**Question:** A 20-year-old female presents for an infertility workup. She has never had a menstrual period. She is short with a broad chest, webbed neck, and low-set ears. It is demonstrated that she has an abnormal karyotype. The cause of the woman's abnormal karyotype is which one of the following?

A. Turner's syndrome
B. Klinefelter's syndrome
C. Marfan's syndrome
D. Nocturnal enuresis

**Correct Answer:** **A. Turner's syndrome**

**Core Concept:** Turner's syndrome is a genetic disorder characterized by partial or complete monosomy X (45,X karyotype) in females. It results in a range of clinical manifestations, including primary amenorrhea, short stature, webbed neck, low-set ears, and growth deficiency.

**Why the Correct Answer is Right:** Turner's syndrome occurs due to the absence of one X chromosome in females, leading to incomplete development of secondary sexual characteristics, including menstruation and reproductive organs. The clinical features mentioned in the question align with the typical manifestations of Turner's syndrome.

**Why Each Wrong Option is Incorrect:**

**A. Klinefelter's syndrome:** This is a genetic disorder characterized by an extra X chromosome (47,XXY karyotype) in males. It presents with primary amenorrhea in females is incorrect.

**B. Marfan's syndrome:** This is a connective tissue disorder affecting multiple systems, including the cardiovascular, skeletal, and ocular systems. It is not related to primary amenorrhea or the other clinical features mentioned in the question.

**C. Marfan's syndrome:** Similar to option B, Marfan's syndrome is not related to primary amenorrhea or the clinical features mentioned in the question.

**D. Nocturnal enuresis:** Nocturnal enuresis is the involuntary urination during sleep, typically seen in children and not related to primary amenorrhea or the clinical features mentioned in the question.

**Core Concepts:** Turner's syndrome, X-chromosome, primary amenorrhea, secondary sexual characteristics, and clinical features

**Clinical Pearls:** Understanding the role of X-chromosomes in sexual development and the clinical features mentioned in the question is essential for diagnosing Turner's syndrome accurately. Turner's syndrome should be considered in females with primary amenorrhea and clinical features such as short stature, webbed neck, low-set ears, and other skeletal abnormalities.