Extremely rare osteosclerotic disorders also include Caffey disease, Lenz-Majewski hyperostotic dwarfism, trichothiodystrophy-1 with axial osteosclerosis, and melorheostosis which are caused by mutations in COL1A1, PTDSS1, ERCC2, and MAP2K1, respectively [4–6]. Here, ERCC2 is linked to osteomesopyknosis.