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Summary
The sex ratio (SR) in Down syndrome (DS) typically shows more males, especially in trisomy 21 and translocation cases. However, mosaic Down syndrome exhibits a female predominance, and the SR has varied over time.
Area of Science:
- Genetics
- Human Biology
- Reproductive Health
Context:
- Down syndrome (DS) is a genetic disorder caused by trisomy 21.
- The sex ratio (SR) in DS, the proportion of males to females, can vary.
- Previous studies have reported differing SRs in various populations and DS subtypes.
Purpose:
- To analyze and synthesize data on the sex ratio in Down syndrome from 55 publications.
- To investigate factors influencing the sex ratio in DS, including cytogenetic type and temporal trends.
- To review potential genetic mechanisms underlying male predominance in trisomy 21.
Summary:
- A meta-analysis of 55 studies indicates a male predominance in Down syndrome (SR > 1) across most populations and DS types, including free trisomy 21 and translocations.
- An excess of females was observed in mosaic Down syndrome (SR = 0.83), while non-mosaic cases showed SR close to 1.3.
- The SR in Down syndrome has shown temporal variations, increasing from the 1940s to the 1980s and declining in the 1990s, potentially linked to diagnostic methods and paternal contribution.
Impact:
- Provides a comprehensive overview of sex ratio variations in Down syndrome.
- Highlights differences in SR across various cytogenetic forms of DS.
- Offers insights into potential genetic and temporal factors influencing DS sex ratios, contributing to a better understanding of its etiology.