Prenatal Diagnosis of Non‐Syndromic Congenital Sodium Diarrhea by Serial Ultrasonography and Whole‐Exome Sequencing: A Case Report and Brief Review

Congenital sodium diarrhea (CSD) is a rare inherited enteropathy. We report a case of non-syndromic CSD (non-sCSD) diagnosed prenatally. Serial ultrasounds from 22 weeks and 5 days to 28 weeks and 6 days revealed progressive rectal dilation (0.80-1.86 cm), rectal hyperperistalsis, evolving small bowel dilation with a "honeycomb" pattern and polyhydramnios. Projectile meconium expulsion at 28 weeks and 6 days confirmed intrauterine diarrhea. Whole-exome sequencing (WES) on amniotic fluid identified compound heterozygous pathogenic variants in the SLC9A3 gene, confirming the diagnosis. To our knowledge, this is the first antenatally diagnosed and genetically confirmed case of SLC9A3-related non-sCSD. This case demonstrates that the integration of serial prenatal ultrasonography, specifically tracking progressive rectal dilation and hyperperistalsis, with WES may enable the early antenatal diagnosis of SLC9A3-related non-sCSD. This approach provides critical information for prognosis, perinatal management, and family genetic counseling.