Mutant __SP__ __NODE__ gene ( unspecified homozygous gene mutation ) decreases phosphorylation of __SP__ __NODE__ protein in fibroblast cell lines from __SP__ exhibiting ataxia telangiectasia to phosphorylated __SP__ __NODE__ protein in fibroblast cell lines from __SP__ exhibiting ataxia telangiectasia that is increased by __NODE__ protein in culture medium .