CA2 and osteopetrosis: Extremely rare forms of osteoclast-rich osteopetrosis are caused by defects in the carbonic anhydrase 2 (CA2) (Sly et al., 1983), pleckstrin homology and RUN domain-containing M1 (PLEKHM1) (Van Wesenbeeck et al., 2007), leucine-rich repeat kinase 1 (LRRK1) and melanocyte-inducing transcription factor (MITF) genes (Howaldt et al., 2020; Iida et al., 2016; Lu et al., 2014).