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.

Examples in context

Example 1. Mesothelioma in former Wittenoom asbestos workers. Wittenoom in Western Australia mined crocidolite (blue) asbestos from 1943 to 1966. More than 2000 former workers and residents have since died of malignant mesothelioma, a cancer of the pleural lining caused exclusively by inhaled asbestos fibres. Fibres lodge in lung tissue, where they cannot be cleared by macrophages and slowly induce chronic inflammation and DNA damage in mesothelial cells over 20 to 50 years. The Western Australian Mesothelioma Registry reports incidence of around 6 per 100 000, the highest in the world. Mesothelioma is a textbook environmental non-infectious disease, with a single identifiable causal exposure rather than the polygenic multifactor causation typical of cardiovascular disease or type 2 diabetes.

Example 2. Type 2 diabetes and obesity in remote Aboriginal communities. The Northern Territory has the highest rate of type 2 diabetes in Australia, particularly in remote Aboriginal communities where prevalence reaches 27 percent of adults compared to 5 percent nationally. The causes are nutritional and lifestyle: rapid dietary transition from traditional bush tucker (low GI, high fibre) to processed foods (high refined sugars and saturated fats), combined with reduced physical activity and rising obesity. Underlying genetic predisposition (the "thrifty gene" hypothesis) and intergenerational health inequities compound the effect. NT Health's Mai Wiru community store nutrition strategy aims to reduce sugar consumption, illustrating how this category of disease requires structural rather than purely individual interventions.

Try this

Q1. Classify the following diseases by their primary cause: (a) Huntington's disease, (b) lung cancer in a smoker, (c) scurvy, (d) Alzheimer's disease. [4 marks]

• Cue. (a) Genetic (CAG expansion in HTT). (b) Environmental/lifestyle (tobacco smoke mutagens). (c) Nutritional (vitamin C deficiency). (d) Age-related neurodegeneration, partly genetic (APOE4 risk).

Q2. Australian Institute of Health and Welfare data show coronary heart disease death rates fell from 380 per 100 000 in 1980 to 70 per 100 000 in 2024. Calculate the percentage reduction and identify two non-infectious risk factors targeted to achieve this. [3 marks]

• Cue. Reduction is approximately 81.6 percent. Risk factors: smoking, hypertension, high LDL cholesterol, obesity, physical inactivity.

Q3. A 55-year-old patient with no genetic family history develops melanoma. (a) Identify the most likely environmental cause. (b) Describe the molecular mechanism by which it causes cancer. (c) Suggest two preventive measures relevant to the Australian population. [1+3+2 marks]

• Cue. (a) UV radiation. (b) Thymine dimers in DNA, mutations in BRAF and other oncogenes drive uncontrolled melanocyte division. (c) SunSmart behaviour, regular skin checks, sunscreen, hats and protective clothing.