**Core Concept**
Testicular feminisation syndrome, also known as complete androgen insensitivity syndrome (CAIS), is a condition where individuals with 46 XY karyotype are resistant to androgens, resulting in the development of female external genitalia despite the presence of testes. This condition is caused by mutations in the androgen receptor gene, leading to the inability of androgens to bind to their receptors.

**Why the Correct Answer is Right**
Primary amenorrhea is a characteristic feature of testicular feminisation syndrome. Individuals with CAIS have a vagina, but it is usually short and narrow due to the lack of androgen stimulation during fetal development. The absence of androgenic stimulation also leads to the absence of Müllerian duct development, resulting in the absence of a uterus and fallopian tubes. As a result, individuals with CAIS typically experience primary amenorrhea, as they do not have the necessary reproductive organs to support menstrual cycles. The presence of testes and the absence of ovaries in individuals with CAIS lead to the production of testosterone, which can cause virilization of the body, but the androgen receptor dysfunction prevents the effects of testosterone on the body, resulting in a female phenotype.

**Why Each Wrong Option is Incorrect**
**Option A:** Individuals with testicular feminisation syndrome have a 46 XY karyotype, not 46 XX, which is characteristic of typical female development.

**Option B:** While individuals with CAIS may have a short, narrow vagina, it is not the defining feature of the condition. The presence of a vagina is not exclusive to individuals with CAIS and can be present in other conditions as well.

**Option D:** Short stature is not a characteristic feature of testicular feminisation syndrome. Individuals with CAIS typically have a normal height and may exhibit other physical characteristics, such as a female body habitus and sparse or absent axillary and pubic hair.

**Clinical Pearl / High-Yield Fact**
Individuals with testicular feminisation syndrome may undergo surgical removal of the testes and hormonal therapy to develop a more feminine appearance. However, they are at an increased risk of developing gonadal tumors, particularly in the undescended testes.

✓ Correct Answer: C. Primary amenorrhea