Turner Syndrome

Introduction

• Definition: Turner syndrome is a chromosomal disorder affecting females, where one X chromosome is either completely or partially absent.
• Named after: Henry Turner, who first described it.
• Chromosomes: Normally, humans have 46 chromosomes - 23 pairs. In Turner syndrome, an X chromosome is missing or incomplete.

Chromosomal Background

• Normal Chromosomal Arrangement:
  • 23 pairs of chromosomes, each pair has one chromosome from each parent.
  • Sex chromosomes determine biological sex: XX for females, XY for males.
• Meiosis and Chromosomal Contribution:
  • Meiosis is crucial for producing sex cells (sperm/egg).
  • Errors during meiosis can lead to monosomy (one chromosome less in a pair), causing Turner syndrome.

Genetic Scenarios in Turner Syndrome

• Common Karyotypes:
  • 45,X: Completely missing an X chromosome.
  • Mosaicism: Some cells are 45,X and others are 46,XX. Occurs due to post-conception errors.
  • Partial Deletion: Part of the X chromosome is missing.
• Non-disjunction: Failure of chromosomes to separate properly during meiosis or mitosis.

Clinical Manifestations

• Reproductive System:
  • Increased rate of egg loss, leading to early menopause.
  • Non-functional streak ovaries, causing hypogonadism and low estrogen.
• Growth and Development:
  • Short stature due to a single copy of SHOX gene.
• Other Health Issues:
  • Cardiovascular defects: Coarctation of the aorta, bicuspid aortic valve.
  • Renal issues: Horseshoe kidney.
  • Increased risk for type 2 diabetes and hypothyroidism.
  • Lymphatic and skeletal abnormalities.

Symptoms and Diagnosis

• Symptoms Vary With Age:
  • Infants: Lymphedema, cystic hygroma, neck webbing.
  • Children/Adolescents: Short stature, broad chest, skeletal abnormalities.
  • Adolescents: Primary amenorrhea and infertility.
• Diagnosis:
  • Karyotype analysis via chorionic villus sampling or amniocentesis.
  • Ultrasound and other tests for developmental abnormalities.

Treatment

• Growth Hormone Therapy: To promote height and bone growth in childhood.
• Sex Hormone Replacement Therapy: Starting in adolescence to promote development.
• Fertility Treatments: In vitro fertilization might help some with Turner syndrome achieve pregnancy.

Summary

• Turner syndrome involves a complete or partial absence of an X chromosome.
• Common features include streak ovaries, short stature, and congenital heart/renal defects.
• Treatment involves hormone therapies to address growth and reproductive issues.