For Morquio syndrome type B, the common human missense mutation W273L (position 274 in mice) was introduced into the Glb1 gene (Glb1<sup>W274L</sup>), while for GM1-gangliosidosis, a 20 bp mutation was generated to remove the catalytic nucleophile of β-gal (β-gal<sup>-/-</sup>).
While most MBD patients carry a common allele, c.817TG>CT (p.W273L), only few of the >100 mutations known in GM1 can be related to a certain phenotype.
A single French patient had a novel missense point mutation (Q408P) together with a known mutation (T500A) while the mentally retarded patients were both heterozygous for two mutations known in chronic GM1 gangliosidosis together with two novel missense point mutations (Y270D and H281Y) in the vicinity of W273L.