitro and in vivo preclinical studies, as well as clinical studies, of migalastat hydrochloride have been conducted. Migalastat hydrochloride has been shown to increase the amount of intracellular α-Gal A protein and to enhance transport of mutant enzyme to the lysosome.