Molecular characterization of tetralogy of Fallot within DiGeorge critical region of the chromosome 22

The purpose of this study was to determine whether the levels of heterozygosity and microdeletion of specific loci within the DiGeorge critical region (de122q11) are associated with different phenotypes of tetralogy of Fallot (TF). Examinations were conducted on 84 sporadic TF patients and their unaffected parents for de122q11, using the following 9 simple tandem repeat polymorphic microsatellite markers: D22S420, D22S427, D22S941, D22S944, D22S264, D22S311, D22S425, D22S303, D22S257. The microdeletions were confirmed using quantitative PCR with markers TUPLE 1, exon 2 of the UFD 1L gene, and D22S264; the boundaries of these microdeletions were estimated using genotypic analyses of the unaffected family members. The de122q11 was identified in 14 patients (16.6%). The boundary of the shortest region of deletion overlap (SRO) in these 14 TF patients was identified, proximally using D22S427 and distally using the TUPLE 1 gene. The deletion of exon 2 of the UFD 1L gene and TUPLE 1 gene was identified in 13 patients (13/14 cases; 93%). The SRO in TF patients with de122q11 was at or close to the ADU breakpoint and centromeric to the UFD1L gene. The level of heterozygosity for the marker D22S944 in TF patients without de122q11 (n = 70) was found to be significantly lower than expected. Overall, this study demonstrated the significantly low level of heterozygosity within DiGeorge critical region in TF patients with or without de122q11. Our results suggest that the genetic factors leading to DiGeorge/velocardiofacial syndrome might also be partly responsible for TF phenotypes.