Klinefelter syndrome (KS) is the most common sex chromosome disorder in males, caused by the presence of one or more extra X chromosomes.
• Classic karyotype: 47,XXY (about 80–90% of cases)
• Phenotypic sex: Male
• Characterized by:
o Primary testicular failure, Hypergonadotropic hypogonadism
o Infertility, Tall stature
o Variable neurodevelopmental and psychosocial features
Epidemiology- Incidence: 1 in 500–650 live male births
Cause - Usually caused by meiotic nondisjunction.
Pathophysiology
One X chromosome is largely inactivated (Barr body), but many genes escape X-inactivation, leading to abnormal gene dosage.
This results in:
• Seminiferous tubule degeneration, Leydig cell dysfunction
• Progressive fibrosis of the testes, Reduced testosterone production
• Elevated gonadotropins (LH and FSH)
Clinical Features
Infancy
• Hypotonia, Delayed motor milestones
• Feeding difficulties, Undescended testes
• Micropenis
Childhood
• Tall stature, long legs
• Learning difficulties, Language delay
• Poor reading skills, ADHD
• Mild motor incoordination, Shyness, Social difficulties
Adolescence
• Delayed or incomplete puberty
• Small, firm testes, Sparse facial and body hair
• Reduced muscle mass, Gynecomastia
• Eunuchoid body proportions
• Low libido, Fatigue
Adults
Reproductive
• Infertility, Azoospermia (most common)
• Reduced fertility, Erectile dysfunction (occasionally)
Endocrine
• Testosterone deficiency
• Osteoporosis, Decreased bone mineral density
• Reduced muscle mass
• Increased body fat, Metabolic syndrome
Psychological
• Anxiety, Depression, Reduced self-esteem
• Executive function deficits
• Autism spectrum traits in some individuals
Physical Examination
• Tall stature, Arm span > height, Long lower limbs
• Narrow shoulders, Broad hips
• Small testes (<4 mL)
• Gynecomastia, Sparse beard
• Sparse body hair, Decreased muscle bulk
Laboratory Findings
Hormonal Profile
| Test | Result |
|---|---|
| Testosterone | ↓ Low |
| LH | ↑ High |
| FSH | ↑ High |
| Estradiol | Mildly increased |
| Inhibin B | Low |
Semen Analysis
Usually shows: Azoospermia
Occasionally: Severe oligospermia
Complications Endocrine
• Diabetes mellitus, Metabolic syndrome
• Obesity, Dyslipidemia
Bone - Osteopenia, Osteoporosis, Fractures
Reproductive – Infertility, Erectile dysfunction
Autoimmune diseases
• Systemic lupus erythematosus, Rheumatoid arthritis
• Autoimmune thyroid disease, Sjögren syndrome
Venous disease
• Increased risk of deep vein thrombosis, Pulmonary embolism, Chronic venous insufficiency