Which Disease Is Not Hereditary? Understanding Acquired Conditions

My aunt, a vibrant woman in her early sixties, always attributed her occasional aches and pains to "just getting older." She’d dismiss any lingering cough or unusual fatigue with a wave of her hand, saying, "It's not like it runs in the family." This sentiment, while understandable, highlights a common misconception about diseases: the idea that all health issues are either inherited or entirely random. However, the reality is far more nuanced. Many diseases are, in fact, *not* hereditary, stemming from a complex interplay of environmental factors, lifestyle choices, and random cellular events. Understanding which diseases fall into this category is crucial for proactive health management and for dispelling the myth that our genetic destiny is the sole determinant of our well-being.

So, to directly answer the question: Many diseases are not hereditary. These are broadly categorized as acquired diseases, meaning they develop during a person's lifetime due to factors other than inherited genetic predispositions. These can include infections, injuries, lifestyle-related illnesses, and age-related conditions that aren't directly passed down through genes. It's important to distinguish these from genetic disorders, which are caused by mutations in an individual's DNA passed from parents to offspring.

The concept of heredity often conjures images of specific conditions like cystic fibrosis or Huntington's disease – ailments where the genetic link is undeniably strong. However, a vast majority of illnesses, affecting millions worldwide, do not fit this hereditary mold. My own journey through understanding my grandmother's battle with Alzheimer's, while having a complex genetic component, also made me intensely curious about conditions that are unequivocally *not* inherited. It’s a vital distinction, one that empowers individuals to take control of their health by focusing on modifiable risks.

The Spectrum of Disease: Hereditary vs. Acquired

Before delving into specific examples of non-hereditary diseases, it's essential to grasp the fundamental difference between hereditary and acquired conditions. Hereditary diseases, often referred to as genetic disorders, are caused by abnormalities in an individual's genes or chromosomes. These abnormalities are present from conception and can be passed down from parents to their children. Examples include sickle cell anemia, hemophilia, and Down syndrome. In these cases, the genetic blueprint itself carries the faulty instructions.

Acquired diseases, on the other hand, develop after birth. They are not present in the DNA inherited from parents. Instead, they arise from a multitude of external and internal factors that influence the body's functioning over time. These factors can include:

Infectious agents: Bacteria, viruses, fungi, and parasites can invade the body and cause illness.
Environmental exposures: Toxins, pollutants, radiation, and certain chemicals can damage cells and lead to disease.
Lifestyle choices: Diet, physical activity levels, smoking, alcohol consumption, and stress management play significant roles.
Injuries and trauma: Physical damage to the body can result in a range of health problems.
Age-related changes: While aging itself is a natural process, some conditions become more prevalent with age due to cumulative damage and wear-and-tear.
Autoimmune responses: In some cases, the body's own immune system mistakenly attacks healthy tissues.

It’s important to note that the line between hereditary and acquired can sometimes blur. For instance, some individuals may have a genetic *predisposition* to a certain disease, meaning they are more susceptible if exposed to certain triggers. However, the disease itself may only manifest due to acquired factors. Think of it like having a genetic "tendency" rather than a guaranteed inheritance of the full condition.

Common Diseases That Are Not Hereditary

The sheer volume of non-hereditary diseases is staggering. Let’s explore some prominent categories and specific examples that most people will encounter or be concerned about at some point in their lives. This isn't an exhaustive list, but it covers a significant breadth of common ailments.

Infectious Diseases: The Most Obvious Non-Hereditary Examples

Perhaps the most straightforward category of diseases that are not hereditary are infectious diseases. These are caused by pathogenic microorganisms like bacteria, viruses, fungi, or parasites. You don't inherit the common cold; you catch it from someone who has it. The same applies to a vast array of other illnesses.

Examples include:

Common Cold and Influenza (Flu): Caused by various viruses (rhinoviruses, coronaviruses for the cold; influenza viruses for the flu). Transmission occurs through respiratory droplets.
Bacterial Infections: Strep throat (Streptococcus pyogenes), urinary tract infections (often E. coli), pneumonia (various bacteria), tuberculosis (Mycobacterium tuberculosis).
Viral Infections: Chickenpox (varicella-zoster virus), measles (measles virus), COVID-19 (SARS-CoV-2 virus), HIV/AIDS (human immunodeficiency virus).
Parasitic Infections: Malaria (Plasmodium parasites), Giardiasis (Giardia lamblia).
Fungal Infections: Athlete's foot (tinea pedis), ringworm (tinea corporis), yeast infections (Candida albicans).

