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Common chromosomal syndromes
Each chromosomal syndrome is recognised by a combination of appearance, a typical heart defect and associated problems — Down syndrome with AVSD and duodenal atresia, Turner with short stature and coarctation, 22q11 with a conotruncal defect and hypocalcaemia — and the first test in a child with intellectual disability and malformations is chromosomal microarray (CMA).
Why it matters in the exam
In Down syndrome the exam asks about the mechanism (95% non-disjunction linked to maternal age, about 4% Robertsonian translocation, which needs parental karyotypes because of recurrence risk, 1% mosaicism), the associated malformations — atrioventricular septal defect (AVSD), duodenal atresia with a "double bubble" and Hirschsprung disease — and follow-up: echocardiography for every newborn, thyroid tests at birth, 6 and 12 months and then yearly, hearing and vision checks, and attention to leukaemia, coeliac disease, sleep apnoea and atlanto-axial instability.
Turner syndrome (45,X) appears in a newborn girl with lymphoedema of the hands and feet or in an adolescent with short stature and absent puberty; associations are coarctation and a bicuspid aortic valve, horseshoe kidney and ovarian insufficiency. Every girl with unexplained short stature needs a karyotype. Treatment: growth hormone and later oestrogen. Klinefelter syndrome (47,XXY) appears in a tall adolescent with small firm testes, gynaecomastia and infertility. 22q11.2 deletion (DiGeorge): tetralogy of Fallot or interrupted aortic arch, hypocalcaemia from hypoparathyroidism, T-cell deficiency, cleft palate and later psychiatric disorders.
Trisomy 18 (Edwards) — clenched fists with overlapping fingers, rocker-bottom feet, intrauterine growth restriction and heart defects; trisomy 13 (Patau) — holoprosencephaly, cleft lip and palate, polydactyly and a scalp defect. Fragile X is the leading heritable cause of intellectual disability in boys (long face, large ears, large testes after puberty, autism). Williams syndrome — supravalvular aortic stenosis, hypercalcaemia and a very sociable personality.
Key points
- Down: AVSD, duodenal atresia, hypothyroidism, leukaemia.
- Translocation in Down syndrome → parental karyotypes.
- Turner: short stature, coarctation, ovarian insufficiency.
- 22q11.2: conotruncal defect, hypocalcaemia, T-cell deficiency.
- Chromosomal microarray is the first test for intellectual disability and malformations.
Summary table
| Syndrome | Clues | Heart and malformations | Follow-up or test |
|---|---|---|---|
| Down (trisomy 21) | Hypotonia, flat facial profile, single palmar crease, sandal gap | AVSD, duodenal atresia, Hirschsprung | Echo at birth, thyroid at birth, 6 and 12 months then yearly; hearing, vision, coeliac, leukaemia |
| Turner (45,X) | Short stature, webbed neck, lymphoedema of hands and feet in the newborn | Coarctation, bicuspid aortic valve, horseshoe kidney | Karyotype; growth hormone and oestrogen |
| Klinefelter (47,XXY) | Tall, small firm testes, gynaecomastia | — | High FSH and LH; testosterone |
| 22q11.2 (DiGeorge) | Hypocalcaemia, infections, cleft palate | Tetralogy of Fallot, interrupted arch, truncus | FISH or microarray; calcium and T cells |
| Edwards (trisomy 18) | Clenched fists, overlapping fingers, rocker-bottom feet, IUGR | Heart defects | Short survival in most cases |
| Patau (trisomy 13) | Holoprosencephaly, cleft, polydactyly, scalp defect | Heart defects | Short survival in most cases |
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Sources
- AAP Clinical Report: Health Supervision for Children and Adolescents With Down Syndrome, 2022 — Associated conditions and screening schedule
- International Turner Syndrome Consensus Group: Clinical practice guidelines for the care of girls and women with Turner syndrome, 2024 — Diagnosis and management
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Abnormalities of Chromosome Number and Structure
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.