Our patient's clinical and biochemical features clearly oriented towards renal failure of tubular origin (metabolic acidosis, increased alpha-1 and beta-2 microglobulin levels, microalbuminuria, glycosuria and low urine osmolality), without any sign of significant glomerular involvement (normal serum immunoglobulins and complement and nonnephrotic proteinuria). The gene discussed is B2M; the disease is kidney failure.