The key takeaway here is transmission. While some individuals might have a weaker immune system due to underlying, potentially hereditary conditions, the infectious agent itself is acquired from an external source. A healthy person can contract these diseases if exposed to the pathogen.

Traumatic Injuries and Their Aftermath

Physical trauma, by its very nature, is an external event. Fractures, sprains, concussions, and deep lacerations are not coded into our DNA at conception. They are the direct result of accidents, falls, sports injuries, or acts of violence.

Examples include:

Broken Bones (Fractures): Resulting from falls, impacts, or excessive force.
Sprains and Strains: Overstretching or tearing of ligaments and muscles.
Concussions and Traumatic Brain Injuries (TBIs): Caused by blows to the head or violent shaking.
Burns: From heat, chemicals, or electricity.
Dislocations: When bones are forced out of their normal joint position.

While certain genetic factors might influence bone density or tissue resilience, making someone *more susceptible* to injury in a given situation, the injury itself is not inherited. The healing process and potential long-term complications, however, can be influenced by genetics and overall health.

Diseases Linked to Lifestyle and Environment

This is perhaps the largest and most complex category of non-hereditary diseases. Our daily habits and the environments we inhabit profoundly impact our health. These conditions often develop gradually over years, accumulating the effects of our choices and exposures.

Cardiovascular Diseases (Beyond some rare genetic forms)

While some rare forms of heart disease have a strong genetic component (e.g., hypertrophic cardiomyopathy), the vast majority of common cardiovascular issues are considered acquired, driven by lifestyle and environmental factors. These are illnesses I've seen hit close to home, often among individuals whose families didn't have a history of severe heart problems, but who lived stressful lives with poor diets.

Examples include:

Atherosclerosis: The buildup of plaque in the arteries, largely influenced by diet high in saturated fats, lack of exercise, smoking, and high blood pressure.
Hypertension (High Blood Pressure): While genetics can play a role in susceptibility, factors like diet (high sodium), obesity, lack of physical activity, stress, and alcohol intake are major contributors.
Coronary Artery Disease (CAD): Often a consequence of atherosclerosis, leading to heart attacks.
Stroke: Frequently caused by blockages or ruptures in blood vessels supplying the brain, linked to the same risk factors as CAD.
Heart Failure: While some congenital heart defects are hereditary, many cases develop over time due to damage from CAD, hypertension, or other acquired conditions.

The Centers for Disease Control and Prevention (CDC) consistently highlights that heart disease is the leading cause of death in the United States, and a significant portion of this burden is attributable to modifiable risk factors. This underscores the powerful influence of acquired elements.

Type 2 Diabetes Mellitus

Type 1 diabetes is an autoimmune disease with some genetic links, but Type 2 diabetes, which accounts for about 90-95% of all diabetes cases, is largely acquired. It’s characterized by insulin resistance and the pancreas not producing enough insulin to meet the body's needs. This often develops due to a combination of factors.

Key contributing factors include:

Obesity and Overweight: Excess body fat, particularly around the abdomen, is a primary driver of insulin resistance.
Sedentary Lifestyle: Lack of regular physical activity reduces the body's sensitivity to insulin.
Unhealthy Diet: Diets high in processed foods, sugary drinks, and unhealthy fats contribute to weight gain and metabolic dysfunction.
Age: The risk increases with age, as metabolic processes can slow down.
Certain Ethnicities: While not strictly hereditary in the same way as single-gene disorders, certain ethnic groups have a higher prevalence, often linked to socioeconomic factors and dietary patterns that have become prevalent.

It's crucial to understand that while genetics might make someone *more prone* to developing Type 2 diabetes if exposed to these lifestyle factors, the disease itself is not directly inherited. My neighbor’s story exemplifies this; he was diagnosed with Type 2 diabetes in his late 40s after years of long work hours, quick meals, and minimal exercise, despite his parents being relatively healthy.

Certain Cancers

The relationship between genetics and cancer is complex. While some cancers are directly linked to inherited gene mutations (e.g., BRCA mutations for breast and ovarian cancer, Lynch syndrome for colorectal cancer), the vast majority of cancers are sporadic, meaning they arise from acquired genetic mutations that occur during a person's lifetime due to environmental exposures, lifestyle choices, and random cellular errors.

