A Novel ANO1 Gene Variant is Associated with Intestinal Dysmotility Syndrome Masquerading as Hirschsprung Disease: A Case Report

**Background:** Peristalsis is essential for gastrointestinal motility and is orchestrated by interstitial cells of Cajal (ICC), which generate slow waves via calcium-activated chloride channels. Anoctamin 1 (ANO1, also known as TMEM16A) is a calcium-activated chloride channel highly expressed in ICC and is critical for slow-wave generation. ANO1 dysfunction has been implicated in intestinal dysmotility syndromes, but only one prior report (Park et al., 2021) described a pathogenic ANO1 variant causing fatal neonatal disease in two brothers. This case report presents the third known case of ANO1-related intestinal dysmotility syndrome (OMIM: 620045).

**Methods:** This is a case report of a 2-month-old male infant, preterm (34 weeks gestation), delivered by cesarean section, with a history of neonatal intensive care unit admission for respiratory distress syndrome and delayed passage of meconium until day four of life. He presented with diarrhea, vomiting, and abdominal distension for 3 weeks. Vomitus was nonbloody, nonmucoidal, yellow, 1–2 times/day; diarrhea was loose, watery, yellow, 4–5 times/day. Clinical suspicion included galactosemia, cystic fibrosis, and Hirschsprung disease. Diagnostic workup included galactose-1-phosphate uridyltransferase assay, cystic fibrosis gene sequencing, Gastrografin barium enema, rectal biopsy with histopathological examination, and whole-exome sequencing (WES) with Sanger confirmation.

**Key Results:** Galactosemia and cystic fibrosis testing were negative. Barium enema showed a reversed rectosigmoid ratio with a smaller-caliber lower rectum compared to the sigmoid and colon, and multiple gas-filled loops suggesting distal intestinal obstruction, consistent with Hirschsprung disease. However, rectal biopsy histopathology demonstrated the presence of colonic ganglionic cells, ruling out Hirschsprung disease. WES identified a novel homozygous nonsense ANO1 pathogenic variant (c.1273G>T) resulting in a protein change p.Glu425Ter. The parents were consanguineous and heterozygous for the same variant, confirming autosomal recessive inheritance. The patient experienced multiple episodes of metabolic acidosis, dehydration, and electrolyte imbalances requiring pediatric intensive care unit admissions. He was managed conservatively and followed as an outpatient. Compared to the two previously reported cases, this patient had a milder phenotype: no dysmorphic features, normal weight gain, no cataracts, hypotonia, or developmental delay.

**Clinical Implications:** This case expands the known genotype-phenotype spectrum of ANO1-related intestinal dysmotility syndrome, demonstrating that a novel nonsense variant (c.1273G>T) can present with a milder clinical course than previously described. The condition should be considered in neonates with Hirschsprung disease-like features but normal rectal ganglia. Genetic testing (WES) is essential for diagnosis. The authors emphasize the need for functional studies to characterize this variant and establish genotype-phenotype correlations. This report also underscores the role of ANO1 in ICC function and gastrointestinal motility.