A C-to-A nonsense mutation changes codon 27 from serine (TCG) to an amber stop codon (TAG) (SW:Q6R3M4 p.S27*), and results in a truncated protein lacking any catalytic function. The allele was present in every 129 strain analyzed, including 129P3/J, 129X1/SvJ, 129P1/ReJ and 129P2/Ola. C57BL/6J and BALB/c mice did not contain the mutation. (J:85061, J:228234, J:273998)