Regarding the chromosomal abnormalities in aneuploidy, which of the following statements is NOT correct?

Explanation

## Aneuploidies: Comparative Clinical Features and Prognosis ### Turner Syndrome Cardiac Involvement **Key Point:** Turner syndrome (45,X) is **NOT** associated with uncommon cardiac defects. Rather, **cardiac abnormalities are a major and frequent concern** in Turner syndrome, including bicuspid aortic valve, aortic stenosis, coarctation of the aorta, and hypoplastic left heart syndrome. ### Comparative Table of Common Aneuploidies | Condition | Karyotype | Key Features | Prognosis | |---|---|---|---| | **Down Syndrome** | 47,XX,+21 or 47,XY,+21 | Intellectual disability (mild–moderate), AVSD, short stature, hypotonia | Best prognosis; many survive to adulthood | | **Edwards Syndrome** | 47,XX,+18 or 47,XY,+18 | Severe intellectual disability, rocker-bottom feet, clenched fists, cardiac defects | Poor; <5% survive beyond 1 year | | **Patau Syndrome** | 47,XX,+13 or 47,XY,+13 | Holoprosencephaly, polydactyly, cleft palate, cardiac defects, CNS malformations | Very poor; most die within weeks | | **Turner Syndrome** | 45,X (or mosaics) | Short stature, webbed neck, ovarian dysgenesis, **cardiac defects (bicuspid aortic valve, CoA)** | Good with hormone replacement; cardiac monitoring essential | **High-Yield:** Turner syndrome requires **cardiac screening** (echocardiography) and **renal ultrasound** as part of standard management. Aortic dissection is a life-threatening complication if cardiac defects are unrecognized. ### Why Each Autosomal Trisomy Has Different Outcomes ```mermaid flowchart TD A[Autosomal Trisomy]:::outcome --> B{Which chromosome?}:::decision B -->|Chromosome 21| C[Down Syndrome]:::outcome B -->|Chromosome 18| D[Edwards Syndrome]:::outcome B -->|Chromosome 13| E[Patau Syndrome]:::outcome C --> F[Mild-moderate disability<br/>Cardiac defects<br/>Long-term survival possible]:::action D --> G[Severe disability<br/>Multiple organ involvement<br/>Rare survival beyond 1 year]:::urgent E --> H[Severe CNS malformations<br/>Holoprosencephaly<br/>Most die within weeks]:::urgent ``` **Clinical Pearl:** Down syndrome (Trisomy 21) is the most common viable autosomal trisomy because chromosome 21 is the smallest autosome and contains the fewest genes. Trisomies 13 and 18 involve larger chromosomes with more genes, leading to more severe phenotypes and poor survival. ### Turner Syndrome: Why Cardiac Screening Matters **Mnemonic for Turner Syndrome Complications: SHORT OVARY** - **S**hort stature - **H**eart defects (bicuspid aortic valve, CoA) - **O**varian dysgenesis - **R**enal abnormalities - **T**hyroxine supplementation (hypothyroidism) - **O**titis media (hearing loss) - **V**ebbed neck - **A**ortic dissection risk - **R**ib abnormalities - **Y**ellow nails [cite:Robbins 10e Ch 5; Park 26e Ch 9]