• pups die within 48 hours of birth

• pups are of normal weight at birth and feed well initially

• pups typically stop feeding within 48 hours of birth

• pups are less active at the time they stop feeding

• no observable difference in plasma nitrite concentration

• no significant difference in the concentration of cGMP in the urine of mutant mice (J:101658)

• elevated serum levels of argininosuccinic acid, citrulline, and glutamine

• low serum levels of arginine

• arginine is a precursor in the synthesis of creatine via guanidinoacetate; no concentration differences are apparent in pooled skeletal muscle, heart and liver samples of these three compounds

• statistically significant increase in plasma ammonia levels

• reduced levels of arginase activity relative to control liver