The p.Arg649Trp (c.1945C > T)
mutation affects a position that is involved in the interaction
with the phosphotyrosine residue of the substrate,
as shown by the proximity of this residue to the functional
group of a substrate-mimic molecule. The p.Asp643Aspfs*8
(c.1929_1933delTGGCA) mutation of patient 1 truncates
the protein right after the first alpha helix and before this
site of substrate recognition. As a result, this alpha helix
might fold properly but the resulting protein lacks the
position that interacts with the phosphotyrosine residue of
the substrate.