It’s surprisingly common for babies to be born missing one or both kidneys; an estimated one in one thousand babies are born with a single kidney. Called renal agenesis, this condition is fatal if both kidneys are missing, and having just one can also lead to serious health problems like hypertension and early renal failure. In the September issue of GENETICS, Brophy et al. show for the first time that renal agenesis in humans can be caused by disruptions in the retinoic acid receptor pathway. They used whole exome sequencing in two affected families to identify a causal mutation and applied innovative CRISPR mutagenesis in mice to confirm their findings.
Two unrelated families from Iowa and Denmark each had multiple cases of renal agenesis. For both families, the researchers identified potentially causal mutations by comparing the whole exome sequences of several affected and unaffected family members. The gene GREB1L carried harmful mutations in both families: a missense SNV in one and a deletion interrupting a splice site in the other. Further sequencing confirmed that all affected individuals carried the mutated gene copies.
GREB1L is a cofactor for retinoic acid receptors that until now has never been implicated in mammalian kidney development—let alone renal agenesis. To confirm its effect, the researchers obtained a zebrafish mutant for the corresponding gene. Fish homozygous for the mutation showed abnormal early kidney development and died before reaching maturity. Knockdown treatment that decreased GREB1L expression in genetically normal fish had similar results, suggesting that GREB1L was indeed the gene causing the kidney developmental problems.
The final confirmation came from CRISPR-mediated mutations which were generated in F0 mice, eliminating the need for performing genetic crosses. Brophy et al. replicated the GREB1L mutation found in the Iowa family and generated mice with a variety of kidney development phenotypes spanning the range observed in the family. This suggests that there is developmental flexibility in how much GREB1L expression is needed to make one or two healthy kidneys. Furthermore, the use of CRISPR to generate mice that mirrored human phenotypes demonstrate how this technology can be used to quickly model idiosyncratic human mutations to better understand the causes of conditions like renal agenesis.
A Gene Implicated in Activation of Retinoic Acid Receptor Targets Is a Novel Renal Agenesis Gene in Humans
Patrick D. Brophy, Maria Rasmussen, Mrutyunjaya Parida, Greg Bonde, Benjamin W. Darbro, Xiaojing Hong, Jason C. Clarke, Kevin A. Peterson, James Denegre, Michael Schneider, Caroline R. Sussman, Lone Sunde, Dorte L. Lildballe, Jens Michael Hertz, Robert A. Cornell, Stephen A. Murray and J. Robert Manak
GENETICS September 1, 2017 207: 1 215-228; https://doi.org/10.1534/genetics.117.1125