OPHN1 and Intellectual disability: In fact, mutations in some genes implicated in mental retardation, such as fragile X mental retardation 1 gene, oligophrenin 1, p21-activated kinase, and rho guanine nucleotide exchange factor 6, have been found to directly and indirectly affect laminar organization, axonal guidance, and proper connectivity [1], [38], [40], which, in turn, might have an effect on the cortical thickness in patients with mental retardation.