Inclusion criteria
•    Age between 1 and 16 years (before 17th birthday) for Cohorts 1 and 2;
age between 6 months and 16 years (before 17th birthday) for Cohort 3
•    Estimated (based on SCr) Schwartz GFR between 30 and 90 ml/min|1.73m2 for Cohort 1 OR an estimated GFR between 45 and 90 ml/min|1.73m2 based on the updated Schwartz formula for Cohort 2
•    Willingness and ability to provide informed consent and assent
•    For Cohort 2, an equal distribution of children with glomerular and non-glomerular causes of disease were enrolled (i.e., 150 within each) and the study placed an upper limit of 60% for the percent of enrolled with non-glomerular disease. 

Exclusion Criteria
Among the children who fulfill the inclusion criteria, certain medical conditions and/or the inability to assess exposures of interest will deem them ineligible. Specifically, the following conditions comprise the exclusion criteria:  
•    Renal, other solid organ, bone marrow or stem cell transplantation
•    Dialysis treatment within the past three months
•    Cancer diagnosis or HIV diagnosis/treatment within last twelve months
•    Current pregnancy or pregnancy within past twelve months
•    Inability to complete major data collection procedures
•    Current enrollment in a randomized clinical trial in which the specific treatment is unknown
•    Not fluent in English or Spanish 
•    Plans to move out of area of any participating CKiD site (Families can be transferred to another CKiD site if they move) 
•    History of structural heart disease
•    Genetic syndromes involving the central nervous system (e.g., Downs syndrome)
•    History of severe to profound mental retardation (i.e., IQ<40, significant impairment in adaptive function and/or inability to independently execute self-care skills)
•    For cohort 3, children who are expected to receive kidney replacement therapy within 6 months of date of enrollment will not be recruited.