PSENEN and histiocytic sarcoma: In a U.K. study conducted by Pink et al. in 2011 [12], 53 individuals from seven multigenerational pedigrees were enrolled and the screening of NCSTN, PSEN1, and PSENEN genes did not reveal pathogenic variants in five out of the seven pedigrees examined; moreover, in a French study [11], only three out of fourteen pedigrees revealed the causative involvement of GSC genes, and similarly, mutational analysis of NCSTN, PSEN1, and PSENEN in twenty familial HS patients referred to a tertiary U.K. clinic, detected only two pathogenic variants in the coding region and splice site of NCSTN gene [13].