Another important consideration is the relative timing of
gene loss in different tissues. Adult-onset ciliopathy can result
from the spontaneous loss of heterozygosity of a ciliary gene in
patients carrying one mutant allele. This second hit would occur
long after embryogenesis; thus, developmental defects such as
polydactyly would not be seen. Timing of ciliopathy onset can be
studied using inducible Cre-mediated knockout alleles ( Garcia-
Gonzalez et al., 2007 ).