Identification and analysis of responsible gene for juvenile nephronophthisis complicated by retinitis pigmentosa

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In this study, we cloned a cDNA encoding the human homologue of TIN-ag and determined its nucleotide sequence. The deduced protein sequence of 476 amino acids included a signal peptide, six potential gycosylation sites, and an ATP/GTP-binding site, showing 85% homology with both rabbit and mouse TIN-ag. Human (h) TIN-ag contained a sequence showing similarity to that found in C. elegans and also resembling a cathepsin B-like cysteine protein Northern analysis indicated exclusive expression of this molecule in human kidney. Using a monoclonal antibody (H79) recognizing hTIN-ag, protein expression could be identified in cultured COS-1 cells transfected with hTIN-ag cDNA. The hTIN-ag gene was mapped by fluorescence in situ hybridization to chromosome 6p11.2-12.Recently we encountered a sibship with juvenile nephronophthisis complicated with retinitis pigmentosa. Immunofluorescence using H79 disclosed significantly reduced expression of TIN-ag on renal TBM in both patients. To determine the genetic alteration of TIN-ag in this family, hTIN-ag cDNA was produced and amplified using specific primers in a RT-PCR from RNA obtained from normal kidney and patients' kidneys. The cDNA was a 1.2-kb fragment representing the hTIN-ag coding region. Electrophoresis of the PCR product demonstrated hTIN-ag mRNA expression in normal human kidney but none in our patients' kidneys. These findings suggest involvement of TIN-ag defects in juvenile nephronophthisis.