By comparing littermate Wlsfl/+;Gfap-Cre (phenotypically WT control) and Wlsfl/-;Gfap-Cre (mutant) mice, we observe that eliminating Wls in a subset of neural progenitors with Gfap-Cre has no effect on viability but is associated with (i) a ~ 25% reduction in body size and weight at early post-weaning ages that decreases to a ~ 5% reduction by six weeks of age and (ii) male infertility. The gene discussed is GFAP; the disease is male infertility.