Duodenal Duplication Cyst in Cardiofaciocutaneous Syndrome: A Possible Expansion of the Gastrointestinal Phenotype of RASopathies – A Case Report

Cardiofaciocutaneous (CFC) syndrome is a rare RASopathy caused predominantly by germline BRAF variants; functional gastrointestinal symptoms are common, but structural gastrointestinal malformations are exceptional. We report a 10-month-old male with a de novo BRAF (NM_004333.6):c.1914T>A, p.(Asp638Glu) pathogenic variant who presented neonatally with a duodenal duplication cyst causing partial pyloric obstruction, and underwent surgical excision at 3.5 months. To our knowledge, no previous duodenal duplication cyst has been reported in CFC syndrome or in any other RASopathy in the indexed literature. RAS/MAPK signalling regulates foregut recanalisation, raising the possibility of a mechanistic link, although causality cannot be established from a single observation. This hypothesis-generating case may expand the reported gastrointestinal phenotype of RASopathies; structural imaging may be considered in CFC patients with obstructive vomiting disproportionate to expected functional feeding difficulties.