P877: Distinct prenatal diagnostic pathways to uniparental disomy: Insights from two cases

Diagnostic Workup: Chorionic villus sampling was performed at 13w0d with normal routine testing (FISH, karyotype, and microarray).Expanded carrier screening revealed the couple to be heterozygotes for the likely pathogenic c.3317+1G>A variant in CIITA, associated with Bare Lymphocyte Syndrome, and fetal CIITA analysis on CVS demonstrated homozygosity for the likely pathogenic variant, consistent with a diagnosis of Bare Lymphocyte Syndrome.