No self-injurious behavior was found in HPRT-deficient mice treated with 9-ethyladenine.

It has been reported that 9-ethyladenine (9-EA) is an efficient inhibitor of APRT (adenine phosphoribosyltransferase) and that its administration causes self-injurious behavior (Lesch-Nyhan Syndrome-like symptoms) in HPRT (hypoxanthine-guanine phosphoribosyltransferase)-deficient mice. In contrast, we found neither any self-injurious behavior (SIB), such as visible injury or hair loss, nor any apparent decrease in APRT activity in HPRT-deficient mice treated with 9-EA. We also found that 9-EA has little irreversible or competitive inhibitory effect on APRT in vitro, even at a concentration of 10(-2) M. In light of the negative finding of SIB in APRT/HPRT double-deficient mice, it seems unlikely that SIB in HPRT-deficient mice is caused by lowered APRT activity. It is concluded that 9-EA is not a sufficient APRT inhibitor and cannot be used in experiments that mimic lowered APRT status in an animal model.