ERBB4 and mild neurocognitive disorder: In contrast, more easily available patient-derived cell types like fibroblasts and PBMCs do not express several relevant MND genes like SPG10 (KIF5A), SPG26 (B4GALNT1), SPG31 (REEP1), ERBB4 and PLEKHG5 and therefore disqualify as cellular models for pathogenic studies in these MNDs.