What is the Difference Between Trisomy 18 and 21?
🆚 Go to Comparative Table 🆚Trisomy 18 and Trisomy 21 are both genetic disorders that result from an extra copy of a chromosome, but they have distinct differences in their characteristics and outcomes. Here are the main differences between the two:
- Chromosomes involved: Trisomy 18 occurs when a baby has three copies of chromosome 18, while Trisomy 21, also known as Down syndrome, occurs when a baby has three copies of chromosome 21.
- Incidence: Trisomy 18 occurs in 1 in 5,000 births, while Trisomy 21 is more common, occurring in approximately 1 in 700 babies.
- Survival: Trisomy 18 is generally fatal, with 60% of affected children dying within two months and more than 95% dying within a year. In contrast, while Trisomy 21 is associated with intellectual disabilities and various health issues, many individuals with Down syndrome can live long, fulfilling lives.
- Risk factors: Both Trisomy 18 and Trisomy 21 can occur at any age, but the risk increases with the mother's age. However, the majority of babies born with Trisomy 21 are to parents younger than 35 years of age.
- Physical characteristics: Individuals with Trisomy 18 often have facial dysmorphism, micrognathia, low-set abnormal ears, hirsutism, and multiple organ system malformations such as spina bifida, omphalocoele, heart defects, clubfeet, and radial aplasia. In contrast, individuals with Trisomy 21 often have some characteristic physical features, such as a flattened facial profile, upward slanting eyes, and a single palmar crease.
In summary, Trisomy 18 and Trisomy 21 are both genetic disorders with different chromosomes involved, varying incidences, survival rates, risk factors, and physical characteristics. While both conditions are associated with intellectual disabilities and various health issues, the outcomes for individuals with Trisomy 21 are generally more favorable than those with Trisomy 18.
Comparative Table: Trisomy 18 vs 21
Here is a table comparing Trisomy 18 and 21:
| Feature | Trisomy 18 | Trisomy 21 |
|---|---|---|
| Caused by | Extra chromosome 18 | Extra chromosome 21 |
| Chromosomal | Chromosome 18 | Chromosome 21 |
| Prevalence | 1 in 5,000 births | 1 in 700 births |
| Survival | Most die within 1 year | Risk increases with maternal age |
| Clinical Manifestations | Characteristic facies, low birthweight, growth retardation, clenched hands with camptodactyly | Characteristic facies, growth retardation, low muscle tone, some cases with congenital heart disease and duodenal atresia |
| Prognosis | Poor, survival beyond first year is rare | Better than Trisomy 18, 95% survive past first year |
| Maternal Age Risks | Risk is constant for Trisomy 18 across maternal age, 1 in 11,000 for mothers under 20 and above 34 | Risk increases exponentially with maternal age, 1 in 1,250 for mothers younger than 25 and 1 in 100 for mothers older than 35 |
Both Trisomy 18 and 21 are chromosomal disorders caused by an extra chromosome, but they have different clinical manifestations and prognoses. Trisomy 18 is more life-threatening than Trisomy 21. The risk for Trisomy 18 does not change with maternal age, while the risk for Trisomy 21 increases significantly with maternal age.
- Trisomy 13 vs 18
- Trisomy vs Triploidy
- Monosomy vs Trisomy
- Down Syndrome vs Turner Syndrome
- Genetic Disorders vs Chromosomal Disorders
- Williams Syndrome vs Down Syndrome
- P53 vs P21
- Nullisomy vs Double Monosomy
- Mosaic Down Syndrome vs Down Syndrome
- Genetic vs Congenital Disorders
- Mendelian vs Chromosomal Disorders
- Monogenic Disorders vs Chromosomal Disorders
- Down Syndrome vs Klinefelter Syndrome
- Down Syndrome vs Edward Syndrome
- Mosaicism vs Uniparental Disomy
- XX vs XY Chromosomes
- Uniparental Disomy vs Genomic Imprinting
- Haploid vs Diploid
- Nondisjunction in Meiosis 1 vs 2