Microdeletions/duplications involving TBX1 gene in fetuses with conotruncal heart defects which are negative for 22q11.2 deletion on fluorescence in-situ hybridization

Objectives: Conotruncal heart defects (CTD) are associated with del22q11.2 syndrome, which is often diagnosed by fluorescence in-situ hybridization (FISH). However, in those negative for del22q11.2 on FISH, the etiology is usually obscure. We aimed to use high-resolution array comparative genomic hybridization (array CGH) to clarify the underlying genetic causes in these cases.

Methods: In this retrospective study, fetal samples of amniocytes or fibroblasts, taken either for prenatal diagnosis by amniocentesis or for postnatal survey after termination of pregnancy, were obtained from 45 fetuses with CTD and were investigated by cytogenetic analysis including karyotyping and FISH for del22q11.2 syndrome. Eight fetuses with no findings on karyotyping and FISH were investigated further by array CGH, real-time quantitative polymerase chain reaction (qPCR) and Sanger sequencing of TBX1.

Results: Array CGH revealed that three of the eight fetuses carried submicroscopic genomic imbalances. Of these, two cases showed similar small microdeletions/duplications in 22q11.2 (one 0.85 kb microdeletion and one 8.51 kb microduplication). The minimal shared region spanned exon 2 of TBX1, a candidate gene responsible for cardiovascular defects in del22q11.2 syndrome. In all eight cases, the array CGH results were confirmed by qPCR, and Sanger sequencing did not detect other molecular pathologies.

Conclusion: Our findings indicate an association between TBX1 variations and fetal CTD. The results also demonstrate the power of array CGH to further scrutinize the critical gene(s) of del22q11.2 syndrome responsible for heart defects. Array CGH apparently has diagnostic sensitivity superior to that of FISH in fetuses with CTD associated with del22q11.2 (and dup22q11.2) syndrome.