Turner syndrome

Intro & Genetics - XO Marks the Spot

• Most common chromosomal disorder in females, affecting ~1 in 2,500 live births.
• Results from the complete or partial absence of one X chromosome.

• Karyotypes:
  • Classic Monosomy X ($45,X$): ~50% of cases. Due to meiotic nondisjunction.
  • Mosaicism ($45,X/46,XX$): ~30-40%. Often results in a milder phenotype.
  • Structural X chromosome abnormalities (e.g., isochromosome Xq, ring chromosome).
• 📌 Paternal X chromosome is lost in ~80% of monosomy cases.

⭐ The SHOX gene (Short-stature Homeobox) on the distal tip of the X chromosome is haploinsufficient, leading to the characteristic short stature.

Clinical Features - Short Stature, Big Signs

📌 CLOWNS: Cardiac, Lymphedema, Ovaries, Webbed neck, Nails, Short stature.

• General Appearance
  • Short stature: Universal finding; average adult height ~143 cm.
  • Stocky build, shield-like chest with widely spaced nipples.
• Head & Neck
  • Low posterior hairline.
  • Webbed neck (pterygium colli).
  • High-arched palate, retrognathia.
• Limbs & Skin
  • Cubitus valgus (increased carrying angle).
  • Madelung deformity of the wrist.
  • Hyperconvex, deep-set nails.
  • Congenital lymphedema of hands & feet in newborns.
• Cardiac
  • Coarctation of the Aorta.
  • Bicuspid aortic valve.

⭐ High-Yield Fact: The most common cardiac anomaly in Turner Syndrome is a bicuspid aortic valve, present in up to 30% of patients, followed by coarctation of the aorta.

Diagnosis & Workup - Finding the Missing Piece

• Prenatal:
  • Screening: ↑ Nuchal translucency, NIPT.
  • Definitive: Amniocentesis/CVS for fetal karyotyping.
• Postnatal (Gold Standard):
  • Karyotyping confirms diagnosis (45,X).
  • FISH can detect mosaicism.

• Systemic Screening:
  • Cardiac: Echo/MRI (Bicuspid Aortic Valve, Coarctation).
  • Renal: Ultrasound (Horseshoe Kidney).
  • Endocrine: TFTs, Glucose.
  • Sensory: Audiology & Ophthalmology eval.

⭐ High-Yield: The presence of any Y-chromosome material in mosaic Turner Syndrome (e.g., 45,X/46,XY) necessitates prophylactic gonadectomy due to a high risk of gonadoblastoma.

Management - Growing & Glowing Up

• Growth Promotion:

  • Recombinant Human Growth Hormone (rhGH) is the mainstay.
  • Goal: ↑ final height by 8-10 cm.
  • Often started as soon as growth failure is noted.

• Pubertal Induction (Feminization):

  • Initiate low-dose unopposed estrogen at age 11-12 years to mimic puberty.
  • Add progestin later (after 1-2 yrs or on breakthrough bleeding) to induce cycles & protect endometrium.

⭐ Estrogen therapy is vital not just for secondary sexual characteristics, but for uterine development, achieving peak bone mass, and preventing future osteoporosis.

High-Yield Points - ⚡ Biggest Takeaways

• The classic karyotype is 45,X, most often due to paternal meiotic nondisjunction.
• Cardinal features include short stature (most consistent finding), streak gonads, webbed neck, and a shield chest.
• The most common cardiac defect is a bicuspid aortic valve, followed by coarctation of the aorta.
• Horseshoe kidney is the most frequent renal anomaly.
• Presents as primary amenorrhea with low estrogen and high FSH/LH levels.
• Intelligence is generally normal.