MUC1 and Chronic tubulointerstitial nephritis: Secondly, alleles with longer VNTR (>55 repeats) in exon 2 of MUC1 have been linked to increased levels of serum urea und serum urate as biomarkers for reduced kidney function and with the risk for chronic tubulointerstitial nephritis as opposed to shorter VNTRs (Mukamel et al, 2021).