Turner Syndrome: Causes and Pathophysiology

What is the primary reason for short stature in individuals with Turner syndrome?

What is the hallmark of cardiovascular abnormalities in individuals with Turner syndrome?

What is a common musculoskeletal finding in individuals with Turner syndrome?

What is the primary purpose of karyotyping in individuals with Turner syndrome?

What is a common endocrine abnormality in individuals with Turner syndrome?

What is the approximate prevalence of Turner syndrome in the genetically female population in the US?

What is the most common cause of ovarian dysgenesis and primary ovarian insufficiency?

What is the karyotype of an individual with complete sex chromosomal monosomy?

What is the result of mitotic nondisjunction of an embryonic cell?

What is the fertility outcome for women with Turner syndrome who undergo IVF using donor oocytes and exogenous hormones?

Epidemiology

Prevalence of Turner syndrome: approximately 1 in 2,500 genetically female individuals in the US

Etiology

Caused by chromosomal nondisjunction during meiosis or mitosis
Meiotic nondisjunction: complete sex chromosomal monosomy (45,XO; no Barr body)
Mitotic nondisjunction of an embryonic cell: sex chromosomal mosaicism (45,XO/46,XX) with mild phenotypic expression

Pathophysiology

Chromosomal nondisjunction → X chromosome monosomy/mosaicism
Impaired ovarian development → malfunctioning streak gonads with connective tissue instead of normal germ cells
Estrogen and progesterone deficiencies

Clinical Features

Female phenotype
Primary ovarian insufficiency with:
- Delayed puberty
- Primary amenorrhea
- Infertility (pregnancy possible via IVF with donor oocytes and exogenous estradiol 17β and progesterone)
Lymphatic system abnormalities:
- Cystic hygroma
- Lymphedema of the hands and feet in neonatal period
Musculoskeletal findings:
- Short stature (due to presence of only one copy of the SHOX gene)
- Shield chest
- Webbed neck
- Cubitus valgus
- Short fourth metacarpals/metatarsals
- Nail dysplasia
- High arched palate
- Low-set posterior hairline
Cardiovascular abnormalities:
- Bicuspid aortic valve
- Coarctation of the aorta with brachial-femoral delay
- Aortic dissection and rupture
- Hypertension

Associated Disorders

Gonadoblastoma (especially in patients with 45,XO/46,XY mosaicism)
Malformations of the kidney and ureters (especially horseshoe kidney)
Hashimoto thyroiditis
Type 2 diabetes mellitus

Diagnostics

Clinical presentation: hypergonadotropic hypogonadism (↓ estrogen, ↓ androgens, ↑ FSH, ↑ LH)
Karyotyping: confirmatory test

Treatment

Estrogen and progestogen substitution
Growth hormone (GH) therapy
Surgical removal of streak gonads

Learn about the prevalence, etiology, and pathophysiology of Turner syndrome, a chromosomal disorder affecting genetically female individuals. Understand the role of meiotic and mitotic nondisjunction in its development.