Lecture Notes: Understanding Disease

Overview

• Exploration of the concepts of patient and disease.
• Disease classifications based on evolutionary and mechanistic causation.
• Disease is not merely infectious, chronic, or degenerative but has nuanced structures.
• Seven categories of disease help analyze defenses, maintenance, and vulnerability.

Key Concepts

Disease Risk

• Risk varies with genotype and environment.
• Graph structure:
  • X-axis: Genotypes
  • Y-axis: Disease risk (low to high)
• Environment D: Higher risk for most genotypes.
• Environment A: Risk for select genotypes above a certain threshold.

Categories of Disease

1. Genetic Causes

   • Diseases caused by single-gene mutations.
   • Examples: Trisomy 21, Cystic Fibrosis.
   • Often lethal/prevent reproduction; prevalence rising due to medical advancements.

2. Environmental Causes

   • Contribute to extrinsic mortality leading to natural selection.
   • Include infections, malnutrition, dehydration, etc.
   • Technology reduces prevalence, influences Category 3 diseases.

3. Byproducts of Defense Systems

   • Result from cost, deficiency, or misfunction of defense systems.
   • Increased prevalence as environmental diseases decline.
   • Include autoimmune diseases, anxiety disorders.

4. Diseases of Homeostasis

   • Affect systems designed to be adjustable.
   • Includes obesity, diabetes, addiction.
   • Result from environmental mismatches.

5. Diseases of Maintenance

   • Occur due to lack of Maintenance, especially with aging.
   • Affect brain structures, processes, and are not curable naturally.
   • Examples: Alzheimer's, arthritis.

6. Stochastic Developmental Problems

   • Rare, costly for evolution to fix.
   • Include premature delivery, SIDS.
   • Often filtered by quality control mechanisms.

7. Diseases of Pregnancy & Early Development

   • Result from equilibrium disruptions in relative conflicts.
   • Include preeclampsia, gestational diabetes.
   • May be linked to mental disorders.

Perspectives on Disease

• Patient's View: State of not feeling well.
• Physician's View: Abnormal conditions that produce symptoms.
• Pathogen's View: Symptoms aid in reproduction/transmission.
• Host's View: Byproducts of past selection or current defense mechanisms.

Disease Explanation

• Requires both mechanistic and evolutionary perspectives.
• Example: Crohn's disease explained through genetics and evolutionary mismatch.

Genetic and Environmental Causes

• Genetic causes: Defects (e.g., cystic fibrosis) and predispositions.
• Environmental causes: Catastrophic (e.g., infections) and accumulative (e.g., smoking).

Gene-Environment Interactions

• Diseases often result from gene-environment interactions.
• Smoking and barbecued meat as examples of environmental factors interacting with genetic predispositions in cancer.
• Importance of understanding interactions for disease risk assessment.

Summary

• Diseases categorized into seven evolutionary and mechanistic types.
• Genetic and environmental causes have distinct pathways.
• Many diseases result from gene-environment interactions.
• Depending on causation, organisms evolve defenses and maintenance mechanisms, though not always effectively.