ESR1 and Osteopenia: (9) As summarized in Table 1, constitutive Ctsk‐Cre‐mediated ERα deletion in female, but not male, mice led to trabecular osteopenia and increased osteoclast numbers by 12 weeks of age, with no alterations in cortical bone.(8) The phenotype of the mice with LysM‐Cre‐mediated ERα deletion was slightly different, in that neither trabecular osteopenia nor increases in osteoclast numbers were evident at 12 weeks, but they were present by 22 weeks of age.(9)