Pediatrics
Chromosomal Abnormalities
Paediatric chromosomal disorders for NEET-PG: Down, Turner and Klinefelter syndromes with karyotypes and surveillance, mapped to NMC PE32 codes.
MedNext Academy | 3 min read
Chromosomal Abnormalities
Paediatric chromosomal disorders for NEET-PG: Down, Turner and Klinefelter syndromes with karyotypes and surveillance, mapped to NMC PE32 codes.
This chapter covers the common paediatric chromosomal disorders: Down syndrome, Turner syndrome and Klinefelter syndrome, with their genetics, karyotype notation, clinical recognition, complication surveillance and parental counselling, alongside the role of newborn screening. It stresses coordinated care and cardiovascular vigilance.
High-yield: Chromosomal Abnormalities
- Down syndrome is a diagnosis of a child, not a karyotype alone, so the first response combines confirmation, congenital heart evaluation, thyroid, hearing and vision surveillance and counselling.
- A normal karyotype is 46,XX or 46,XY, and trisomy 21 is written 47,XX,+21 or 47,XY,+21, showing chromosome count, sex chromosome complement and the extra chromosome.
- In suspected Down syndrome, absence of a murmur does not exclude congenital heart disease, and bilious vomiting, cyanosis or feeding failure needs urgent evaluation.
- Do not quote recurrence risk in Down syndrome until the cytogenetic subtype is known, because translocation results can require parental karyotyping and genetics referral.
- Down syndrome care fails when each complication is handled in isolation, so the paediatrician coordinates growth, development, hearing, school function and caregiver goals together.
- Turner syndrome should be considered in any girl with unexplained short stature even when the classic webbed neck or shield chest is absent.
- The classic Turner karyotype is 45,X, but mosaic and structural X abnormalities are common enough that a normal-looking short girl still deserves cytogenetic testing.
- Turner syndrome is a lifelong surveillance diagnosis in which the cardiovascular plan is as important as growth treatment, because aortic disease can be silent.
- Syncope, chest pain, hypertension or known aortic dilatation in Turner syndrome needs urgent cardiovascular assessment, since aortic complications can be catastrophic.
- Pregnancy counselling in Turner syndrome is unsafe without cardiovascular risk assessment, because aortic disease can make pregnancy life-threatening.
- Klinefelter syndrome is usually 47,XXY and may not be obvious before puberty, with the clue being a tall boy with small firm testes, pubertal delay, gynaecomastia or learning difficulty.
- Klinefelter syndrome is frequently missed because infants usually do not look dysmorphic, and the clinical window opens with language delay and school difficulty.
- Newborn screening is a distinct public-health tool that detects treatable biochemical risk before symptoms rather than every genetic disorder.
- A positive newborn screen for a time-critical disorder must be recalled and confirmed urgently, because waiting for symptoms can allow preventable neurodevelopmental injury.
- Counselling parents after a chromosomal diagnosis is a clinical skill that should be truthful, kind, private, staged and linked to the child in front of the family.
Karyotype notation
- **Normal karyotype:** 46,XX or 46,XY.
- **Trisomy 21 (Down syndrome):** 47,XX,+21 or 47,XY,+21.
- **Turner syndrome:** Classic 45,X, but mosaic and structural X abnormalities are common.
- **Klinefelter syndrome:** Typically 47,XXY, often not obvious before puberty.
NMC competencies in this chapter
- **PE32.1:** Down Syndrome: Genetic Basis, Risk, Prenatal Diagnosis and Management
- **PE32.3:** Normal Karyotype, Trisomy 21 and Other Autosomal Trisomies
- **PE32.6:** Turner Syndrome: Genetics, Complications and Management
- **PE32.8:** Normal and Turner Karyotype Interpretation
- **PE32.11:** Klinefelter Syndrome and Core Single-Gene Genetics
Frequently Asked Questions
How is trisomy 21 written in karyotype notation?
It is written 47,XX,+21 or 47,XY,+21, compared with the normal 46,XX or 46,XY. The notation gives the total chromosome count, the sex chromosome complement and the extra chromosome.
When should Turner syndrome be considered?
In any girl with unexplained short stature, even without the classic webbed neck or shield chest. The classic karyotype is 45,X, but mosaic and structural X abnormalities are common, so cytogenetic testing is still warranted.
Why is cardiovascular assessment central in Turner syndrome?
Turner syndrome is a lifelong surveillance diagnosis in which aortic disease can be silent. Syncope, chest pain, hypertension or aortic dilatation needs urgent cardiac assessment, and pregnancy counselling is unsafe without cardiovascular risk assessment.
Why is Klinefelter syndrome often missed?
Infants with Klinefelter syndrome usually do not look dysmorphic, so it is frequently missed early. The clinical window opens with language delay, school difficulty, tall stature, small firm testes and incomplete virilisation around puberty.
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