[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Genetic disease](https://durgical.com/en/general-pathology/#a-genetic) › Trisomies 21, 18 and 13, and the 22q11.2 deletion [General pathology](https://durgical.com/en/general-pathology/) · [Genetic disease](https://durgical.com/en/general-pathology/#a-genetic) # Trisomies 21, 18 and 13, and the 22q11.2 deletion - Topic The three trisomies that reach birth and the commonest microdeletion have features typical enough to be recognised when the newborn is examined. Updated 2026-11-01 ## Key points - Down: the great majority from maternal nondisjunction; a minority from a Robertsonian translocation (recurrence risk) and very few from mosaicism. - Down: atrioventricular canal defect, duodenal atresia, Hirschsprung disease, acute leukaemias in childhood and early Alzheimer disease (APP gene on 21). - Edwards: clenched hands with overlapping fingers, rocker-bottom feet, micrognathia and a prominent occiput. - Patau: holoprosencephaly, cleft lip and palate, microphthalmia, polydactyly and scalp defects. - 22q11.2: conotruncal heart defects, thymic hypoplasia (T-cell deficit), cleft palate, hypocalcaemia from absent parathyroids and psychiatric risk. ## What it is Down syndrome (trisomy 21) is the commonest chromosome abnormality in live births and the commonest genetic cause of intellectual disability. Trisomies 18 (Edwards) and 13 (Patau) are much more severe and most affected infants die in the first year. The 22q11.2 deletion (DiGeorge or velocardiofacial syndrome) disturbs development of the third and fourth pharyngeal pouches. ## Key facts - Trisomy 21 raises the risk of acute lymphoblastic and myeloid leukaemia; newborns may have a transient myeloproliferative disorder. - In Down syndrome, hypothyroidism, atlantoaxial instability and hearing loss are common. - The 22q11.2 deletion is explained by faulty development of the third and fourth pharyngeal pouches and of the neural crest cells of the outflow tract. ## The syndromes compared | Syndrome | Cause | Key features | Heart | Outlook | | --- | --- | --- | --- | --- | | [Down syndrome](https://durgical.com/en/conditions/down-syndrome/) | Trisomy 21 | Hypotonia, upslanting palpebral fissures, flat facial profile, single palmar crease, intellectual disability | Atrioventricular canal, ASD, VSD | Survival into adulthood; early Alzheimer disease | | [Trisomies 18 and 13](https://durgical.com/en/conditions/trisomy-18-and-trisomy-13/) | Trisomy 18 (Edwards) or 13 (Patau) | 18: clenched fists, rocker-bottom feet; 13: holoprosencephaly, facial clefts, polydactyly | VSD and other complex defects | Most die in the first year | | [22q11.2 deletion](https://durgical.com/en/conditions/digeorge-syndrome/) | Microdeletion on 22 (includes TBX1), almost always new | Hypoplastic thymus and parathyroids, cleft palate, typical face, learning problems | Truncus arteriosus, tetralogy of Fallot, interrupted aortic arch | Variable; infections, hypocalcaemia and psychiatric disorders | ## In the lab - First-trimester screening in Down syndrome: increased nuchal translucency, low PAPP-A and high β-hCG. - Second-trimester quadruple screen in Down syndrome: low AFP and oestriol, high hCG and inhibin A; in trisomy 18, low AFP, oestriol and hCG. - The 22q11.2 deletion is confirmed by FISH or microarray; lymphocyte subsets show few T cells. ## Memory aid Twenty-one: a cross-shaped heart defect and a double-bubble gut; eighteen: a clenched fist; thirteen: a split face; twenty-two: no thymus, no calcium. ## Test yourself Think of the answer, then tap the question to see it. ## Which heart defect is characteristic of Down syndrome? The atrioventricular canal (endocardial cushion) defect. ## Why do people with Down syndrome develop Alzheimer disease early? Because the amyloid precursor protein (APP) gene lies on chromosome 21 and they carry an extra copy. ## Which laboratory finding does the absence of parathyroids explain in the 22q11.2 deletion? Hypocalcaemia with low PTH, which can cause tetany or seizures in the newborn. ## Which trisomy is associated with holoprosencephaly and polydactyly? Trisomy 13, or Patau syndrome. