Chromosome 21 open reading frame 91

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Chromosome 21 open reading frame 91, also known as C21orf91 or EURL (Expressed in Undifferentiated Retina and Lens), is a protein-coding gene on human chromosome 21 (location 21q21.1). It was first identified in chick embryos.

Biological role: The gene encodes a protein that appears to influence neural development, particularly in neural progenitor cells and neurons of the cerebral cortex. EURL is expressed in various tissues, including retina and lens, and its exact functions are still being studied.

Relevance to Down syndrome: Because C21orf91 sits on chromosome 21, changes in its gene dosage—such as an extra copy in Down syndrome—may affect brain development. Scientists are exploring how the amount of EURL protein impacts neural development and may contribute to neural differences seen in Down syndrome, using approaches that reduce or modify the gene’s expression to study its effects.

Note: The precise functions and interactions of this gene are not yet fully understood and are the subject of ongoing research.