The 22q11 deletion: DiGeorge and velocardiofacial syndromes and the role of TBX1

Investigation of TBX1 gene deletion in Iranian children with 22q11.2 deletion syndrome: correlation with conotruncal heart defects

BACKGROUND

DiGeorge syndrome (DGS) is the result of a microdeletion in chromosome 22q11.2 in over 90% of cases. DGS is the second most frequent syndrome after Down syndrome and has an incidence of 1/4000 births. Unequal crossover between low-copy repeats, on the proximal part of the long arm of chromosome 22, usually results in a 3 Mb deletion in one of the chromosome 22 and a reciprocal and similarly sized duplication on the other one. Several studies have indicated that TBX1 (T-box 1) haploinsufficiency is responsible for many of the phenotypic traits of 22q11.2 deletion syndrome. Conotruncal heart defects (CTDs) are present in 75-85% of patients with 22q11.2 deletion syndrome in Western countries.

METHODS

Among 78 patients fulfilling the criteria for DGS diagnosed by the fluorescence in situ hybridisation test, 24 had 22q11.2 deletion. Screening for TBX1 gene deletion was performed by multiplex ligation-dependent probe amplification (MLPA).

RESULTS

Our results revealed that of 24 patients with TBX1 gene deletion, 12 had CTDs while 12 did not show any heart defects.

CONCLUSIONS

Our findings indicate that other genes or gene interactions may play a role in penetrance or the severity of heart disease among patients with DGS.