PLEKHM1 and osteopetrosis: Inactive exocytosis (Fujiwara et al., 2016). Incisor absent (ia) rats, in which Plekhm1 is disrupted, exhibit age-dependent osteopetrosis and lack teeth. Their OCLs are nearly inactive and lack ruffled borders (Reinholt et al., 1999; McDonald et al., 2011).