A single splice - site variant ( 12 - 40626187 - T - C ) , found in 77 gnomAD carriers , was identified in an individual with RNA - seq data in the GTEx project . The RNA - seq reads were manually inspected to look for any effect on splicing . Assessing the read distribution of a linked heterozygous variant in this individual showed convincingly that the variant has no discernible effect on transcript splicing ( Extended Data Fig . 3 ) . All available tissues were assessed with reads from lung tissue shown in Extended Data Fig . 3 . The variant was also identified in eight UK Biobank carriers and in 23andMe and was similarly excluded from these cohorts .