A patient recently reported to harbor a missense variant of PGK1 (c.649G > A, p.Val217Ile) and intellectual disability, mild cerebral and cerebellar atrophy and peculiar episodes of muscle weakness of unknown etiology, but without hemolytic anemia, had a residual enzymatic activity of 78–91% in RBCs [38]. This evidence concerns the gene PGK1 and Intellectual disability.