However, IHH expression was observed in the autopod of limb buds, suggesting that osteosclerosis in the Cp mutant is mainly caused by the loss of IHH. We found typical TUNEL-positive cells, which result from the accumulation of unrepaired DSBs, in the head mesenchyme, neural tube, and its surrounding tissues in the Cp/Cp embryos, but not in the heart tissue. The gene discussed is IHH; the disease is osteosclerosis.