A Rare Case of a Child with X-linked Opitz G/BBB Syndrome Caused by a Novel Partial Microduplication in the MID1 gene: Implications for Genetic Diagnosis.

<p><strong>Background: </strong>Opitz G/BBB syndrome (XLOS) is a rare X-linked recessive disorder caused by mutations in <em>MID1</em> gene, characterized by midline congenital anomalies. Here we report a novel <em>MID1</em> duplication associated with unique phenotypic features.</p> <p><strong>Case Presentation: </strong>A 2-year-old Saudi male had prenatally oligohydramnios and was born with rectovesical fistula, hypospadias, anorectal malformation, and congenital heart defects (ASD/PDA). Family history revealed an X-linked inheritance pattern (multiple affected maternal male relatives).  He also exhibited developmental delay and growth parameters below the 3rd percentile</p> <p><strong>Conclusion: </strong>This is the first report of a <em>MID1</em> duplication involving exons 1–3, associated with rectovesical fistula and oligohydramnios, broadening the phenotypic spectrum of XLOS. We recommend that <em>MID1</em> testing be considered in males with atypical midline defects (including urogenital anomalies) and prenatal testing should be offered for at-risk pregnancies.</p>