C9orf72 and dementia: Moreover, most FLCN mutations isolated from BHD patients are loss of function leading to decreased protein stability or inability to interact with FNIP1/2 (Schmidt and Linehan, 2018), likewise the C9orf72 repeat expansion found in ALS and dementia cases results in a loss of function due to reduced C9orf72 protein expression (Waite et al., 2014).