Investigation of Chromatin Modifiers to Elucidate the Phenotypic Variability of Congenital Heart Disease in Patients with 22q11.2 Deletion Syndrome

PROJECT SUMMARY/ABSTRACT: Congenital heart disease (CHD) presents a worldwide health burden as the most common type of congenital abnormality, affecting ~1% of live births. While it remains the leading contributor to birth defect mortality, the causes of CHD remain to be uncovered. Development of the heart is itself a complex process that is controlled and regulated by multiple cell types, largely arising from the pharyngeal apparatus, a transient structure in embryogenesis. The conotruncal region of the heart, composed of the outflow tract and great vessels, is particularly susceptible to congenital anomalies since its formation and remodeling involve extensive developmental processes. Conotruncal defects (CTDs) represent about 30% of all CHDs and occur in 40% of patients with 22q11.2 deletion syndrome (22q11.2DS). TBX1, encoding a T-box transcription factor, is the main causative gene for CTDs in 22q11.2DS, yet haploinsufficiency is not sufficient to explain the variable expressivity of these defects. Therefore, 22q11.2DS represents a unique population in which to uncover genetic modifiers of CTDs. To identify potentially damaging rare coding variants as modifiers, our lab performed whole genome sequence analysis on 1,182 subjects with 22q11.2DS, with and without CHD. We found that chromatin regulatory genes occurred in 8.5% of the 22q11.2DS subjects with CTDs. Some of these genes are also associated with sporadic CHD in the general population, which is strongly suggestive that precise regulation of chromatin, and consequently transcription, is essential for proper cardiac development. Our study aims to investigate the interaction of chromatin regulatory genes, specifically Kmt2c and Kmt2d, with Tbx1 in mouse models. KMT2C and KMT2D encode histone methyltransferases of the COMPASS family and they have also been implicated as causative for sporadic CHD. I therefore hypothesize that Tbx1 and Kmt2c/d genetically interact in the developmental processes critical for proper formation of the conotruncal region of the heart. To test this interaction, I have generated mouse crosses for the conditional knockout of Kmt2c, Kmt2d, and Kmt2c/d in the Tbx1 lineage. I will characterize cardiac defects through molecular and cellular approaches, as well as through functional genomics studies that will delineate the shared and unique developmental roles of Kmt2c/d and Tbx1. This will further the understanding of the genetic architecture of heart development and, consequently, the etiology of CHD, knowledge of which will improve diagnosis and treatment.