Breakpoint mapping of a novel de novo translocation t(X;20)(q11.1;p13) by positional cloning and long read sequencing

Disease associated chromosomal rearrangements often have break points located within disease causing genes or in their vicinity. The purpose of this study is to characterize a balanced reciprocal translocation in a girl with intellectual disability and seizures by positional cloning and whole genome sequencing. The translocation was identification by G- banding and confirmed by WCP FISH. Fine mapping using BAC clones and whole genome sequencing using Oxford nanopore long read sequencing technology for a 1.46 X coverage of the genome was done. The positional cloning showed split signals with BAC RP11-943 J20. Long read sequencing analysis of chimeric reads carrying parts of chromosomes X and 20 helped to identify the breakpoints to be in intron 2 of ARHGEF9 gene on Xp11.1 and on 20p13 between RASSF2 and SLC23A2 genes. This is the first report of translocation which successfully delineated to single base resolution using Nanopore sequencing. The genotype-phenotype correlation is discussed.