Investigate the causes and effects of non-infectious diseases in humans, including but not limited to: genetic diseases, diseases caused by environmental exposure, nutritional diseases and diseases caused by cancer

What this dot point is asking

NESA wants you to classify non-infectious diseases by cause and to provide named examples with mechanisms. The distinction from infectious disease (covered in Module 7) is the absence of a transmitted pathogen.

The answer

A non-infectious disease is a disease that is not caused by a pathogen and is not transmitted between hosts. The main causal categories are genetic, environmental, nutritional, lifestyle and age-related (degenerative). Cancer cuts across several categories and is often treated as its own group.

Genetic diseases

Caused by mutations in DNA. The mutation may be inherited from parents or arise de novo in a gamete or early embryo.

Mechanisms.

• Single-gene (Mendelian) disorders. One gene, one disease. Example: cystic fibrosis (autosomal recessive, CFTR gene), Huntington's disease (autosomal dominant, HTT gene), haemophilia A (X-linked recessive, F8 gene).
• Chromosomal disorders. Whole-chromosome abnormalities. Example: Down syndrome (trisomy 21), Turner syndrome (45,X).
• Polygenic and multifactorial. Many genes plus environment. Example: type 2 diabetes, schizophrenia, most cancers.

Environmental diseases

Caused by exposure to physical, chemical or biological agents.

Mechanisms.

• Chemical. Asbestos fibres cause mesothelioma; benzene exposure causes leukaemia; lead exposure causes neurological damage.
• Physical. UV radiation causes skin cancer (melanoma, basal and squamous cell carcinoma); ionising radiation causes various cancers and acute radiation syndrome.
• Air pollution. Particulate matter (PM2.5) causes chronic obstructive pulmonary disease (COPD) and ischaemic heart disease.
• Biological toxins. Aflatoxin from Aspergillus fungi on stored grain causes liver cancer.

Nutritional diseases

Caused by deficiency or excess of nutrients.

Deficiency examples.

• Scurvy. Vitamin C deficiency. Impaired hydroxylation of proline in collagen leads to bleeding gums, poor wound healing.
• Rickets. Vitamin D or calcium deficiency in children. Soft, deformed bones.
• Iron-deficiency anaemia. Low haemoglobin synthesis, fatigue, pallor.
• Kwashiorkor. Severe protein deficiency. Oedema, hepatomegaly, growth failure.

Excess examples.

• Type 2 diabetes. Chronic excess of refined carbohydrates and obesity drive insulin resistance.
• Cardiovascular disease. Excess saturated fats and salt contribute to atherosclerosis and hypertension.
• Obesity. Energy intake exceeding expenditure.

Lifestyle diseases

Caused by behavioural risk factors, often overlapping with nutritional and environmental categories.

Examples.

• Lung cancer. 80 to 90 percent of cases are caused by tobacco smoking. Tar contains polycyclic aromatic hydrocarbons that damage DNA in bronchial epithelium.
• Alcohol-related liver disease. Chronic alcohol consumption causes fatty liver, hepatitis and cirrhosis.
• Cardiovascular disease. Sedentary behaviour, smoking, poor diet, stress.
• Skin cancer. Sun exposure without protection.

Age-related (degenerative) diseases

Caused by cumulative cellular damage and reduced tissue repair with age.

Examples.

• Alzheimer's disease. Accumulation of amyloid-beta plaques and tau tangles in the brain.
• Osteoporosis. Reduced bone mineral density after menopause or with prolonged inactivity.
• Osteoarthritis. Wear of articular cartilage in load-bearing joints.
• Parkinson's disease. Progressive loss of dopaminergic neurons in the substantia nigra.

Cancer as a cross-cutting category

Cancer is uncontrolled cell division caused by accumulated mutations in genes regulating the cell cycle (oncogenes and tumour suppressor genes such as TP53). It can be:

• Genetic. BRCA1/BRCA2 inherited mutations predispose to breast and ovarian cancer.
• Environmental. UV-induced melanoma, asbestos-induced mesothelioma.
• Lifestyle. Tobacco-induced lung cancer, alcohol-induced oral cancer.
• Infection-associated. Cervical cancer from HPV, liver cancer from hepatitis B (the trigger is infectious, but the cancer itself is not transmitted).

Effects on the individual and society

Individual effects. Pain, disability, reduced life expectancy, psychological impact, loss of income.

Societal effects. Health-care costs (non-infectious disease accounts for over 70 percent of Australia's disease burden), workforce productivity losses, demand for aged care and chronic disease services. Non-infectious disease now causes more deaths globally than infectious disease in every region except sub-Saharan Africa.

Worked example

A 60-year-old woman is diagnosed with type 2 diabetes. Her father had the same condition; she has a BMI of 32 and a sedentary office job.

Causal analysis.

• Genetic predisposition. Family history suggests inherited susceptibility (variants in genes such as TCF7L2).
• Nutritional and lifestyle factors. Excess calorie intake, sedentary behaviour and obesity drive insulin resistance.
• Mechanism. Chronic hyperglycaemia from impaired insulin signalling damages blood vessels, the kidneys, retinas and peripheral nerves.

Classification. Multifactorial non-infectious disease combining genetic and lifestyle factors.

Common traps

Saying "diet causes diabetes" without specifying type. Type 1 is autoimmune and not lifestyle-related. Type 2 is the lifestyle-linked form.

Confusing cause and risk factor. A risk factor (e.g. obesity) increases the probability of disease but does not deterministically cause it. A cause (e.g. CFTR mutation in cystic fibrosis) is necessary.

Forgetting that non-infectious does not mean non-transmissible risk. Some non-infectious cancers have infectious triggers (HPV, hepatitis B); markers want you to recognise the nuance.

Generic answers without named examples. "Genetic disease" scores no marks. "Cystic fibrosis, caused by a CFTR mutation on chromosome 7" scores.

In one sentence

Non-infectious diseases are caused by genetic mutations, environmental exposures, nutritional imbalance, lifestyle factors and age-related degeneration, with cancer cutting across all categories and now accounting for the majority of disease burden in developed countries.