Abstract：Nephronophthisis (NPHP) is a group of autosomal recessive tubulointerstitial cystic kidney disorders. This article reports a case of NPHP type 12 caused by TTC21B mutations. The girl had an insidious onset, with moderate proteinuria, renal dysfunction, stage 2 hypertension, situs inversus, and short phalanges when she visited the hospital for the first time at the age of 3 years and 6 months. The renal lesions progressed to end-stage renal disease (ESRD) before she was 4 years old. Urine protein electrophoresis showed glomerular proteinuria. There were significant increases in urinary β2-microglobulin and α1-microglobulin. Gene detection revealed two compound heterozygous mutations, c.1552T > C (p.C518R) and c.752T > G (p.M251R), in the TTC21B gene, which came from her father and mother respectively. The c.752T > G mutation was a novel mutation. It is concluded that besides typical tubular changes of NPHP, marked glomerular damage is also observed in patients with TTC21B gene mutations.
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