Agalsidase alfa and kidney dysfunction in Fabry disease

Baseline characteristics of patients enrolled in the Canadian Fabry Disease Initiative

The Canadian Fabry Disease Initiative [CFDI] is a longitudinal study evaluating all Canadians diagnosed with Fabry disease [FD]. The study has 3 cohorts: Cohort 1A which includes 81 subjects who were on enzyme replacement therapy [ERT] prior to October 2006, Cohort 1B which has ongoing enrolment of subjects newly started on ERT who are randomized to agalsidase alfa or agalsidase beta, and Cohort 1C where subjects who do not meet nationally accepted Canadian criteria for ERT are followed to assess the natural history of disease complications. The study currently enrols 244 patients [95 males and 149 females] with a mean age of 41.9+/-14.5years. There is a high prevalence of the c.427G>C mutation. Cohort 1A contains 82 patients [59 males, 23 females] of whom 42% are known to have cardiac complications of FD and 38% renal complications. Cohort 1B at the time of writing contained 37 patients [15 males, 22 females] of whom the indications for ERT were cardiac in 55% and renal in 60%. Cohort 1C at the time of writing contained 125 patients [22 males, 103 females]. Enrolment is ongoing in both Cohorts 1B and 1C. When compared to subjects in the Fabry Outcome Survey and the Fabry Registry, subjects in the CFDI are less likely to be male reflecting less ascertainment bias. The CFDI is a robust national data set that will contribute to available data on the natural history of FD and on the comparative efficacy of the two commercially available ERT products.

The value of estimated GFR in comparison to measured GFR for the assessment of renal function in adult patients with Fabry disease

BACKGROUND

Renal disease is one of the major complications in Fabry disease, an X-linked lysosomal storage disease due to deficiency of the enzyme alpha-galactosidase A. The aim of our study was to determine the value of creatinine-, cystatin C- and beta-trace-based formulas for the estimation of glomerular filtration rate (eGFR) in Fabry patients. For comparison, the gold standard method (125)I-labelled iothalamate/(131)I-labelled hippuran [measured GFR (mGFR)] was used.

METHODS

GFR was estimated by using 11 different formulas based on creatinine, cystatin C and beta-trace protein. Accuracy and precision, detection of early decline of renal function and follow-up of renal function by eGFR was compared to mGFR.

RESULTS

One hundred and thirty-six GFR measurements and plasma samples were available from 36 (20 male) Fabry patients, treated with agalsidase alpha or beta with a median follow-up of 3.1 (range 1.5-5.2) years. Median mGFR was 97.3 (15.5-148.6) ml/min/1.73 m(2) in males and 84.4 (23.0-131.0) ml/min/1.73 m(2) in females at the start of follow-up.

CONCLUSIONS

Although none of the investigated endogenous markers proved to be an equivalent substitute for mGFR in Fabry patients, the Stevens equation, a creatinine- and cystatin C-based formula, most closely approximated the mGFR. When a creatinine-based formula is preferred, considering that there is no standardized method available for cystatin C, the abbreviated Modification of Diet in Renal Disease (aMDRD) and the recently developed Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formulas had the best performance. In male Fabry patients, the aMDRD may overestimate GFR, especially in the higher ranges. In these cases, CKD-EPI may perform better.

Alpha-galactosidase A-Tat fusion enhances storage reduction in hearts and kidneys of Fabry mice

The protein transduction domain from human immunodeficiency virus (HIV) Tat allows proteins to penetrate the cell membrane. Enhanced cellular uptake of therapeutic proteins could benefit a number of disorders. This is especially true for lysosomal storage disorders (LSDs) where enzyme replacement therapy (ERT) and gene therapy have been developed. We developed a novel recombinant lentiviral vector (LV) that engineers expression of alpha-galactosidase A (alpha-gal A)-Tat fusion protein for correction of Fabry disease, the second-most prevalent LSD with manifestations in the brain, kidney and heart. In vitro experiments confirmed mannose-6-phosphate independent uptake of the fusion factor. Next, concentrated therapeutic LV was injected into neonatal Fabry mice. Analysis of tissues at 26 wks demonstrated similar alpha-gal A enzyme activities but enhanced globotriaosylceramide (Gb3) reduction in hearts and kidneys compared with the alpha-gal A LV control. This strategy might advance not only gene therapy for Fabry disease and other LSDs, but also ERT, especially for cardiac Fabry disease.

Assessment of renal pathology and dysfunction in children with Fabry disease

Overt renal disease often first presents in male individuals with Fabry disease in early to middle adulthood, but proteinuria and reduced GFR may occur in adolescents and in young children. More recently, kidney biopsy data have shown early renal histologic changes in pediatric patients, and kidney dysfunction, primarily proteinuria, seems to be more common in girls. Renal investigations and their timing in children remain poorly defined. A consensus on renal investigations is necessary to understand the natural progression of the disease and to evaluate the efficacy of treatments such as enzyme replacement therapies. This article addresses three main categories: Use of GFRs, measuring albuminuria, and renal biopsies in children.

