TCIRG1 and autosomal recessive osteopetrosis: Autosomal recessive osteopetrosis, which is usually a severe disorder, is caused by biallelic variants in genes affecting osteoclast development (eg, RANK, RANKL) or function (eg, TCIRG1, SNX10, CLCN7, OSTM1, CA2, PLEKHM1).(3) A condition originally described as type 1 autosomal dominant osteopetrosis (ADO) (now referred to as “high bone mass,” because it is not an osteopetrosis) occurs due to activating variants in LRP5 and causes the high‐bone‐mass phenotype, but is not associated with an increase in fractures.(4) Type 2 ADO is typically caused by monoallelic variants in the CLCN7 gene.(5)