An effected male infant born to normal parents could be an example of all of the following, except
**Core Concept**
The question pertains to the concept of genetic disorders, specifically those that can arise in the absence of a family history of the condition. This involves understanding the principles of Mendelian genetics, including autosomal dominant, autosomal recessive, and X-linked inheritance patterns.
**Why the Correct Answer is Right**
The correct answer involves identifying a condition that does not typically present as an isolated case without a family history. This requires an understanding of the genetic basis of the conditions listed as options. For example, conditions like cystic fibrosis and sickle cell anemia are often inherited in an autosomal recessive pattern, meaning that a child can only be affected if both parents are carriers of the mutated gene.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it refers to a condition that can indeed occur in the absence of a family history. This condition is often caused by a new mutation in one of the parents' genes, which can then be passed on to the child.
* **Option B:** Similarly, this option is also incorrect. This condition is often inherited in an autosomal dominant pattern, meaning that a single copy of the mutated gene is sufficient to cause the condition. However, new mutations can also occur, leading to isolated cases without a family history.
* **Option C:** This option is incorrect because it refers to a condition that is often caused by a combination of genetic and environmental factors. While there may be a family history of the condition, it is not necessarily the case that the affected individual has a mutated gene.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that even in the absence of a family history, genetic disorders can still occur due to new mutations or other genetic factors.
**Correct Answer: A. This option refers to a condition that can indeed occur in the absence of a family history.**