| Downs (trisomy 21) | 21 | Short stature, simian crease, almond shaped eyes due to epicanthic folds, upslanting palpebral fissures, low set ears, brushfield spots, and poor muscle tone. Most have mild (IQ 50-70) to moderate (IQ 35-50) mental retardation |
| Angelman syndrome (Happy puppet syndrome) | 15q11 maternal origin | Flapping hand movements (uplifted, flexed arms when walking), ataxia, pronounced verbal delay (compared to comprehension), serveve to profound learning disability, seizures and sleep problems |
| Prader-Willi | 15q11 paternal origin | Hyperphagia, excessive weight gain, short stature, frequent skin picking, mild learning disability, small gonads, and hypotonia |
| Cri du chat | 5p deletion | Characteristic cry like a meowing kitten, hypotonia, hypertelorism, a down-turned mouth, and microcephaly |
| Velocardiofacial syndrome (Di George syndrome) | 22q (deletion) | Cleft palate, cardiac problems, and learning disabilities. A higher rate of psychiatric disorders is also seen |
| Edwards's syndrome (trisomy 18) | 18 | Kidney malformations, upturned nose, webbing of second and third toes, and clubbed feet (rocker bottom) |
| Lesch-Nyhan syndrome | Xq26-27 | Self mutilation, dystonia and writhing movements |
| Smith-Magenis syndrome | 17p11 | Pronounced self injurious behaviour, self hugging, and a hoarse voice |
| Fragile X | X | Elongated face, large ears, large testicles, hand flapping, shyness, and little eye contact |
| Wolf Hirschhorn syndrome | 4p | Profound mental retardation, microcephaly, seizures, down turned fishlike mouth, Greek warrior helmet face, and cleft lip |
| Patau syndrome (trisomy 13) | 13 | Mental retardation, polydactyl, microcephaly, overlapping of fingers over thumb |
| Rett syndrome | Xq28 | Normal for the first 12 months. Regression and loss of skills from around 18 months onwards. Hand-wringing movements are the most common feature. Associated learning disability is profound. Affects girls almost exclusively |
| Tuberous sclerosis | Genetically heterogeneous, linkage to 9q and 16p | Hamartomatous tumours affect various organs including the brain. 80% suffer with epilepsy. Autism, ADHD, and sleep problems are common |
| Williams syndrome | 7q11 deletion | Elfin like features, social disinhibition, and abnormal friendliness towards strangers. Very sensitive hearing is also seen. Advanced verbal skills, speech is articulate but superficial (referred to as cocktail party speech) |
| Rubinstein-Taybi syndrome | Unclear, 16p deletions have been reported | Tend to be short with small heads. Associated with a friendly disposition and moderate learning disability |
| Klinefelter syndrome | Extra X chromosome in phenotypic males (47 XXY) | Tend to be tall with small testicles. Typically introverted with poor social and school performance |
| Jacob's syndrome | Extra Y chromosome (47 XYY) | Tend to be tall. Sexual development is normal. Tend to have lower mean intelligence. Early links with criminality have not been supported |
| Coffin-Lowry syndrome | Xp22 | Short stature, slanting eyes with short broad nose. Severe learning difficulty |
| Turner syndrome | 45 X0 | Short stature, webbed neck, widely spaced nipples |
| Niemann Pick disease (types A and B) | 11p15 | Abdominal swelling, cherry red spot, feeding difficulties |
