CAST and Ataxia: Interestingly, the ataxia scores in F1 mice match those seen in C57BL/6Nlrp1b(129S1) transgenic mice, consistent with retention of one dominant LT-responsive allele of Nlrp1b, and further suggesting that both CAST/Ei and 129S1 alleles do in fact function in a similar, dominant manner to drive a less severe ERP.