Triphalangeal Thumb Polydactyly

Triphalangeal thumb (TPT) is the hallmark feature in individuals with mutations in the zone of polarizing activity regulatory sequence (ZRS), which is contained within intron 5 of the LMBR1 gene. Mutations in ZRS have been reported in individuals with PPD2 (TPT with or without preaxial polydactyly), TPT polysyndactyly, syndactyly IV (complete syndactyly with polydactyly), and Werner mesomelic syndrome (tibial hypoplasia, polysyndactyly, TPT).