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.

Background: Opitz G/BBB syndrome (XLOS) is a rare X-linked recessive disorder caused by mutations in MID1 gene, characterized by midline congenital anomalies. Here we report a novel MID1 duplication associated with unique phenotypic features. Case Presentation: 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 Conclusion: This is the first report of a MID1 duplication involving exons 1–3, associated with rectovesical fistula and oligohydramnios, broadening the phenotypic spectrum of XLOS. We recommend that MID1 testing be considered in males with atypical midline defects (including urogenital anomalies) and prenatal testing should be offered for at-risk pregnancies.