Allelic variations at the haploid TBX1 locus do not influence the cardiac phenotype in cases of 22q11 microdeletion.

Microdeletion at the 22q11 locus is characterised by a high clinical variability. Congenital heart defects (CHD) are the most life-threatening manifestations of the syndrome and affect approximately 50% of patients carrying the deleted chromosome 22. The causes of this phenotype variability remain unknown although several hypotheses have been raised.