Autosomal dominant tubulointerstitial kidney disease (ADTKD) belongs to a group of renal hereditary disorders linked by common findings of tubulointerstitial disease and dominant inheritance. The renal clinical phenotype is characterized by chronic kidney disease, hyperuricemia, gout, and, inconstantly, renal cysts. Uromodulin (UMOD) gene mutations are related to the clinical phenotype of ADTKD-UMOD. We describe here a novel heterozygous mutation of UMOD (c.249C>G; p.Cys83Trp) in an affected 9-year-old boy with progressive renal impairment and hyperuricemia. His mother is also affected and received renal transplantation at the age of 31 years. We assume that this variant is likely to be the causative mutation in this family as it segregates with the disease, it is not present in the genomic databases, and it is predicted to be damaging by the principal software tools. Considering the progressive renal impairment of our proband at an early age (serum creatinine elevation at the age of 6, hyperuricemia at the age of 9) and the early age at end-stage renal disease of his mother, we hypothesize that this variant is associated with a severe clinical phenotype.