Table 1.
Phenotypic characteristics of Down syndrome
| Characteristic | Frequency (%) | Reference |
|---|---|---|
| Craniofacial | ∼100 | 10, 114, 194, 195 |
| Epicanthal folds | ||
| Upward slanting palpebral fissures | ||
| Flat nasal bridge | ||
| Small brachycephalic head | ||
| Small ears | ||
| Small mouth | ||
| Other musculoskeletal abnormalities | ∼100 | 10, 196 |
| Hypotonia | ||
| Single transverse palmar crease | ||
| Clinodactyly with wide spacing | ||
| Cognitive impairment | ∼100 | 10, 17, 197 |
| Reduced brain volume | ||
| Learning and memory defects | ||
| Dementia | 40–50, increases with age | 12, 13, 14, 15, 16, 17, 18, 198, 199 |
| Visual | 18–60, increase with age | 10, 18 |
| Hearing | 18–80, increase with age | 10, 18 |
| Thyroid disease | 1–54, increase with age | 10, 18, 196, 200, 201 |
| Cardiac defects | 40–50 | 202, 203, 204 |
| ASD (45%) | ||
| VSD (35%) | ||
| Isolated secundum (8%) | ||
| Isolated PDA (7%) | ||
| Isolated Fallot's (4%) | ||
| Other | ||
| Gastrointestinal defects | 12 | 10 |
| Benign hematological abnormalities | ∼100 | 11 |
| Neonatal thrombocytopenia | ||
| Neonatal polycythemia | ||
| Neonatal neutrophilia, blast cells | ||
| Macrocytosis | ||
| Preleukemia and leukemia | ||
| TAM and silent TAM | 30 | 11, 53 |
| Acute myeloid leukemia | 1 | 53 |
| Acute lymphoblastic leukemia | 1 | 53 |
| Non-hematologic cancers | 50% of risk of individuals without DS | 18, 53, 56, 58, 59 |