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/general-pathology/trisomies-21-18-and-13-and-the-22q11-2-deletion/) ## Related - [Chromosome abnormalities: number and structure](https://durgical.com/en/general-pathology/chromosome-abnormalities-number-and-structure/) - [Sex chromosome disorders: Klinefelter and Turner](https://durgical.com/en/general-pathology/sex-chromosome-disorders-klinefelter-and-turner/) - [Tumours of infancy and childhood](https://durgical.com/en/general-pathology/tumours-of-infancy-and-childhood/) ## Related conditions - [Down syndrome (trisomy 21)](https://durgical.com/en/conditions/down-syndrome/) - [Trisomy 18 (Edwards) and trisomy 13 (Patau)](https://durgical.com/en/conditions/trisomy-18-and-trisomy-13/) - [DiGeorge syndrome (22q11.2 deletion syndrome)](https://durgical.com/en/conditions/digeorge-syndrome/) - [Acute leukaemia (AML and ALL)](https://durgical.com/en/conditions/acute-leukaemia/) - [Hirschsprung disease](https://durgical.com/en/conditions/hirschsprung-disease/) - [Alzheimer disease](https://durgical.com/en/conditions/alzheimer-disease/) - [Congenital hypothyroidism](https://durgical.com/en/conditions/congenital-hypothyroidism/) - [Cleft lip and palate](https://durgical.com/en/conditions/cleft-lip-and-palate/) - [Tetralogy of Fallot](https://durgical.com/en/conditions/tetralogy-of-fallot/) - [Atrial septal defect](https://durgical.com/en/conditions/atrial-septal-defect/) - [Ventricular septal defect](https://durgical.com/en/conditions/ventricular-septal-defect/) - [Schizophrenia](https://durgical.com/en/conditions/schizophrenia/) ## Elsewhere in DurgiPedia - [Meiosis and nondisjunction: where trisomies come from](https://durgical.com/en/embryology/meiosis-and-nondisjunction-where-trisomies-come-from/) - [Prenatal diagnosis: ultrasound, serum screening, cell-free DNA, CVS, amniocentesis](https://durgical.com/en/embryology/prenatal-diagnosis-ultrasound-serum-screening-cell-free-dna-cvs-amniocentesis/) - [22q11.2 deletion (DiGeorge): the third and fourth pouches](https://durgical.com/en/embryology/22q11-2-deletion-the-third-and-fourth-pouches/) - [Pharyngeal pouches: tonsil, thymus, parathyroids and C cells](https://durgical.com/en/embryology/pharyngeal-pouches-tonsil-thymus-parathyroids-and-c-cells/) - [Atrioventricular septal defect (endocardial cushion defect)](https://durgical.com/en/embryology/atrioventricular-septal-defect/) - [Holoprosencephaly](https://durgical.com/en/embryology/holoprosencephaly/) - [Duodenal atresia and stenosis](https://durgical.com/en/embryology/duodenal-atresia-and-stenosis/) - [T-cell and combined deficiencies: DiGeorge, SCID, Wiskott–Aldrich, ataxia-telangiectasia](https://durgical.com/en/immunology/t-cell-and-combined-deficiencies-digeorge-scid-wiskott-aldrich-ataxia-telangiect/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Down syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/down-syndrome/) (MedlinePlus, US National Library of Medicine, 2026); [Trisomy 18: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/trisomy-18/) (MedlinePlus, US National Library of Medicine, 2026); [Trisomy 13: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/trisomy-13/) (MedlinePlus, US National Library of Medicine, 2026); [22q11.2 deletion syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/22q112-deletion-syndrome/) (MedlinePlus, US National Library of Medicine, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/trisomies-21-18-and-13-and-the-22q11-2-deletion/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/trisomies-21-18-and-13-and-the-22q11-2-deletion/