Human Genetics, Disease Genomics, and Precision Medicine
Genetics at the interface of mechanism and medicine
Rare and common disease architecture
Monogenic disorders often arise from rare high-impact variants, whereas common diseases typically reflect many small-effect variants plus environment and development. Many real disorders occupy the continuum between these poles.
Clinical genetics vocabulary
Cancer as a somatic evolutionary process
Cancer genomes accumulate somatic mutations, copy-number changes, rearrangements, and epigenetic alterations under selective pressure within tissues. Tumor heterogeneity, clonal evolution, and microenvironmental selection make cancer genetics a dynamic evolutionary problem.
Clinical caution
Genetic associations are not diagnostic by themselves. Pathogenicity assessment requires inheritance pattern, population frequency, functional evidence, segregation, and clinical context.
Germline versus somatic variation
Germline
- Present in essentially all cells
- Can be inherited by offspring
- Important for constitutional disease and predisposition
Somatic
- Arises after fertilization in specific lineages
- Not generally inherited
- Central to cancer, mosaicism, and aging
What is the main advantage of germline testing in a family with inherited disease?
Germline testing can inform recurrence risk and familial cascade testing.
Correct answer: It can identify inherited risk across relatives
Why can the same pathogenic variant have different clinical severity in different individuals?
Phenotypic expressivity is shaped by multiple layers beyond the primary variant.
Correct answer: Because of modifiers such as background genetics, environment, age, sex, stochastic effects, and epigenetic or developmental context.
Interpreting a clinical variant
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1
Check whether the variant fits the inheritance pattern and phenotype.
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2
Assess population frequency and segregation in the family.
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3
Review functional evidence, computational predictions, and conservation.
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4
Integrate molecular data with the clinical presentation before classifying pathogenicity.
Which best describes a variant of uncertain significance?
A VUS lacks sufficient evidence for definitive classification at the time of interpretation.
Correct answer: A variant whose clinical effect is not yet established