PRODH and hyperprolinemia type 2: This increase in proline level in HPII may be caused by transcriptional changes in the proline metabolism pathway similar to what we see in our alh‐6 mutant worms (Figure 1h,i).The symptoms of HPI varies in severity depending on the degree of reduction in PRODH activity, and are characterized by neurological, auditory, and renal defects, while symptoms of HPII are variable and characterized by neurological defects (Geraghty et al., 1998).