A Study of Renal Function in Treatment-naïve, Young Male Patients With Fabry Disease

Inclusion Criteria: * The patient and/or their parent/legal guardian is willing and able to provide signed informed consent. If the patient is below the age of consent per local guidelines, he is willing to provide assent, if deemed able to do so. * The patient must have a confirmed diagnosis of Fabry disease as documented by leukocyte α-galactosidase A (αGAL) of \<4 nmol/hr/mg leukocyte (preferred assay; results from a central laboratory). If the leukocyte αGAL activity assay is difficult to obtain, the patient may be enrolled based on documented plasma αGAL \<1.5 nmol/hr/mL (results from a central laboratory), with the agreement of the Genzyme Medical Monitor. Exclusion Criteria: * Patient has received prior treatment with enzyme replacement therapy (ERT) or oral pharmacological chaperone therapy for Fabry disease. * Patient has received an investigational drug within 30 days of the screening visit. * Patient is receiving any of the following medications and is clinically unable or unwilling to temporarily discontinue treatment with these medications for the indicated washout period prior to the renal function assessments until completion of these assessments: * Angiotensin converting enzyme inhibitors or angiotensin receptor blockers (6 week washout); * Non-steroidal anti-inflammatory drugs (3 day washout). * NOTE: Patients who are on chronic dialysis or have had a kidney transplant will not be required to discontinue the above medications because renal function assessments will not be performed in these patients. * Patient has any contraindication mentioned in the labeling of iohexol. NOTE: patients with an eGFR \<30 mL/min/1.73m\^2 and patients who are on chronic dialysis or have had a kidney transplant may be enrolled irrespective of any contraindication to iohexol because iGFR will not be measured in these patients. * Patient has any medical condition or extenuating circumstance which, in the opinion of the Investigator, could interfere with the patient's ability to complete all study procedures, or with the interpretation of study results (e.g., diabetes mellitus). * The patient and/or their parent or legal guardian, in the opinion of the Investigator, is unable to adhere to the requirements of the study.