Adaptive long-read and transcriptome sequencing detail a submicroscopic inv(15)(q14q15), generating fusion transcripts and MEIS2 and NUSAP1 haploinsufficiency

Inversions are balanced structural variants that often remain undetected in genetic diagnostics. We present a female proband with a de novo Chromosome 15 paracentric inversion, disrupting MEIS2 and NUSAP1 . The inversion was detected by short-read genome sequencing and confirmed with adaptive long-read sequencing. The breakpoint junction analysis revealed a 96 base pair (bp) deletion and an 18 bp insertion in the two junctions, suggesting that the rearrangement arose through a replicative error. Transcriptome sequencing of cultured fibroblasts revealed normal MEIS2 levels and 0.61-fold decreased expression of NUSAP1 . Furthermore, two fusion transcripts were detected and confirmed by Sanger sequencing. Heterozygous loss of MEIS2 (MIM# 600987) is associated with a cleft palate, heart malformations, and intellectual impairment, which overlap with the clinical symptoms observed in the proband. The observed fusion transcripts are likely non-functional, and MEIS2 haploinsufficiency is the likely disease causative mechanism. Altogether, this study findings illustrate the importance of including inversions in rare disease diagnostic testing and highlight the value of long read sequencing for the validation and characterization of such variants.