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Gene therapy is the delivery of a therapeutic gene for endogenous cellular expression with the goal of rescuing a disease phenotype. It has been used to treat an increasing number of human diseases with many strategies proving safe and efficacious in clinical trials. Gene delivery may be viral or non-viral, performed in vivo or ex vivo , and relies on gene integration or transient expression; all of these techniques have been applied to the treatment of Fabry disease. Fabry disease is a genetic disorder of the α-galactosidase A gene, GLA , that causes an accumulation of glycosphingolipids in cells leading to cardiac, renal and cerebrovascular damage and eventually death. Currently, there are no curative treatments available, and the therapies that are used have significant drawbacks. These treatment concerns have led to the advent of gene therapies for Fabry disease. The first Fabry patients to receive gene therapy were treated with recombinant lentivirus targeting their hematopoietic stem/progenitor cells. Adeno-associated virus treatments have also begun. Alternatively, the field of gene-editing is a new and rapidly growing field. Gene-editing has been used to repair disease-causing mutations or insert genes into cellular DNA. These techniques have the potential to be applied to the treatment of Fabry disease provided the concerns of gene-editing technology, such as safety and efficiency, were addressed. This review focuses on the current state of gene therapy as it is being developed for Fabry disease, including progresses and challenges as well as an overview of gene-editing and how it may be applied to correct Fabry disease-causing mutations in the future. [ABSTRACT FROM AUTHOR]

Background and objectives Screening for Fabry disease (FD), an X-linked lysosomal storage disorder, reveals a significant number of individuals with a genetic variant of unknown significance without classical FD manifestations; these variants in the α-galactosidase A gene often result in a high residual leukocyte α-galactosidase A and it is unclear whether these individuals suffer from FD. Therefore, a structured diagnostic approach is warranted. We present a diagnostic algorithm on how to approach adults with chronic kidney disease and an uncertain diagnosis of FD nephropathy. Design, setting, participants, and measurements A modified Delphi procedure was conducted to reach consensus among 11 FD experts. A systematic review was performed to identify possible criteria that could confirm or exclude FD nephropathy. Results The gold standard for FD nephropathy was defined as characteristic storage on electron microscopy (EM) in a kidney biopsy in the absence of medication that may induce similar storage. The suggested criteria to confirm FD nephropathy are as follows: ‘renal cysts’, ‘Maltese cross sign’, ‘immunohistochemical staining of Gb3 in urine’ and ‘high urinary Gb3’; and to exclude FD nephropathy: ‘absence of renal cysts’, ‘small kidneys’ and ‘high protein excretion’ were rejected because of low or uncertain specificity. Urinary Gb3 may be increased in other kidney diseases and there was no agreement on this criterion, although a third of the panel indicated that it is sufficient to diagnose FD nephropathy. The ‘Maltese cross sign’ and ‘high urinary Gb3’ were selected as red flags to suggest the possibility of FD nephropathy, but are not sufficient for a definite diagnosis of FD nephropathy. Conclusions In adults with chronic kidney disease, an α-galactosidase A gene variant and an uncertain diagnosis of FD, a kidney biopsy with EM analysis should be performed to confirm or reject the diagnosis of FD nephropathy. Other criteria currently cannot substitute for a biopsy in these cases. [ABSTRACT FROM AUTHOR]

Abstract: Fabry disease is a complex, multisystemic and clinically heterogeneous disease, in which the urinary excretion of globotriaosylceramide (Gb3), the principal substrate of the deficient enzyme, α-galactosidase A, is more prominent than the increased concentrations of the lipid in the plasma of affected hemizygotes and heterozygotes. We have developed and validated a simultaneous analysis of Gb3 and creatinine in a 2.6-min run using filter paper discs saturated with urine and analyzed by LC–MS/MS. Using this method, we studied the relationship between urinary levels of total Gb3/creatinine excretion and four types of mutations in the GLA gene (missense, nonsense, frameshift, and splice-site defects) in 32 children and 78 adult patients with Fabry disease. Forty-one patients were treated by enzyme replacement therapy and 69 were untreated. Our results show that the mean recoveries of Gb3 and creatinine from the urine filter paper standards were 91% and 97%, respectively, with precision, reproducibility, and linearity within acceptable ranges. Statistical analysis using the independent variables of sex, age, types of mutations and treatment showed that the mutation factor has a statistically significant impact on urinary Gb3 excretion (p =0.0007). This means that the levels of urinary excretion of Gb3/creatinine in children and adults with Fabry disease are directly related to the types of mutations. The same correlation was found for the sex (p <0.0001) and treatment (p =0.0011). In conclusion, we studied 35 mutations in 110 children and adults with Fabry disease and found a significant correlation between the types of mutations and total Gb3 excretion in Fabry patients. [Copyright &y& Elsevier]

Fabry disease is due to a deficiency in alpha-galactosidase A (a-gal A) activity. Enzyme therapy is used to treat Fabry disease although the cost is high and biweekly infusions are required long-term. We have shown that when a-gal A is overexpressed in cells, a portion of the hydrolase is secreted and can be taken up and used functionally by unmodified bystander cells. Based on this concept, and building on extensive preclinical data we generated previously, we have launched a multi-center, phase I clinical trial in Canada using gene transfer to treat men with Fabry disease of the classical phenotype (clinicaltrials.gov#NCT02800070) and to determine the feasibility and safety of this procedure. The protocol involves mobilization of Fabry patient hematopoietic stem/progenitor cells (HSPCs), ex vivo recombinant lentivirus-mediated gene transfer of a codon-optimized human a-gal A cDNA into those cells, and infusion of the transduced HSPCs into minimally ablated autologous recipients. The first Fabry patient received a single dose of vector-transduced cells in January 2017. Since then two other Fabry patients have also received the transduced cell product (with more patients in the queue). With regards to safety - no serious adverse events have occurred in any Fabry patient in our trial to date. We now report results for patient 1 at two years post-infusion of the transduced cells. We tracked a-gal A activity in leukocytes and plasma, vector copy number in peripheral blood and bone marrow cells, antibody titers in plasma, and changes to enzyme substrates and catabolites in both plasma and urine. Results show durable engraftment and persistence of vector-transduced HSPCs in this Fabry patient that are functionally enabled to produce a-gal A continually. This protocol appears to be feasible and safe however, application to other patients and long-term effectiveness are still to be studied [ABSTRACT FROM AUTHOR]