glomerulonephritis affecting a small proportion of renal glomeruli that commonly presents with hematuria and may be associated with acute upper respiratory infection in young males, not usually due to streptococci; associated with IgA deposits in the glomerular mesangium and may also be associated with systemic disease, as in Henoch-Schönlein purpura. SYN: Berger disease, Berger focal glomerulonephritis, focal nephritis, IgA nephropathy.