Figure 2: The index case carries a missense mutation, c.650G>A in the SPG3A gene. SPG3A is localized on chromosome 14q11-q21 and encodes atlastin1, a 558 amino acid protein with a molecular mass of 63.5 kD containing three conserved motifs (P-loop, DxxG and RD) characteristic of guanylate binding/GTPase activity.