he ADAM22 protein (Fig. 1C). Homozygous mutants showed no noticeable defects at birth and were indistinguishable from wild-type or heterozygous littermates during the first week. At postnatal day 10 (P10), most of the homozygous mutants were distinguishable by abnormalities such as reduced body weight and uncoordinated movements of their limbs. After P10, all homozygotes displayed severe ataxia (Fig.