In-Depth Notes on Genetic Etiology and Schizophrenia

Genetic Etiology of Schizophrenia

• Complex and multifactorial in nature.

Odds Ratio (OR)

• An Odds Ratio is a statistical measure used to quantify the strength of the association between an exposure and an outcome.

• Definition: The OR indicates the odds of an outcome occurring with a specific exposure compared to the odds of the outcome in the absence of that exposure.

Family History as a Predictor

• Impact of Family History on Schizophrenia Risk:

  • Without family history: Risk of developing schizophrenia is approximately 1%.

  • With family history: Risk increases to about 9%.

Genetic Factors in Schizophrenia

• Schizophrenia is influenced by genetic predispositions but genetics alone are neither necessary nor sufficient for the disorder.

• Risk for developing schizophrenia varies by relationship:

  • General Population: 1%

  • First cousins: 2%

  • Uncles/Aunts: 2%

  • Nephews/Nieces: 4%

  • Grandchildren: 5%

  • Parents: 6%

  • Half siblings: 6%

  • Siblings: 9%

  • Children: 13%

  • Fraternal twins: 17%

  • Identical twins: 100%

Human Genome Overview

• The human genome includes:

  • 23 pairs of chromosomes (22 autosomes, 1 sex chromosome).

  • Approximately 6 billion nucleotides (~3 billion base pairs).

  • Approximately 4 million single nucleotide polymorphisms (SNPs); 96% of nucleotides are identical across humans.

  • Roughly 20,000 protein-coding genes, resulting in about 100,000 different proteins.

Basic Model of Genetic Variation

• Genetic Variation can manifest as:

  • Genes: SNPs or other variations.

  • Cells: Molecular abnormalities resulting from genetic variations.

  • Systems: Abnormal brain functions linked to schizophrenia.

  • Behavior: Emergent phenomena reflecting changes in behavior due to underlying biological factors.

Identification of Genetic Variants

• The efficacy of genetic association studies:

  • Example: Investigating SNP X for its association with schizophrenia.

  • Analysis involves comparing the prevalence of SNP carriers between schizophrenia patients and control subjects.

  • Statistical significance can be calculated using the Chi-squared test (e.g., $ ext{χ}^2 = 5.38; p = .023$).

The Polygenic Nature of Schizophrenia

• Schizophrenia is identified as a polygenic disorder through methods like Manhattan plots, which display the significance of SNPs across chromosomes.

• Dots above a certain threshold signify genetic variants associated with schizophrenia.

Types of Genetic Variations

• Atypical Variations include:

  • Deletions: Missing segments of chromosomes.

  • Duplications: Extra identical sections.

  • Insertions: Segments that are incorrectly located.

  • Can occur through inheritance or de novo processes.

Copy Number Variants (CNVs)

• CNVs are significant in schizophrenia and can either be losses or gains in specific chromosomal regions.

• Graphical representation via Manhattan plots illustrates the significance of various CNV gains/losses in association with schizophrenia.

Function of Associated Genes

• Genes related to schizophrenia are vital for cellular activities from conception through to adulthood, impacting:

  • Cellular functions and developments, especially in the brain.

  • Genes linked to schizophrenia predominantly affect brain cell development and maintenance.

Research Insights (Huckins et al, 2019)

• Analyzing genetic variants and their expression in the brain:

  • Regions of interest include specific brain areas and developmental periods where gene expression is critical for social, general, and emotional cognition.

  • Notable findings detail distinct developmental windows correlated with the identified genetic risks.

Conclusion

• Understanding the role of genetic factors is pivotal, but it is essential to recognize that environmental influences also play a significant role in determining the risk of developing schizophrenia.

• Future discussions will explore Environmental Risk Factors linked to schizophrenia.