Evaluation of the ISL1 gene in the pathogenesis of bladder exstrophy in a Swedish cohort

Bladder exstrophy is a congenital closure defect of the urinary bladder with a profound effect on morbidity. Although the malformation is usually sporadic, a genetic background is supported by an increased recurrence risk in relatives, higher concordance rates in monozygotic twins and several associated chromosomal aberrations. Recently, the ISL1 gene was presented as a candidate gene for bladder exstrophy and epispadias complex (BEEC) development in two different studies. In our study, we screened for genetic variants in the ISL1 gene in DNA from 125 Swedish patients using Sanger sequencing and array-CGH analysis. In addition, we evaluated ISL1 expression in RNA of human bladder during embryonic and fetal weeks 5–10 relative to that in lung tissue (week 9). In total, 21 single-nucleotide variants were identified, including a potentially novel missense variant, c.137C>G p.(Ala46Gly), substituting a conserved amino acid. This variant was inherited from an unaffected mother. No structural variants were identified. RNA sequencing revealed ISL1 mRNA expression during the critical time frame of human bladder development. In conclusion, we did not detect any known or likely pathogenic variants in the ISL1 gene in 125 Swedish BEEC patients, indicating that variation in the ISL1 gene is not a common genetic mechanism of BEEC development in the Swedish population. Bladder defect: Swedish patients lack putative disease-causing mutation A gene previously linked to birth defects of the bladder does not seem to cause the abnormality in affected patients from Sweden. A research group led by Agneta Nordenskjöld from the Karolinska Institutet in Stockholm screened 125 Swedish patients with bladder exstrophy for variants in the ISL1 gene. Recent studies showed association to a SNP near this gene conferring susceptibility to this rare bladder defect, with a protruding bladder outside the belly in new-borns. Nordenskjöld’s team found no disease-causing variants in this gene in their patients. The researchers also measured ISL1 activity in embryonic and fetal bladders, and saw expression levels spike at around eight weeks of gestation. This suggests that ISL1 is important for normal bladder development, even if mutations in the gene rarely explain cases of bladder exstrophy in Sweden.