Deletion of a remote enhancer near ATOH7 disrupts retinal neurogenesis, causing NCRNA disease

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Abstract
People with nonsyndromic congenital retinal nonattachment (NCRNA) are blind from birth. The authors show that NCRNA is caused by a deletion spanning a remote cis regulatory element upstream from ATOH7 (Math5), a transcription factor gene required for retinal development. The deleted region is a conserved secondary transcriptional enhancer of ATOH7. Individuals with nonsyndromic congenital retinal nonattachment (NCRNA) are totally blind from birth. The disease afflicts ∼1% of Kurdish people living in a group of neighboring villages in North Khorasan, Iran. We found that NCRNA is caused by a 6,523-bp deletion that spans a remote cis regulatory element 20 kb upstream from ATOH7 (Math5), a bHLH transcription factor gene that is required for retinal ganglion cell (RGC) and optic nerve development. In humans, the absence of RGCs stimulates massive neovascular growth of fetal blood vessels in the vitreous and early retinal detachment. The remote ATOH7 element appears to act as a secondary or 'shadow' transcriptional enhancer. It has minimal sequence similarity to the primary enhancer, which is close to the ATOH7 promoter, but drives transgene expression with an identical spatiotemporal pattern in the mouse retina. The human transgene also functions appropriately in zebrafish, reflecting deep evolutionary conservation. These dual enhancers may reinforce ATOH7 expression during early critical stages of eye development when retinal neurogenesis is initiated.