ERBB4 and frontotemporal dementia: The presence of circulating ERBB4 ectodomain fragments (specifically 55 kDa and 80 kDa) in the cerebrospinal fluid and plasma of both ALS and ALS-FTD patients has been confirmed, with levels found to be decreased compared to controls and absent in the plasma of ERBB4 knockout mice (Lopez-Font et al., 2019).