Q.Differentiate between Turner's syndrome and Down's syndrome.
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Start your 14-day free trial to unlock the full solution →Turner's syndrome and Down's syndrome are both chromosomal disorders, but they differ in cause (sex chromosome monosomy vs. autosomal trisomy), sex affected (only females vs. both sexes), and key features (short stature, webbed neck vs. intellectual disability, characteristic facial features).
The Core Concept: Chromosomal Number and Type
Both Turner's syndrome and Down's syndrome arise from errors in chromosome number during cell division (meiosis). The critical difference lies in which chromosome is affected and how its number changes.
Turner's syndrome is a sex chromosome aneuploidy — specifically, a monosomy of the X chromosome (45,X). This means a female has only one X chromosome instead of two. Because the Y chromosome is absent, the individual develops as female, but the missing genetic material from the second X leads to specific physical and developmental features.
Down's syndrome is an autosomal aneuploidy — specifically, a trisomy of chromosome 21 (47,+21). This means an extra copy of chromosome 21 is present. Since chromosome 21 is an autosome (not a sex chromosome), this condition affects both males and females equally and produces a distinct set of features, most notably intellectual disability.
A common mistake is to think Turner's syndrome is a "female version" of Down's syndrome. They are fundamentally different: Turner's involves a missing sex chromosome, while Down's involves an extra autosome. They affect different chromosomes and have almost no overlapping features.
Step-by-Step Comparison
Let's break down the differences systematically.
1. Chromosomal Basis
- Turner's syndrome: The karyotype is 45,X (or 45,X0). The individual has 45 total chromosomes — one X chromosome is missing. This is a monosomy.
- Down's syndrome: The karyotype is 47,+21. The individual has 47 total chromosomes — an extra copy of chromosome 21. This is a trisomy.
2. Sex Affected
- Turner's syndrome: Only females are affected. The absence of a Y chromosome means the individual develops as female.
- Down's syndrome: Both males and females can be affected equally, since chromosome 21 is an autosome.
3. Cause of the Error
- Turner's syndrome: Usually caused by nondisjunction during gamete formation in either parent, leading to a sperm or egg missing a sex chromosome. In about 80% of cases, the missing X is from the father's sperm.
- Down's syndrome: Most commonly caused by nondisjunction of chromosome 21 during meiosis in the mother (especially with increasing maternal age). Less commonly, it can result from a Robertsonian translocation.
4. Key Physical Features
- Turner's syndrome:
- Short stature (most consistent feature)
- Webbed neck (excess skin folds)
- Low hairline at the back of the neck
- Broad chest with widely spaced nipples
- Lymphedema (swelling) of hands and feet at birth
- Ovarian dysgenesis (streak gonads) → infertility and lack of secondary sexual characteristics
- Down's syndrome:
- Intellectual disability (mild to moderate)
- Flat facial profile, upward-slanting eyes (epicanthal folds)
- Single palmar crease (simian crease)
- Protruding tongue
- Short, broad hands
- Congenital heart defects (common)
- Increased risk of leukemia and Alzheimer's disease
5. Intelligence and Development
- Turner's syndrome: Intelligence is usually normal, though some individuals may have specific learning difficulties (e.g., with spatial reasoning, mathematics). Verbal skills are typically strong.
- Down's syndrome: Intellectual disability is a hallmark feature. IQ ranges from mild to moderate impairment. Language development is delayed.
6. Fertility …
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