To date, BS can be further subdivided into 5 different subtypes according to their causative genes: BS I (SLC12A1), BS II (KCNJ1), BS III (CLCNKB), BS IV (BSND, CLCNKA and CLCNKB) and BS V(MAGED2) (Kleta and Bockenhauer, 2006; Walsh et al., 2018; Besouw et al., 2020). The gene discussed is BSND; the disease is Bloom syndrome.