The sequence variant c.953C>T in exon 7 changes serine in position 318 to leucine (p.Ser318Leu). Studies in transfected cells show that p.Leu318 is processed correctly, localized to the lysosomes and has retained some residual activity. p.Ser318 is located on the surface close to the disulphide bridge between p.Cys268 and p.Cys273.