Klinefelter syndrome and sex chromosome aneuploidy — formative SAQs

SAQ 1 (10)

A fourteen-year-old boy is referred by his school counsellor for academic underachievement, social withdrawal, and concern that puberty has not started. On examination he is tall with eunuchoid proportions, has mild gynaecomastia, and his testicular volume is 4 mL bilaterally. A karyotype is requested and returns 47,XXY. [1] [2]

a) Define Klinefelter syndrome and explain why the chromosomal mechanism — a karyotype rather than a chromosomal microarray — is essential for diagnosis and counselling. (3 marks) [1]

b) Describe the endocrine investigation profile you expect, including the expected pattern of LH, FSH, testosterone, and inhibin B. Explain the pathophysiology underlying this profile. (3 marks) [2] [3]

c) Outline the lifespan surveillance framework for this young man, covering testosterone replacement, bone health, metabolic risk, fertility, and psychosocial support. (3 marks) [4] [3]

d) The family asks whether he will be able to have biological children. Explain the role of micro-TESE (microsurgical testicular sperm extraction) and the approximate success rate, and how this changes the counselling. (1 mark) [2] [4]

SAQ 2 (10)

A thirty-two-year-old man presents to the emergency department with a swollen, painful right leg. Doppler ultrasound confirms a deep vein thrombosis. He is tall, has a history of learning difficulties and left school at fifteen, and has small testes on examination. A karyotype subsequently confirms 47,XXY. [3] [1]

a) Explain the association between Klinefelter syndrome and venous thromboembolism, including the estimated risk increase and the mechanism. (3 marks) [3]

b) Describe the metabolic and cardiovascular complications of Klinefelter syndrome that this man should be screened for, and outline the baseline investigations. (3 marks) [3] [1]

c) If this man is found to have low testosterone with elevated LH and FSH, outline the principles of testosterone replacement, including the monitoring required for safety. (2 marks) [4]

d) A separate family is referred for counselling after a cell-free DNA screen flagged a possible sex chromosome aneuploidy. Outline the key counselling messages, including the limitations of cell-free DNA and the importance of the prospective phenotype data from the eXtraordinarY babies study. (2 marks) [5] [1]