Enzyme replacement therapy with agalsidase alfa in patients with Fabry's disease: an analysis of registry data

BACKGROUND

We analysed 5-year treatment with agalsidase alfa enzyme replacement therapy in patients with Fabry's disease who were enrolled in the Fabry Outcome Survey observational database (FOS).

METHODS

Baseline and 5-year data were available for up to 181 adults (126 men) in FOS. Serial data for cardiac mass and function, renal function, pain, and quality of life were assessed. Safety and sensitivity analyses were done in patients with baseline and at least one relevant follow-up measurement during the 5 years (n=555 and n=475, respectively).

FINDINGS

In patients with baseline cardiac hypertrophy, treatment resulted in a sustained reduction in left ventricular mass (LVM) index after 5 years (from 71.4 [SD 22.5] g/m(2.7) to 64.1 [18.7] g/m(2.7), p=0.0111) and a significant increase in midwall fractional shortening (MFS) from 14.3% (2.3) to 16.0% (3.8) after 3 years (p=0.02). In patients without baseline hypertrophy, LVM index and MFS remained stable. Mean yearly fall in estimated glomerular filtration rate versus baseline after 5 years of enzyme replacement therapy was -3.17 mL/min per 1.73 m(2) for men and -0.89 mL/min per 1.73 m(2) for women. Average pain, measured by Brief Pain Inventory score, improved significantly, from 3.7 (2.3) at baseline to 2.5 (2.4) after 5 years (p=0.0023). Quality of life, measured by deviation scores from normal EuroQol values, improved significantly, from -0.24 (0.3) at baseline to -0.17 (0.3) after 5 years (p=0.0483). Findings were confirmed by sensitivity analysis. No unexpected safety concerns were identified.

INTERPRETATION

By comparison with historical natural history data for patients with Fabry's disease who were not treated with enzyme replacement therapy, long-term treatment with agalsidase alfa leads to substantial and sustained clinical benefits.

FUNDING

Shire Human Genetic Therapies AB.

Enzyme replacement therapy and Fabry nephropathy

Involvement of the kidneys in Fabry disease ("nephropathy") occurs in male and female individuals. The majority of patients with progressive nephropathy will have significant proteinuria and develop progressive loss of kidney function, leading to ESRD. All too often, treating physicians may ignore "normal" serum creatinine levels or "minimal" proteinuria and fail to assess properly the severity of kidney involvement and institute appropriate management. Fabry nephropathy is treatable, even in patients with fairly advanced disease. Although the cornerstone of therapy remains enzyme replacement therapy with agalsidase, this treatment alone does not reduce urine protein excretion. Treatment with angiotensin receptor blockers or angiotensin-converting enzyme inhibitors must be added to enzyme replacement therapy to reduce urine protein excretion with the hope that this will stabilize kidney function. Kidney function, with at least estimated GFR based on serum creatinine and measurements of urinary protein, should be measured at every clinic visit, and the rate of change of the estimated GFR should be followed over time. Antiproteinuric therapy can be dosed to a prespecified urine protein target rather than a specific BP goal, with the proviso that successful therapy will usually lower the BP below the goal of 130/80 mmHg that is used for other forms of kidney disease. The overall goal for treating Fabry nephropathy is to reduce the rate of loss of GFR to -1 ml/min per 1.73 m(2)/yr, which is that seen in the normal adult population. A systematic approach is presented for reaching this goal in the individual patient.

The pharmacological chaperone 1-deoxygalactonojirimycin reduces tissue globotriaosylceramide levels in a mouse model of Fabry disease

Fabry disease is an X-linked lysosomal storage disorder caused by a deficiency in alpha-galactosidase A (alpha-Gal A) activity and subsequent accumulation of the substrate globotriaosylceramide (GL-3), which contributes to disease pathology. The pharmacological chaperone (PC) DGJ (1-deoxygalactonojirimycin) binds and stabilizes alpha-Gal A, increasing enzyme levels in cultured cells and in vivo. The ability of DGJ to reduce GL-3 in vivo was investigated using transgenic (Tg) mice that express a mutant form of human alpha-Gal A (R301Q) on a knockout background (Tg/KO), which leads to GL-3 accumulation in disease-relevant tissues. Four-week daily oral administration of DGJ to Tg/KO mice resulted in significant and dose-dependent increases in alpha-Gal A activity, with concomitant GL-3 reduction in skin, heart, kidney, brain, and plasma; 24-week administration resulted in even greater reductions. Compared to daily administration, less frequent DGJ administration, including repeated cycles of 4 days with DGJ followed by 3 days without or every other day with DGJ, resulted in even greater GL-3 reductions that were comparable to those obtained with Fabrazyme. Collectively, these data indicate that oral administration of DGJ increases mutant alpha-Gal A activity and reduces GL-3 in disease-relevant tissues in Tg/KO mice, and thus merits further evaluation as a treatment for Fabry disease.