triphalangeal thumb-polysyndactyly syndrome
Definition An autosomal dominant condition (OMIM:174500) characterised by a wide spectrum of pre- and post-axial malformations due to an altered SHH expression pattern during limb development.
Molecular pathology Defects in LMBR1, a gene with an SHH* regulatory element—ZRS that resides in LMBR1’s intron 5, cause both triphalangeal thumb-polysyndactyly syndrome and polydactyly—preaxial 2.
*SHH is the gene that encodes Sonic Hedgehog, a protein central to early embryonic patterning for the anterior-posterior limb axis, the ventral somites and ventral neural tube.
Synonyms Polydactyly of triphalangeal thumb, triphalangeal thumb, triphalangeal thumb with polysyndactyly