ARID1A and neoplasm: Chromosome 1p contains several genes with important biologic functions in neuroblastoma, including CHD5, CASZ1, ARID1A, and MTOR (Fig 3B-3E).27 Increased 5-hmC was also detected in several additional genes in tumors with chromosome 1p loss, including tumor-promoting genes ABCG1 and S100B mapping to chromosome 21q.