TMEM16E/ANO5 mutations related to bone dysplasia or muscular dystrophy cause opposite effects on lipid scrambling

Mutations in the human TMEM16E/ANO5 gene are causative for gnathodiaphyseal dysplasia (GDD), a rare bone malformation and fragility disorder, and for two types of muscular dystrophy (MD). Previous studies have demonstrated that TMEM16E/ANO5 is a Ca²⁺‐activated phospholipid scramblase and that the mutation c.1538C>T (p.Thr513Ile) causing GDD leads to a gain‐of‐function phenotype. Here, using established HEK293‐based functional assays, we investigated the effects of MD‐related and further GDD‐related amino acid exchanges on TMEM16E/ANO5 function in the same expression system. These experiments also revealed that the gradual changes in HEK293 cell morphology observed upon expression of TMEM16E/ANO5^GDD mutants are a consequence of aberrant protein activity. Our results collectively demonstrate that, on the level of protein function, MD mutations are associated to loss‐of‐function and GDD mutations to gain‐of‐function phenotypes, confirming conjectures made on the basis of inheritance modes.