Autosomal dominant syndactyly type IV (SD4) is a rare form of syndactyly, caused by heterozygous mutations in a sonic hedgehog (<i>SHH</i>) regulatory element (<i>ZRS</i>) which resides in intron 5 of the <i>LMBR1</i> gene on chromosome 7q36.3. The gene discussed is LMBR1; the disease is syndactyly type 4.