The clinical significance of asymptomatic low molecular weight proteinuria detected on routine screening of children in Japan: a survey of 53 patients.

A nationwide questionnaire survey uncovered 53 patients with asymptomatic low molecular weight (LMW) proteinuria, 52 males and one female, aged 3 to 32 years. There was a slight tendency toward shortening stature with increasing age. Mild proteinuria was present in all of them, and microscopic hematuria was occasionally noted in one-fourth, while glucosuria or aminoaciduria was rare. The share of their urinary LMW proteins was increased as evidenced by an increase in the alpha-globulin fraction on cellulose-acetate membrane electrophoresis (27 patients) and/or by an increase in the LMW proteins on sodium dodecylsulfate-polyacrylamide gel electrophoresis (17 patients). Urinary beta 2-microglobulin, one of the LMW proteins, was measured and proved to be increased but electrophoretic analyses were not performed in 25 patients. Urinary N-acetyl-beta-D-glucosaminidase activity, an indicator of renal proximal tubular damage, was elevated in 31 of 38 patients studied: Histological studies of renal biopsies revealed focal changes: focal global sclerosis in seven and tubular atrophy and/or tubular casts in nine out of 32 patients studied.