Examples of cancers that are predominantly acquired include:

Lung Cancer: Overwhelmingly linked to smoking (both active and passive exposure), though air pollution and radon exposure are also factors.
Skin Cancer (Melanoma, Basal Cell Carcinoma, Squamous Cell Carcinoma): Primarily caused by exposure to ultraviolet (UV) radiation from the sun or tanning beds.
Colorectal Cancer (Sporadic form): While Lynch syndrome and familial adenomatous polyposis (FAP) are hereditary, most cases are sporadic, influenced by diet, obesity, lack of exercise, and inflammatory bowel disease.
Stomach Cancer: Associated with Helicobacter pylori infection, diet (smoked and salted foods), and environmental factors.
Liver Cancer: Often linked to chronic viral hepatitis (Hepatitis B and C infections), alcohol abuse, and non-alcoholic fatty liver disease.

It’s vital to differentiate. If you have a strong family history of a specific cancer, especially if diagnosed at a young age, genetic testing might be recommended to identify inherited predispositions. However, for the majority of cancer diagnoses, acquired factors are the primary drivers.

Autoimmune Diseases

Autoimmune diseases occur when the body's immune system mistakenly attacks its own healthy tissues. While there is often a genetic *susceptibility* or predisposition to developing an autoimmune condition, the disease itself is not directly inherited in a Mendelian fashion. Environmental triggers are usually thought to play a significant role in initiating the autoimmune response in genetically susceptible individuals.

Examples include:

Rheumatoid Arthritis: While genetic factors influence susceptibility, viral infections and environmental exposures are implicated in its development.
Systemic Lupus Erythematosus (Lupus): Similar to RA, genetics play a role in susceptibility, but environmental triggers like sunlight, infections, and certain medications are often cited.
Multiple Sclerosis (MS): Certain genes increase the risk, but it's widely believed that viral infections and geographical factors (like Vitamin D levels) are critical in its onset.
Type 1 Diabetes: As mentioned earlier, this is an autoimmune destruction of insulin-producing cells, with genetic susceptibility but likely triggered by environmental factors.
Graves' Disease: An autoimmune disorder affecting the thyroid gland, with genetic links but influenced by external factors.

The complexity here is that you might inherit a "tendency" for your immune system to go awry, but the specific autoimmune disease you develop, and when you develop it, is often heavily influenced by acquired triggers. It's not a simple gene-to-disease inheritance.

Neurological Disorders (Many Forms)

While conditions like Huntington's disease and early-onset Alzheimer's have clear hereditary patterns, many other neurological disorders are acquired.

Examples include:

Alzheimer's Disease (Late-onset): While there are genetic risk factors (like APOE ε4), most late-onset Alzheimer's cases are not directly inherited. Lifestyle, cardiovascular health, and potentially environmental factors are significant contributors.
Parkinson's Disease: While a small percentage of Parkinson's cases are hereditary, the majority are sporadic, meaning they develop due to a combination of aging, environmental toxins, and other unknown factors.
Stroke: As discussed under cardiovascular diseases, stroke is often a result of acquired risk factors.
Epilepsy: While some forms of epilepsy are genetic, many are acquired, resulting from brain injury (trauma, stroke), infections (meningitis), or tumors.
Amyotrophic Lateral Sclerosis (ALS) / Lou Gehrig's Disease: Most cases of ALS are sporadic, meaning they are not inherited. A small percentage (5-10%) are familial.

My own experience with researching Alzheimer's for my family made me acutely aware that while genetics play a role in some forms, the dominant narrative for many individuals involves acquired factors like vascular health and lifestyle. This offers a glimmer of hope for intervention.

Mental Health Conditions (Complex, but many are acquired)

Mental health is another area where the interplay of genetics and environment is crucial, and many conditions are not strictly hereditary.

Examples:

Depression and Anxiety Disorders: While there can be a genetic predisposition, major life stressors (trauma, loss, chronic stress), environmental factors, and learned behaviors are significant triggers and contributors.
Post-Traumatic Stress Disorder (PTSD): Directly caused by experiencing or witnessing a traumatic event. It is an acquired condition stemming from a specific experience.
Substance Use Disorders: While genetic factors can influence susceptibility to addiction, the development of these disorders is heavily driven by environmental factors, social influences, and personal choices.
Adjustment Disorders: Reactions to identifiable stressors, such as a job loss or divorce.

