That sounds like a very inaccurate necropsy (or maybe just a vague recollection and conveyance of it) as any number of things can cause kidney issues... including excess calcium or protein. Some things are even genetic.We didn;t get any paper. The vet didn't know what disease it was, he only knew that it had to do something with virus as kidneys (i think) were swollen. I noticed that the laying one makes a gurgling sound sometimes.
Gurgling sound.. fluid build up in the lungs.. *possibly*.. is one effect of kidney failure.. ultimately leading to what's called congestive heart failure. Would be indicated by age, feed, and other symptoms..
But the poultry site link I provided shows kidney damage being a symptom of SOOOO many things depending on exactly what type of damage is seen under the microscope ( a key to pathology for necropsy IMO).. so take your time and read through them see what most fits..
How many birds have ya got total? Did the vet make any recommendations for future additions, vaccines, or anything like that? What is the age we are talking about them passing here?