In a girl with sexual infantilism and defective smell sensation which of the following is the likely diagnosis transmitted by sex chromosome?
## **Core Concept**
The question involves a genetic disorder affecting sexual development and olfaction (smell sensation), with a transmission pattern related to sex chromosomes. The disorder in question likely affects the X chromosome, given the mention of transmission by sex chromosome.
## **Why the Correct Answer is Right**
The correct answer, **Kallmann Syndrome**, is a genetic disorder characterized by delayed or absent puberty (sexual infantilism) and an impaired sense of smell. This condition is caused by mutations in genes involved in the development of the hypothalamic-pituitary-gonadal axis and the olfactory system. Kallmann Syndrome is often inherited in an X-linked recessive pattern, which means the gene responsible for the condition is located on the X chromosome. This pattern explains the higher prevalence in males, who have one X chromosome, but females can be carriers.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Turner Syndrome is characterized by short stature, gonadal dysgenesis, and other physical features, but it does not primarily involve defective smell sensation. It is indeed transmitted by a sex chromosome abnormality (45,X).
- **Option B:** Androgen Insensitivity Syndrome (AIS) involves sexual infantilism due to resistance to androgens but does not typically involve impaired olfaction. AIS is transmitted in an X-linked recessive pattern.
- **Option D:** No information provided.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Kallmann Syndrome is a rare cause of delayed puberty and is distinguished from other causes by the presence of anosmia (loss of the sense of smell). This combination of hypogonadotropic hypogonadism and anosmia is pathognomonic for Kallmann Syndrome.
## **Correct Answer: C. Kallmann Syndrome**