ATM and obesity due to melanocortin 4 receptor deficiency: To understand the role of this obesity-associated ATM accumulation, pioneering studies using osteopetrotic Csf-1op/op mice carrying a homozygous missense mutation in the Csf-1 gene (Weisberg et al., 2003; Wiktor-Jedrzejczak et al., 1990; Yoshida et al., 1990) and BM chimeras suggested that such obesity-associated ATMs were of monocytic origin (Weisberg et al., 2003).