P795: Detection of mosaic Prader-Willi syndrome in a buccal sample by CMA and WES

Case Presentation: A four-month-old female presented with webbed neck, short stature, microcephaly, failure to thrive, dysmorphic facial features, cardiac murmur, ventricular septal defect, abnormal transaminases, and hematochezia.No clinical suspicion of differences of sex development (DSD) was noted.CMA testing was requested.Diagnostic Workup: A 1.9 Mb pathogenic deletion was identified at 7p22.2p22.1, which is the likely cause of this individual's phenotype.On the X chromosome, a 5.3 Mb terminal pathogenic deletion at Xq28 and a 2.6 Mb terminal duplication of Xp22.33 overlapping PAR1 was called by the analysis pipeline.Manual review of array data revealed the presence of Yp material which included the SRY gene.The chromosomal sex was predicted to be female by the analysis software, and the gain of Yp was not flagged.This is likely due to the PAR regions being displayed on the X chromosome, regardless of whether it originates from the X or Y chromosome.This suggests the PAR1 gain was from the Y chromosome indicative of a translocation.Karyotype analysis confirmed a derivative chromosome X from an X;Y translocation [46,X,der(X)t(X;Y)(q28;p11.2)].