Autosomal dominant osteopetrosis type 2 (ADO2) is a rare disease known to affect the skeleton.1 First recognized by Albers-Schönberg2 and called Albers-Schönberg disease or marble bone disease,3 ADO2 is now documented to affect 1 in 20 000 live births.4,5 It has an autosomal dominant inheritance, with about 70% of patients carrying heterozygous missense mutations of the CLCN7 gene encoding the ClC7 2Cl−/1H+ antiporter.6–8 This antiporter is intrinsic to the acidic organelles, including lysosomes. The gene discussed is CLCN7; the disease is osteopetrosis.