Using capillary electrophoresis mass spectrometry, urinary proteome analysis of pediatric patients with Fanconi syndrome showed a reduced number of fragments derived from osteopontin and uromodulin, indicating loss of function of tubular excretion due to a disturbance of the endoplasmic reticulum in all patients with Fanconi syndrome, regardless of the underlying cause. Here, SPP1 is linked to Fanconi renotubular syndrome.