Numerical Aberration

• Numerical abnormalities involve defects in the number of chromosomes
• Euploidy is the condition of having a normal number of structurally normal chromosomes
• Aneuploidy is any abnormal number of chromosomes that is not a multiple of the haploid number (23 chromosomes)
• Aneuploidy is a result of nondisjunction, which is the failure of chromosomes to separate normally during cell division (meiosis)
• Trisomy is the presence of an extra chromosome, while monosomy is the absence of a single chromosome
• Polyploidy is when the chromosome number is higher than 46 but is always an exact multiple of the haploid chromosome number of 23
• Triploidy (3n) is a karyotype with 69 chromosomes, and tetraploidy (4n) is a karyotype with 92 chromosomes
• Autoploidy can occur through nondisjunction (meiotic and mitotic) or genome duplication
• Other terms for numerical abnormalities include hypodiploid, near-haploid, hyperdiploid, and high hyperdiploidy
• Disease associations of numerical abnormalities include infertility, sterility, intersexes, multiple congenital malformations, and mental retardation
• Sex chromosome aneuploidies:

  • Females: Turner Syndrome (XD), Metafemale (Triple-X)
  • Males: Klinefelter syndrome (XXY), Jacob syndrome (XYY)
• Monosomy and trisomy are associated with Turner syndrome, Klinefelter syndrome, Metafemale syndrome, and Jacob syndrome
• Turner Syndrome (XO) is characterized by gonadal dysgenesis, monosomy X, Ulirich-Turner syndrome, and specific physical features
• Triple X Syndrome (XXX) features an extra X chromosome in females, with menstrual irregularities and increased risk of learning disabilities
• Klinefelter’s Syndrome (XXY) is characterized by small firm testicles, low testosterone, incomplete masculinization, and other physical features
• Jacob’s Syndrome (XYY) features a normal phenotype, tall stature, increased vulnerability to ADHD, learning disabilities, and infertility
• Autosomal numeric aberrations include Down Syndrome, Edward Syndrome, Patau Syndrome, and Warkany Syndrome
• Down Syndrome (Trisomy 21) is caused by the presence of an extra 21st chromosome and features specific physical characteristics
• Edward Syndrome (Trisomy 18) is characterized by an extra 18th chromosome and specific physical features with a low survival rate
• Patau Syndrome (Trisomy 13) features an extra copy of chromosome 13 and specific physical and mental abnormalities
• Warkany Syndrome (Trisomy 8) is characterized by an extra chromosome 8 and specific physical features including facial characteristics, brain malformations, and other abnormalities