A G-to-T transversion results in a nonsense mutation at glutamic acid codon 555 (ENSMUSP00000003620 p.E555*) in a conserved carboxy terminal region 135 bp upstream of the native stop codon. The presence of the mutation has been correlated with increased proline levels and is believed to be responsible for hyperprolinaemia observed in the Pro/Re strain. Full length transcript was identified by Northern blot analysis.