Family-based linkage studies have identified a series of genes responsible for hereditary PC such as HPC1 (Carter et al., 1992; Cooney et al., 1997; Berry et al., 2000a), PCAP (Neuhausen et al., 1999; Berry et al., 2000a; Xu et al., 2001), HPCX (Schleutker et al., 2000), CAPB (Berry et al., 2000a; Xu et al., 2001), HPC20 (Berry et al., 2000b), HOXB13 (Breyer et al., 2012; Xu et al., 2013) etc. Over the last decades, Genome wide associated studies (GWAS) have identified about 160 common risk loci in PC, suggesting a polygenic model of PC (Farashi et al., 2019). Here, CSAD is linked to pachyonychia congenita.