MTAP and Huntington disease: Of the 49 cell lines with HD, 32 (65%) cell lines had the entire gene cluster at 9p21.3 locus (MTAP-CDKN2A-CDKN2B genes) deleted, 13 (27%) cell lines had deletions within MTAP or between MTAP and CDKN2A, and four (8%) cell lines had deletions within CDKN2A and 2B genes (Figure 3).