Large genomic deletions and rearrangements in the TSC2 gene are also relatively common and are seen in about 6% of unselected TSC patients.30 In contrast, large genomic deletions are quite rare in TSC1 and are seen in only about 0.5% of unselected cases.1, 30 This may be due, in part, to a sequence within the adjacent PKD1 gene that blocks the replication fork and could lead to double-strand breaks in this region of chromosome 1634. Here, TSC1 is linked to tuberous sclerosis.