It's crucial to avoid stigmatizing mental health issues. While genetics can contribute to vulnerability, the majority of diagnoses are triggered or exacerbated by life experiences and environmental circumstances.

Factors Contributing to Non-Hereditary Diseases

Understanding *why* these diseases develop, even without a genetic inheritance, is key to prevention and management. The contributing factors are multifaceted and often interconnected.

Environmental Exposures

The world we live in exposes us to a vast array of substances and conditions that can impact our health. Some are unavoidable, while others are linked to our choices or geographical location.

Pollution: Air pollution (particulate matter, ozone) is linked to respiratory illnesses, cardiovascular disease, and even neurological issues. Water pollution can lead to various infections and toxic exposures.
Toxins: Exposure to heavy metals (lead, mercury), pesticides, industrial chemicals, and endocrine disruptors can have long-term health consequences, including developmental problems, neurological damage, and increased cancer risk.
Radiation: Exposure to ionizing radiation (e.g., from medical imaging, industrial sources, or natural sources like radon) can damage DNA and increase cancer risk.
Occupational Hazards: Certain professions expose individuals to specific risks, such as asbestos exposure leading to mesothelioma, or silica dust causing silicosis.

Lifestyle Choices

These are arguably the most impactful and, importantly, modifiable factors for a large number of non-hereditary diseases.

Diet:

A diet high in processed foods, sugar, unhealthy fats, and sodium contributes to obesity, heart disease, diabetes, and certain cancers.
Conversely, a diet rich in fruits, vegetables, whole grains, and lean proteins can be protective against many chronic diseases.

Physical Activity:

Lack of regular exercise is a major risk factor for obesity, heart disease, type 2 diabetes, and osteoporosis.
Regular physical activity strengthens the heart, improves circulation, helps maintain a healthy weight, and boosts mood.

Smoking and Alcohol Consumption:

Smoking is a leading cause of lung cancer, heart disease, stroke, and numerous other cancers.
Excessive alcohol consumption is linked to liver disease, pancreatitis, certain cancers, and cardiovascular problems.

Stress Management:

Chronic stress can have profound effects on the body, contributing to high blood pressure, weakened immune function, digestive problems, and mental health issues.
Effective stress management techniques (mindfulness, exercise, seeking support) are crucial for overall health.

Sleep:

Chronic sleep deprivation can disrupt hormone balance, impair cognitive function, weaken the immune system, and increase the risk of obesity and cardiovascular disease.

Infections

As mentioned earlier, infectious agents are direct causes of many non-hereditary diseases. The spread and impact of these infections depend on factors like hygiene, vaccination rates, sanitation, and the individual's immune status.

Accidents and Trauma

The likelihood of experiencing accidents can be influenced by environmental factors (e.g., road conditions, workplace safety), personal behavior (e.g., distracted driving, not wearing safety equipment), and even individual traits like reaction time, but the event itself is external and not inherited.

Understanding Risk vs. Determinism

It's crucial to reiterate the distinction between a genetic predisposition and a deterministic inheritance. Having a gene variant that increases your risk for a certain condition does *not* mean you will inevitably develop it. Similarly, not having a strong family history of a disease does *not* grant immunity.

Consider the example of heart disease. A person might have a family history of early heart attacks, indicating a potential genetic susceptibility. However, if they maintain a healthy lifestyle—eating well, exercising regularly, not smoking, managing stress—they can significantly mitigate that inherited risk. Conversely, someone with no family history who adopts an unhealthy lifestyle (poor diet, sedentary, smoking) may still develop heart disease.

This highlights the empowering aspect of understanding non-hereditary diseases. While we cannot change our genes, we have substantial control over our lifestyle and environment. Focusing on modifiable risk factors is paramount for preventing the majority of diseases that afflict humanity.

