A non-allelic homologous recombination-induced inversion in intron 22 of the F8 gene is causative for haemophilia A in a Weimaraner male dog

Haemophilia A is a severe coagulation disorder caused by partial or complete loss of function of the X-chromosomal F8 gene. It is a relatively common coagulation disorder that has been reported in at least 17 dog breeds to date. However, only five distinct molecular causes have been identified so far. One molecular genetic cause is a large inversion, which has also been described in humans and was first studied in a research colony of Irish Setters at the University of North Carolina at Chapel Hill. However, the exact location of the inversion breakpoint junctions in dogs has not been determined. Here, we describe the molecular analysis of a case of haemophilia A in a Weimaraner dog family using long-read sequencing. We show that the cause of haemophilia A is an approximately 420kb inversion affecting the F8 gene. The breakpoints of the inversion were identified in intron 22 at position 124,003,000 and between chloride intracellular channel 2 (CLIC2) and epsilon-trimethyllysine hydroxylase (TMLHE) at position 124,432,668 (NC_049260.1:g.124003000_124432668inv). As in humans, the inversion is most likely caused by non-allelic homologous recombination between intron 22 and a region approximately 420kb downstream of the F8 gene. By identifying the inversion breakpoint junctions, it is now possible to test carriers of the disorder at the DNA level and thus prevent the risk of disease in male offspring.