TTC21B and Hepatic fibrosis: Homozygous NPHP1 possibly modified by heterozygous NPHP4 with early-onset ESKD [40];Compound heterozygous NPHP3 modified by heterozygous NPHP4 variant with early-onset ESKD and hepatic fibrosis [40,43];TTC21B contributes possible modifier alleles to NPHP4 [51].