In particular, type III BS is caused by loss-of-function mutations of the CLCNKB gene encoding for the human ClC-Kb chloride channel, whereas type IV BS is caused either by loss-of-function mutations in BSND gene encoding for the ClC-Ks accessory subunit barttin or by simultaneous mutations in CLCNKB and CLCNKA genes, this latter encoding for the human ClC-Ka isoform. The gene discussed is CLCNKA; the disease is Bloom syndrome.