NF1 and neurofibromatosis type 1: The latter would, however, be in conflict with a slight majority of studies that concluded that T2Hs associated with NF1 have a negative impact cognitive ability.39–42 However, if the presence of T2Hs shows a high concordance within 11 NF1 MZ twin pairs as previously suggested,12 it is debatable whether presence of T2Hs should be considered a nongenetic factor in the first place.