Lecture Notes: Turner Syndrome

Introduction

• Named after Henry Turner, who first described it.
• Chromosomal disorder affecting females.
• Involves the complete or partial absence of one X chromosome.

Chromosomal Basics

• Humans have 46 chromosomes in 23 pairs.
• Sex chromosomes determine biological sex: XX for females, XY for males.
• Formation of sperm and egg cells involves meiosis, reducing chromosome number to 23.

Turner Syndrome and Chromosomal Anomalies

• Monosomy: Missing one chromosome, specifically affects the X chromosome in Turner syndrome.
• Common Karyotype Scenarios:
  1. 45X Karyotype: Entire X chromosome is missing.
  2. Mosaicism: Mix of 45X and 46XX cells due to post-conception error.
  3. Partial X Chromosome Deletion: Only part of the X chromosome is missing.

Causes of Turner Syndrome

• Result of non-disjunction during meiosis.
• Errors during mitosis contribute to mosaic karyotypes.
• Non-disjunction can lead to one cell with too many chromosomes and another with too few.

Impact on the Female Reproductive System

• Increased rate of egg loss, leading to early menopause.
• Ovaries don't develop properly, resulting in "streak ovaries".
• Low estrogen levels due to non-functional ovaries.
• High levels of FSH and LH due to low estrogen.

Effects on Growth and Development

• Short stature: Due to a single copy of the SHOX gene.
• Cardiovascular defects like coarctation of the aorta and bicuspid aortic valve.
• Kidney issues, e.g., horseshoe kidney.
• Higher risk for type 2 diabetes and hypothyroidism.

Signs and Symptoms

• Symptoms vary by age and extent of X chromosome loss.
• Infancy: Lymphedema, neck webbing, potential heart issues.
• Adolescence: Short stature, broad chest, skeletal abnormalities, primary amenorrhea.

Diagnosis

• Karyotype analysis for definitive diagnosis.
• Prenatal testing via chorionic villus sampling or amniocentesis.
• Other tests: Ultrasound and fasting blood glucose test for specific abnormalities.

Treatment

• Growth hormone therapy: Promotes height and bone growth.
• Sex hormone replacement therapy: For breast and uterine development.
• In vitro fertilization: Possible for some females to achieve pregnancy.

Summary

• Turner syndrome is characterized by missing or partially absent X chromosome.
• Main features include streak ovaries, short stature, and congenital defects.
• Treatment focuses on growth, development, and addressing specific symptoms.

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Note: Always consult with a healthcare professional for a thorough understanding and personalized medical advice.