Nephritis (kidney inflammation) is most often caused by autoimmune diseases that affect major organs, although it can also result from infection. Nephritis can cause excessive amounts of protein to be excreted in urine, and fluid to build up in the body.
hope this helps...prevention of childhood diseases and outbreaks, higher school attendance rates and lower occurances of diseases for families that may heave come in contact with children.
Likely the chronological age, mainly because it would explain the differences in puberty stages between the two boys, which is an example of physical maturation.
