Podocyturia, a Non-Invasive Predictor of Renal Dysfunction in Fabry Nephropathy

Despite long-term recombinant enzyme replacement therapy, kidney failure remains a common and important complication of Fabry disease. Recent studies suggest that early administration of enzyme replacement therapy in sufficient dosage may prevent progression of kidney failure in patients with Fabry disease. Currently, there is no reliable non-invasive biomarker to detect early, occult kidney injury in these patients. Such early kidney injury detection is critical for guiding the decision as to when to initiate enzyme replacement therapy, and for identifying those patients with more severe kidney injury who may need higher doses of enzyme replacement therapy or additional forms of therapy.

Podocytes are special kidney cells with a crucial role in preventing escape of protein from the blood into the urine. Biopsy studies of Fabry disease patients suggest that podocyte injury occurs early and is progressive with increasing age in young Fabry disease patients. It is also likely that podocyte injury and loss leads to irreversible kidney lesions in later stages of Fabry disease nephropathy. Because injured podocytes are sloughed off into the urine (a manifestation known as podocyturia), quantification of urine podocytes might serve as a non-invasive and sensitive biomarker useful for predicting Fabry disease nephropathy risk; and to guide more effective Fabry disease treatment.

The investigators' preliminary data show correlations between presence of urinary podocytes and other markers of renal disease in adult Fabry disease patients; however, these cross-sectional data need to be expanded. The investigators have no information as to whether this potential biomarker could predict progression of the disease.

The investigators hypothesize that since podocyte injury plays a central role in kidney complications of Fabry disease, podocyte loss detected in the urine will identify patients with greater underlying kidney disease, and will identify patients with greater propensity for kidney disease progression. They also hypothesize that the number of podocytes in the urine of patients with Fabry disease will correlate directly with these patients' proteinuria, and will correlate inversely with their glomerular filtration rate (GFR) at baseline. Additionally the investigators hypothesize that the number of podocytes in the urine of patients with Fabry disease will predict increase in proteinuria and decline in glomerular filtration rate, as measured during long-term patient follow-up.

Data to be collected include identification of these patients' GLA gene mutation; measurement of their baseline a-galactosidase A enzyme activity; their baseline age, gender, height and weight; measurement of their baseline serum creatinine (SCr), eGFR, PCR and ACR; these patients' family history of Fabry disease, their history of kidney or systemic diseases, their medications including enzyme replacement therapy, and their medical information about other complications of Fabry disease (such as cardiomyopathy, arrhythmias, neuropathy and gastrointestinal problems).