Interestingly, gene therapy based on rAAV administered to adult mice has proven to improve lifespan, weight gain and some biochemical parameters in several UCD mouse models, namely for deficiencies of OTC [24,25], ARG1 [24], CPS1 [27], NAGS [40], ASA [41,42] and CTLN1 [34,35]. The gene discussed is ARSA; the disease is urea cycle disorder.