Prenatal ultrasound detection of a DACT1 pathogenic variant overlapping Townes-Brocks Syndrome: A case report with asymptomatic maternal carrier

Townes-Brocks syndrome (TBS) is a rare autosomal dominant disorder typically caused by SALL1 mutations.Variants in DACT1 may produce overlapping phenotypes but are rarely described prenatally.We report a 32-year-old primigravida referred at 20th weeks for severe fetal growth restriction.Ultrasound revealed hyperechogenic bowel, abdominal calcifications, saddle-shaped nasal profile, cortical development anomalies, and triphalangeal thumbs.Amniocentesis with trio exome sequencing identified a heterozygous pathogenic DACT1 variant, also present in the asymptomatic mother.The pregnancy was terminated at 23 weeks due to poor prognosis.Postmortem confirmed imperforate anus and limb anomalies.This case highlights the value of detailed fetal imaging combined with advanced molecular testing for rare genetic syndromes, and the complexity of counseling in autosomal dominant disorders with incomplete penetrance.