A Personal Perspective on Risk Mitigation

Looking back, my initial fear after learning about my grandmother's Alzheimer's was palpable. I worried that my fate was sealed. However, as I delved deeper into the research, I realized that while genetics play a role in *some* forms of Alzheimer's, late-onset Alzheimer's, the most common type, is far more complex. The understanding that lifestyle factors—cardiovascular health, diet, cognitive engagement, sleep—can influence risk was incredibly liberating. It shifted my focus from a passive acceptance of genetic destiny to an active pursuit of health-promoting behaviors. This is the power of understanding which diseases are *not* hereditary; it places agency back into our hands.

Preventing Non-Hereditary Diseases: A Proactive Approach

Since a vast number of diseases are acquired, the most effective approach to health is often preventative. This involves making conscious choices that reduce exposure to risk factors and promote overall well-being.

Key Strategies for Prevention

Maintain a Healthy Weight: This is fundamental for preventing type 2 diabetes, heart disease, and certain cancers.
Eat a Balanced Diet: Focus on whole foods, fruits, vegetables, lean proteins, and healthy fats. Limit processed foods, sugary drinks, and excessive salt.
Engage in Regular Physical Activity: Aim for at least 150 minutes of moderate-intensity aerobic activity or 75 minutes of vigorous-intensity activity per week, plus muscle-strengthening activities.
Avoid Smoking and Limit Alcohol: These are two of the most significant modifiable risk factors for many diseases.
Practice Good Hygiene: Frequent handwashing is crucial for preventing the spread of infectious diseases.
Get Vaccinated: Vaccinations protect against many serious infectious diseases.
Manage Stress Effectively: Develop healthy coping mechanisms for stress.
Prioritize Sleep: Aim for 7-9 hours of quality sleep per night.
Protect Yourself from Environmental Hazards: Use sunscreen, avoid prolonged sun exposure, be mindful of air quality, and take precautions in potentially toxic environments.
Regular Medical Check-ups: Early detection of conditions like high blood pressure, high cholesterol, and pre-diabetes allows for timely intervention.

Creating a Healthy Environment

Beyond personal choices, advocating for and creating healthier communities also plays a role. This includes:

Supporting policies that reduce pollution.
Promoting access to healthy foods.
Ensuring safe workplaces and public spaces.
Improving access to healthcare and preventative services.

The Nuance of Gene-Environment Interaction

It's important to acknowledge that the dichotomy between hereditary and acquired isn't always black and white. Gene-environment interaction is a critical concept in modern medicine. This refers to how an individual's genetic makeup can influence their response to environmental factors, and vice versa.

For example:

Someone with a genetic predisposition to lung cancer will have a dramatically increased risk if they smoke compared to someone without that predisposition who also smokes. The gene amplifies the environmental risk.
Conversely, someone with a genetic predisposition to Type 2 diabetes might never develop it if they consistently maintain a healthy diet and exercise regimen. The environment counteracts the genetic risk.

Understanding these interactions allows for more personalized risk assessment and tailored prevention strategies. However, even with these interactions, the fundamental cause of the disease manifestation often involves an acquired trigger or the lack of a protective environment.

Frequently Asked Questions (FAQs) About Non-Hereditary Diseases

Q1: If a disease isn't hereditary, does that mean it's entirely my fault if I get it?

A1: This is a very sensitive and important question. It's crucial to avoid placing blame. While lifestyle choices and environmental exposures are significant drivers of many non-hereditary diseases, attributing them solely to personal fault oversimplifies a complex reality. Many factors influence our ability to make healthy choices. Socioeconomic status, access to healthy food and safe places to exercise, education levels, the presence of chronic stress, cultural norms, and even our mental health can all impact our behaviors. Furthermore, some acquired conditions, like accidental injuries or infections, are simply unfortunate events. The goal of understanding non-hereditary diseases should be empowerment and prevention, not judgment. It’s about recognizing where we *can* exert control and seeking support when circumstances make healthy choices difficult.

Q2: How can I tell if a disease in my family is hereditary or acquired?

