Optical Genome Mapping (<scp>OGM</scp>) Identifies Multiple Structural Variants in a Case With Atypical Phelan‐<scp>McDermid</scp> Syndrome

Here we describe a neonate exhibiting hypotonia, macrocephaly, renal cysts, and respiratory failure requiring tracheostomy and ventilator support. Genetic analysis via rapid genome sequencing (rGS) identified a loss on chromosome 4 encompassing polycystin-2 (PKD2) and a loss on chromosome 22 encompassing SH3 and Multiple Ankyrin Repeat Domains 3 (SHANK3), indicative of Phelan-McDermid syndrome. Further analysis via traditional karyotyping, Optical Genome Mapping (OGM), and PacBio long-read sequencing revealed a more complex landscape of chromosomal rearrangements in this individual, including a balanced 3;12 translocation, and an unbalanced 17;22 translocation. The proband's phenotypic presentation is thought to be the result of Phelan-McDermid syndrome and represents an expansion of the described phenotypes to include significant respiratory failure. This study underscores the challenges and importance of comprehensive genetic testing in elucidating complex presentations and highlights the need for complementary testing methods to overcome limitations in resolution.