Two siblings with osteogenesis imperfecta have normal parents. The mode of inheritance is explained by which of the following?

Gonadal mosaicism Mutation that occurs during early embryonic development. If the mutation affects only cells destined to form the gonads, the gametes carry the mutation, but the somatic cells of the individual are completely normal. Such an individual is said to exhibit germ line or gonadal mosaicism. A phenotypically normal parent who has germ line mosaicism can transmit the disease-causing mutation to the offspring through the mutant gamete. Since the progenitor cells of the gametes carry the mutation, there is a definite possibility that more than one child of such a parent would be affected. Eg :Tuberous sclerosis and Osteogenesis Imperfecta.