Turner and Klinefelter Syndromes — 2014 Paper I

Approach

• Demand of Question: Describe the chromosomal basis, major clinical features and reproductive consequences of Turner and Klinefelter syndromes.
• Structuring the Response: Explain each syndrome separately and conclude with a brief comparison.
• Key Dimensions to Cover: 45,X, 47,XXY, nondisjunction, gonadal dysgenesis, infertility, secondary sexual characteristics and karyotype.

Model Answer

Introduction: Turner and Klinefelter syndromes are numerical abnormalities of the sex chromosomes, usually arising from meiotic nondisjunction.

Turner Syndrome

Turner syndrome usually results from monosomy of the X chromosome.

Karyotype: 45,X

It occurs in phenotypic females.

Major features

• short stature;
• webbed neck in some cases;
• broad chest;
• ovarian dysgenesis;
• poorly developed secondary sexual characteristics;
• primary amenorrhoea;
• infertility.

Because ovarian development is impaired, estrogen levels are generally low.

Some individuals show mosaic forms such as:

45,X / 46,XX

which may produce milder manifestations.

Klinefelter Syndrome

Klinefelter syndrome results from the presence of an additional X chromosome in a phenotypic male.

Karyotype: 47,XXY

Major features

• tall stature;
• long limbs;
• small testes;
• reduced testosterone production;
• sparse facial/body hair;
• gynecomastia in some individuals;
• infertility, often due to impaired spermatogenesis.

Mosaic forms such as:

46,XY / 47,XXY

may also occur.

Comparison

Conclusion

Turner and Klinefelter syndromes demonstrate how abnormalities in sex chromosome number can influence growth, gonadal development and reproduction. Cytogenetic diagnosis is important for clinical management and genetic counselling.