Steps to reproduce:
Create a new patient, go to the "Genotype information" section
Enter a gene
Add a variant. Notice how the gene name becomes "locked" (can no longer be edited)
Save & view
Result: the gene name is now editable, and will remain that way until another variant is added. If the user changes the gene name, all variants that were linked to the previous gene name will "disappear" upon saving the document (while the data is still there, they are not shown in the UI since theu are thought to belong in a different gene).
In the absence of a mechanism to propagate the new gene name to the existing variants, the expected behavior would be to not allow the gene name to be edited when there are already variants associated. This would be consistent with the behavior displayed the first time the user enters the gene and its variants.