A2: Determining whether a disease is hereditary or acquired involves careful observation and, often, consultation with healthcare professionals. Here are some key indicators:

Pattern of Inheritance: Does the disease seem to appear in every generation? Are there specific relatives (parents, siblings, grandparents) who have it? A clear pattern across multiple generations, particularly if it follows a dominant or recessive inheritance, suggests a hereditary component.
Age of Onset: Hereditary conditions often manifest at a younger age than their acquired counterparts. For instance, early-onset Alzheimer's disease is often hereditary, while late-onset Alzheimer's is more complex and influenced by acquired factors.
Specific Diagnoses: Some diseases are almost exclusively hereditary (e.g., Cystic Fibrosis, Huntington's Disease), while others are almost exclusively acquired (e.g., Common Cold, injuries). Many, like heart disease, diabetes, and certain cancers, have both hereditary and acquired forms or influences.
Environmental and Lifestyle Factors: Does the condition strongly correlate with specific exposures or lifestyle habits within the family? For example, if several family members have lung cancer and are all heavy smokers, smoking is likely the primary driver, even if there's a general genetic susceptibility to cancer.
Genetic Testing: For certain conditions, genetic testing can definitively identify inherited gene mutations associated with specific diseases. This is often recommended if there's a strong family history.

It’s always best to discuss your family health history with your doctor. They can help you differentiate between the influences and advise on appropriate screening or preventive measures.

Q3: Are there any diseases that have absolutely no genetic component whatsoever?

A3: This is a philosophical and scientific question that can be difficult to answer with absolute certainty in every single case. In the strictest sense, virtually every biological process in the human body is influenced by genes at some level. However, when we talk about a disease being "hereditary," we typically mean that the primary cause is a mutation in genes passed from parents to offspring, which directly leads to the disease. In contrast, "acquired" diseases develop due to external factors or internal processes *independent* of inherited genetic defects.

So, while a pure "no genetic component whatsoever" is hard to prove for every disease, we can confidently categorize diseases as **primarily acquired** when their development is overwhelmingly driven by non-hereditary factors like infections, injuries, lifestyle choices, and environmental exposures. For example, a common cold is caused by a virus you contract; your genes don't cause the rhinovirus infection. A broken bone is caused by trauma, not an inherited bone defect (though bone density can have a genetic influence, the fracture itself is acquired). These are the diseases that fit the spirit of the question – conditions that you don't pass down through your DNA.

Q4: How can I start making changes to prevent diseases that aren't hereditary if I feel overwhelmed?

A4: Feeling overwhelmed is completely normal, especially when considering the breadth of factors influencing health. The key is to start small and build momentum. Here’s a practical approach:

Identify One Area: Don't try to overhaul everything at once. Pick one aspect of your lifestyle that you feel you can realistically change. Is it drinking more water? Adding a short walk to your day? Eating one extra serving of vegetables?
Set Achievable Goals: Instead of aiming for "lose 50 pounds," aim for "walk for 15 minutes, three times this week." Small, consistent wins build confidence and lead to larger changes over time.
Focus on Addition, Not Just Subtraction: Instead of just thinking about what to cut out (e.g., "no more soda"), focus on what to add (e.g., "add one glass of water with every meal"). This can feel less restrictive and more positive.
Find Support: Talk to friends, family, or a doctor about your goals. Joining a walking group, a healthy cooking class, or seeking advice from a registered dietitian can provide accountability and guidance.
Be Patient and Kind to Yourself: There will be setbacks. Missed workouts or unhealthy meals are not failures; they are part of the journey. Acknowledge them, learn from them, and get back on track without dwelling on them. Consistency over perfection is the mantra.
Educate Yourself (in manageable doses): Understanding *why* certain changes are beneficial can be motivating. Read articles or listen to podcasts about topics that interest you, but avoid information overload.

The goal is to build sustainable habits that contribute to long-term health, rather than quick fixes. Even minor improvements can have a significant positive impact over time.

Conclusion: Empowering Health Through Understanding

The question, "Which disease is not hereditary," opens a door to understanding the vast landscape of acquired conditions that shape our health. While our genetic inheritance plays a role, it is far from the sole determinant of our well-being. Infectious diseases, injuries, and a multitude of chronic illnesses—including many forms of heart disease, type 2 diabetes, cancer, and autoimmune disorders—are primarily driven by factors we can influence: our lifestyle choices and our environment.

Recognizing that a disease is *not* hereditary is not about assigning blame; it is about recognizing agency. It’s about understanding that proactive measures, informed by knowledge, can empower us to significantly reduce our risk and improve our quality of life. By focusing on a balanced diet, regular physical activity, avoiding harmful substances, managing stress, and staying informed through regular medical check-ups, we can actively navigate our health journey and build a stronger, more resilient future, independent of any predetermined genetic fate.

Which Disease Is Not Hereditary? Understanding Acquired Conditions