Two siblings with osteogenesis imperfect, but their parents are normal. Mechanism of inheritance is aEUR’
**Core Concept**
Osteogenesis imperfecta is a genetic disorder characterized by brittle bones, blue sclerae, and hearing loss. It is caused by mutations in the COL1A1 or COL1A2 genes, which code for type I collagen. This condition is inherited in an autosomal dominant pattern, meaning a single copy of the mutated gene is sufficient to cause the condition.
**Why the Correct Answer is Right**
The correct answer is **D**. This is because osteogenesis imperfecta can be caused by a de novo mutation, which is a spontaneous mutation that occurs in one of the two copies of a gene in an individual. This means that the mutation did not come from either parent, but rather occurred for the first time in the affected individual. In this case, the siblings inherited the de novo mutation from their affected parent, who was the one who actually carried the mutation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because autosomal recessive inheritance would require both parents to be carriers of the mutated gene, which is not the case here.
**Option B:** This option is incorrect because X-linked dominant inheritance would require the mutated gene to be located on the X chromosome, which is not the case for osteogenesis imperfecta.
**Option C:** This option is incorrect because autosomal recessive inheritance would require both parents to be carriers of the mutated gene, which is not the case here.
**Clinical Pearl / High-Yield Fact**
It's worth noting that de novo mutations can occur in any gene, and can be responsible for a wide range of genetic disorders. This is an important consideration in genetic counseling and diagnosis.
**Correct Answer: D. De novo mutation**