ERBB3 and cerebellar ataxia: Expression of NKG2D ligands is primarily regulated by the ataxia‐telangiectasia‐mutated, ataxia‐telangiectasia‐mutated, and Rad‐3‐related protein kinase pathways26 and is also up‐regulated by HER3 or EGFR signaling via the downstream pathway of PI3K/AKT.9, 10, 27