Homozygotes for FRA16B are normal

Homozygotes for the rare folate-sensitive autosomal fragile sites have neve r been recorded. Two non-folate-sensitive rare fragile sites (FRA10B and FR A17A) have been previously recorded in normal individuals. We document two unrelated normal individuals who are homozygotes for the rare fragile site FRA16B and record the patterns of induction of this fragile site with beren il. The existence of normal homozygotes for FRA16B suggests that this fragi le site is not within a gene essential for normal development.