CTNS and cystinosis: Cystinosis is a rare autosomal recessive LSD, caused by mutations in the CTNS gene, encoding lysosomal membrane transporter Cystinosin (Kalatzis et al., 2001). Deletion of 57 kb of the CTNS gene is the most common mutation that accounts for approximately 75% of the affected alleles in northern Europe (Town et al., 1998; Attard et al., 1999).