Heterozygous mutations in the SGMS2 gene (p.Arg50*, p.Ile62Ser, p.Met64Arg) cause a rare skeletal disorder termed calvarial doughnut lesions with bone fragility (CDL) with or without spondylometaphyseal dysplasia, with low BMD, neonatal fractures, long-bone deformities, and short stature (OMIM #126550). The gene discussed is SGMS2; the disease is spondylometaphyseal dysplasia.