Microduplication of 7q36.3 encompassing the SHH long-range regulator (ZRS) in a patient with triphalangeal thumb-polysyndactyly syndrome and congenital heart disease

Triphalangeal thumb-polysyndactyly syndrome (TPT-PS) is an autosomal dominant disorder with complete penetrance and a variable expression consisting of opposable triphalangeal thumbs, duplication of the distal thumb phalanx, pre-axial polydactyly and duplication of the big toes (hallux). The causative gene of TPT-PS has been mapped to 7q36.3. Sonic hedgehog (SHH) expressed in the zone of polarizing activity (ZPA) has an important role in defining the anterior-posterior axis and numbers of digits in limb bud development. Point mutation or duplication in the ZPA regulatory sequence (ZRS), a cis-regulator of SHH, will lead to TPT-PS. The present study describes a 1-year-old female congenital heart disease (CHD) patient with TPT-PS phenotype. In this Han Chinese family with TPT-PS, high resolution single nucleotide polymorphism array technology identified a novel 0.29 Mb duplication comprising ZRS at 7q36.3 where LMBR1 is located. Additionally, a novel deletion of 22q11.21 was detected in the proband with Tetralogy of Fallot. However, the parents and other relatives of the patient did not harbor this genomic lesion nor CHD. The findings supported the hypothesis that an increased copy number variation of ZRS is the genetic mechanism underlying the phenotype of TPT-PS, and corroborated that 22q11.21 deletion is a genetic cause of CHD.