Homozygotes for FRA16B are normal.

Homozygotes for the rare folate-sensitive autosomal fragile sites have never been recorded. Two non-folate-sensitive rare fragile sites (FRA10B and FRA17A) 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 berenil. The existence of normal homozygotes for FRA16B suggests that this fragile site is not within a gene essential for normal development.