So, i was thinking that a potential mutation that could be added is Eczema.

Its a skin condition that often causes rashes, and the severity can vary from mild to severe.
In animals, it can cause patches where no fur grows due to the irritation of the skin.

There could be two types of eczema added.

Eczema: Mild - Small patches of fur loss mainly around joints, where it shows the skin colour underneath. No sores.
Eczema: Severe - Large patches of fur loss, showing the skin colour underneath. Sores and scabs visible. Split skin around joints. Lethal, due to the fact that the sores could get infected and being wild animals, survival can be pretty slim when infection sets in.

While there are many tpes of eczema, i figured just a sort of a broad across the board sort of type would be more effective than trying to match to every type that is out there.