Duplication of HEY2 in cardiac and neurologic development.

HEY2 is a basic helix-loop-helix (bHLH) transcription factor that plays an important role in the developing mammalian heart and brain. In humans, nonsynonymous mutations in HEY2 have been described in patients with atrial ventricular septal defects, and a subset of individuals with chromosomal deletions involving HEY2 have cardiac defects and cognitive impairment. Less is known about the potential effects of HEY2 overexpression. Here, we describe a female child with tetralogy of Fallot who developed severe right ventricular outflow tract obstruction due to a combination of infundibular and valvular pulmonary stenosis. She was also noted to have hypotonia, lower extremity weakness, fine motor delay and speech delay. A copy number variation (CNV) detection analysis followed by real-time quantitative PCR analysis revealed a single gene duplication of HEY2. This is the only duplication involving HEY2 identified in our database of over 70,000 individuals referred for CNV analysis. In the developing heart, overexpression of HEY2 is predicted to cause decreased expression of the cardiac transcription factor GATA4 which, in turn, has been shown to cause tetralogy of Fallot. In mice, misexpression of Hey2 in the developing brain leads to inhibition of neurogenesis and promotion of gliogenesis. Hence, duplication of HEY2 may be a contributing factor to both the congenital heart defects and the neurodevelopmental problems evident in our patient. These results suggest that individuals with HEY2 duplications should be screened for congenital heart defects and monitored closely for evidence of developmental delay and/or cognitive impairment.