Exome Sequencing Identifies RET Associated Hirschsprung Disease in a Fetus with Echogenic Bowel

This is report of a case of RET associated Hirschsprung disease in a fetus diagnosed using exome sequencing. The fetus initially presented with echogenic bowel at 16 weeks with maternal first trimester serum screen showing increased risk for Trisomy 21. Amniotic fluid karyotype, Delta F508 CFTR genotype and maternal TORCH serology were normal. Subsequent ultrasonograms showed dilated bowel loops, predominantly large bowel. Following delivery at 24 weeks, a post-mortem examination was performed. Dilated bowel was confirmed with no structural gut abnormality and no other dysmorphic finding. Histopathology revealed agangliosis confirming a diagnosis of Hirschsprung disease. Exome sequencing done on fetal DNA from amniotic fluid revealed a putative pathogenic heterozygous c.1438G > A variant in exon 7 of RET gene, which was inherited from the asymptomatic mother. This enabled genetic counseling and prenatal diagnosis in subsequent pregnancy.