HOXD13 and brachydactyly type A4: Mutations in the homeobox containing gene (HOXD13) can give rise to limb malformations with variable expressivity and a wide spectrum of clinical manifestations including synpolydactyly and brachydactyies types D and E. Zhao et al. [26] found a link between HOXD13 and two additional limb phenotypes – syndactyly type V and brachydactyly type A4, and suggested the term "HOXD13 limb morphopathies" for the spectrum of limb disorders caused by HOXD13 mutations.