PE29.1-5 | Chromosomal Abnormalities — Graded Quiz

Correct. An unaffected sibling of a translocation Down syndrome patient has a 2/3 chance of being a balanced carrier. Early karyotyping allows informed reproductive counselling in adulthood.

For Robertsonian translocation Down syndrome: karyotype all first-degree relatives. An unaffected sibling has 2/3 probability of being a balanced carrier. Early counselling respects reproductive autonomy.

Unaffected siblings have a 2/3 chance of carrying the Robertsonian translocation. Karyotyping the daughter now allows timely counselling. Deferring until reproductive age is appropriate only if parents decline early testing.

Correct. The 'double bubble' sign confirms duodenal atresia requiring immediate surgical consultation. Echocardiography is simultaneously urgent because AVSD occurs in ~40–50% of Down syndrome neonates and must be identified before surgery.

Down syndrome associations: AVSD (40–50%), duodenal atresia (double bubble), hypothyroidism, ALL, atlantoaxial instability, Hirschsprung disease. Duodenal atresia + AVSD both require urgent attention at birth.

Both investigations are simultaneously urgent: duodenal atresia needs immediate surgical repair, and AVSD must be excluded before anaesthesia. Thyroid and haematology workup are not urgent on day 2.

Correct. Guidelines recommend starting low-dose estrogen at ~11–12 years chronological age to mimic the normal timing and tempo of puberty, even while continuing growth hormone. Delaying beyond 13–14 years harms bone density and psychological wellbeing.

Turner syndrome pubertal induction: low-dose estrogen at ~11–12 years (17-beta estradiol preferred), increasing over 2–3 years; cyclic progesterone added after 12–24 months. Growth hormone is continued concurrently until near-final height.

Estrogen should begin at ~11–12 years at low doses to mimic spontaneous puberty; progesterone is added 12–24 months later. Deferring for maximum height gain risks impaired bone mineralisation and psychosocial development.

Correct. The ISCN notation for classic Turner syndrome is 45,X — a single X chromosome with no second sex chromosome. '45,XO' is an outdated, incorrect notation; 'O' is not an ISCN symbol.

Always write Turner syndrome as 45,X — never 45,XO. ISCN uses 45 to indicate the total chromosome count (22 autosome pairs + 1 sex chromosome). Variants include 45,X/46,XX mosaicism and isochromosome Xq.

The correct ISCN notation is 45,X. The letter 'O' has no meaning in ISCN; writing '45,XO' is a common error. Turner syndrome has 45 total chromosomes (22 pairs autosomes + 1 sex chromosome).

Correct. Exogenous testosterone suppresses the hypothalamic–pituitary–gonadal axis, eliminating any residual spermatogenesis. TESE must be attempted before testosterone to preserve the option of biological fatherhood.

Klinefelter fertility sequence: TESE first (focal spermatogenesis present in ~50%) → sperm cryopreservation → then testosterone. This sequence preserves biological fatherhood options.

TESE first, testosterone after is the established sequence. Exogenous testosterone suppresses LH/FSH, eliminating any focal spermatogenesis. ~50% of men with Klinefelter who undergo TESE can achieve biological paternity via ICSI.

Correct. After a child with non-disjunction trisomy 21, the empirical recurrence risk in subsequent pregnancies is approximately 1% above the maternal age-related background risk. At age 28, background risk is ~1:1000; recurrence risk is therefore approximately 1% + 0.1% ≈ 1.1%.

Recurrence risks for Down syndrome: non-disjunction = age-related + ~1%; maternal Robertsonian carrier = ~10–15%; paternal Robertsonian carrier = ~5%. Always counsel on the mechanism-specific risk.

For non-disjunction trisomy 21, recurrence risk = age-related risk + ~1%. It does NOT follow Mendelian inheritance. This contrasts with Robertsonian translocation, where recurrence is 10–15%.

Correct. In Turner syndrome with bicuspid aortic valve, aortic root dilatation and coarctation carry the highest mortality risk. MRI of the thoracic aorta must be performed at diagnosis and repeated every 5–10 years (or sooner if anomalies found).

Turner syndrome cardiovascular surveillance: echo at diagnosis, aortic MRI at baseline, repeat imaging every 5–10 years (or every 5–7 years with aortic anomaly). Aortic dissection risk is life-long even without prior identified anomaly.

Aortic dissection is the leading cause of death in Turner syndrome. Bicuspid aortic valve + Turner syndrome = mandatory aortic root imaging (MRI/CT). This is more urgent than bone age or pelvic scan.

Correct. Non-disjunction trisomy 21 can occur at any maternal age. Advanced maternal age significantly increases the risk (from ~1:1500 at age 20 to ~1:30 at age 45), but the absolute majority of affected births are to women under 35 because younger women have far more pregnancies.

Most Down syndrome births occur to mothers under 35 due to higher birth rates in younger women, even though per-pregnancy risk increases sharply with age. All mothers have some baseline risk.

Advanced maternal age increases risk but does not mean young mothers cannot have trisomy 21 children. Because most births are to women under 35, they account for the majority of Down syndrome births in absolute numbers.

Correct. Testosterone replacement in Klinefelter syndrome produces virilisation (beard growth, muscle mass, libido, energy) but does NOT restore testicular size or spermatogenesis. Testes remain small due to fibrosis and seminiferous tubule sclerosis.

Testosterone in Klinefelter syndrome corrects the hypogonadism phenotype (virilisation, bone density, mood) but does not reverse gonadal dysgenesis. Testes remain small; FSH/LH stay elevated. Gynaecomastia warrants evaluation but usually does not fully resolve with testosterone.

Testosterone corrects hypogonadism symptoms but not the primary gonadal defect. Testes remain small because the pathology is intrinsic (Sertoli/Leydig cell loss + tubular fibrosis). FSH/LH remain elevated because the primary defect is testicular.

Correct. Atlantoaxial instability (AAI) in Down syndrome with atlanto-dens interval >4.5–5 mm warrants activity restriction from high-risk manoeuvres (gymnastics, contact sports, diving, wrestling). Spine specialist referral is needed. Non-high-risk activities like recreational swimming (without diving) are generally permitted.

Atlantoaxial instability in Down syndrome: screen with cervical X-ray in flexion/extension. Atlanto-dens interval >4.5–5 mm requires restriction from gymnastic and contact activities and spine specialist referral. Previously mandatory for Special Olympics; now individualised.

AAI in Down syndrome requires activity restriction from high-risk activities even in asymptomatic children, and a spine specialist opinion. Surgery is reserved for patients with neurological compromise.