REXO2 and neoplasm: However, firm conclusions cannot be drawn from this single family: the lack of available tumour tissue to test for allelic loss or immunostaining for loss of protein expression, the lack of an animal model to conclusively show the causal role of this gene variant in PCC, the existence of other REXO2 variants affecting the same splice site and the fact that no other PCC families were reported to harbour mutations in this gene should be taken into consideration.