An exception is a report of hyperactivity in C3ar1 knockout mice in which the knockouts were generated from heterozygous incrosses.29 This raises the possibility that some behavioural effects in C3ar1-deficient mice (anxiety-like behaviour and a memory deficit) may have resulted from altered intrauterine environments or care by C3ar1-deficient mothers. This evidence concerns the gene C3AR1 and Anxiety.