Table 1.

PNPO mutations affecting enzyme structure and function.

Category	Variants	Mutations affecting
I	R95C, R116Q, R141C, R161C, R225 C/L/H and R229W/Q	catalytic site and ligand binding
II	E50K, P231S, G118Q/R	fold and protein stability
III	Residue deletion (S93S_A94Ldel), pre-mature stop codons (A174X), Loss of stop codons (X262Q) Frame shifts combine with loss of (L83W_fs*17, P150R_fs*27)	Ligand binding and protein fold
IV	D33V	Neither ligand binding nor fold