What is Turner syndrome?

What is Turner Syndrome

Turner syndrome is a genetic condition in females caused by complete or partial loss of one X chromosome, affecting approximately 1 in 2,500 liveborn girls, and characterized by short stature, ovarian dysgenesis, cardiovascular malformations, and increased risk of multiple endocrine and autoimmune disorders. 1, 2

Genetic Basis

• Turner syndrome results from complete monosomy X (45,X) in 40-50% of cases, with the remaining cases showing various mosaic karyotypes including monosomy X mosaicism, isochromosome X, ring X chromosomes, or Y chromosome material 3
• The paternal X chromosome is absent in approximately 75% of cases, though this finding has no clinical utility in routine care 3
• Pregnancy loss occurs in approximately 99% of Turner syndrome cases, making liveborn cases relatively rare 3

Cardinal Clinical Features

Growth and Stature

• Short stature is one of the two most prevalent findings in Turner syndrome, with SHOX gene deficiency explaining much of the height deficit 2, 4

Reproductive and Endocrine Manifestations

• Ovarian dysgenesis with hypergonadotropic hypogonadism and infertility represents the second most prevalent finding 1, 2
• Delayed puberty occurs in most patients, requiring induced puberty and lifelong hormone replacement therapy 1, 5
• Hypothyroidism occurs with increased frequency and requires regular screening 1
• Increased risk of both type 1 and type 2 diabetes mellitus 5, 6
• Osteoporosis risk is elevated 5, 7

Cardiovascular Abnormalities (Critical for Mortality)

• Bicuspid aortic valve occurs in 15-30% of patients 1, 2
• Aortic coarctation is present in 7-18% of cases 1, 2
• Ascending aortic dilation affects approximately 33% of patients 1, 2
• Aortic dissection at young age represents a major cause of increased cardiovascular mortality, with risk significantly higher than the general population 1, 2

Physical Dysmorphic Features

• Webbed neck (pterygium colli) is a classic visible stigmata 1
• Lymphedema of hands and feet, particularly prominent in infancy 1

Prenatal Presentation

• Cystic hygroma is associated with 50-80% of prenatally detected cases, resulting from lymphatic dysplasia 1
• Nonimmune hydrops fetalis may develop secondary to lymphatic dysplasia and cardiovascular malformations 1

Morbidity and Mortality Impact

• Women with Turner syndrome have increased cardiovascular mortality from both structural and ischemic heart disease, especially aortic dissection 2, 7
• Overall morbidity and mortality are clearly increased compared with the general population 5, 6
• Reduced life expectancy is primarily due to excess cardiovascular risk 7
• Multiple comorbidities including autoimmune disorders contribute to increased morbidity 1, 5

Diagnostic Considerations

• Despite often conspicuous phenotype, diagnostic delay is substantial with average age at diagnosis around 15 years 5
• All patients require baseline cardiovascular imaging with transthoracic echocardiography and cardiac MRI at diagnosis to evaluate for life-threatening cardiovascular abnormalities 1, 2

Critical Management Pitfall

• A critical error is underestimating aortic dissection risk in patients with small body size—always use indexed measurements (aortic size index) or Turner-specific z-scores rather than absolute measurements 1, 8
• Failure to perform baseline cardiac MRI at diagnosis misses important structural abnormalities not visible on echocardiography alone 1