| Feature | Down Syndrome | Turner Syndrome | Klinefelter Syndrome | Super Female |
|---|---|---|---|---|
| Karyotype | 47, +21 | 45, XO | 47, XXY | 47, XXX |
| Sex | Male or Female | Female only | Male only | Female only |
| Chromosome cause | Extra autosome (Chr. 21) | Missing sex chromosome (X) | Extra sex chromosome (X in male) | Extra X in female |
| Total chromosomes | 47 | 45 | 47 | 47 |
| Barr bodies | 0 (male) or 1 (female) | 0 | 1 | 2 |
| Fertility | Usually infertile | Infertile (streak gonads) | Reduced fertility | Often fertile |
| Height | Short | Short | Tall | Normal |
| Key features | Intellectual disability, epicanthic folds, simian crease, broad palms | Webbed neck, shield chest, primary amenorrhoea | Gynaecomastia, small testes, sparse body hair | Often phenotypically normal; may have mild effects |
| Cause | Non-disjunction (meiosis, usually maternal) | Non-disjunction | Non-disjunction | Non-disjunction |
| Age effect | Increases with maternal age | No clear age effect | No clear age effect | No clear age effect |
| Intelligence | Intellectual disability | Usually normal | May have mild issues | Usually normal |
NEET Traps
- Turner = XO but FEMALE (no Y = female by default)
- Klinefelter = XXY but MALE (Y present = SRY = male)
- Down syndrome is the ONLY autosomal (non-sex chromosome) disorder in this list
- Super Female is often NORMAL despite an extra X (unlike other aneuploidies)