Causes of Non-infectious Disease — Overview

Q1 — Sample Band 6 response (8 marks), annotated

Classification and mechanism:

Type 2 diabetes is classified primarily as a nutritional non-infectious disease, but is best understood as multifactorial. Excess dietary refined carbohydrates and saturated fats, combined with physical inactivity, leads to obesity and sustained hyperinsulinaemia; over time, target cells (liver, muscle, adipose) become resistant to insulin signalling (insulin resistance). However, genetic predisposition is also essential: Indigenous Australians and South Asian populations have 3–4× higher baseline risk, reflecting genetic variants in insulin secretion and signalling pathways. Neither dietary excess nor genetic susceptibility alone is sufficient in most cases. [1 — correct category + mechanism]

Lung cancer is classified as cancer with a primary environmental cause. Tobacco smoke carcinogens (polycyclic aromatic hydrocarbons, nitrosamines) cause covalent DNA adducts in bronchial epithelial cells, inducing mutations in tumour suppressor genes (e.g. TP53) and proto-oncogenes (e.g. KRAS). Accumulated mutations disrupt cell cycle control, producing uncontrolled proliferation. [1 — correct category + mechanism]

Melanoma is classified as cancer with a primary environmental cause. Ultraviolet (UV) radiation induces thymine dimer formation in melanocyte DNA, causing mutations in tumour suppressor genes (e.g. CDKN2A encoding p16) and in BRAF. These mutations remove cell cycle checkpoints, leading to uncontrolled melanocyte division. [1 — correct category + mechanism]

Cystic fibrosis is classified as a genetic non-infectious disease. A mutation in both copies of the CFTR gene (most commonly the F508del mutation) produces a misfolded chloride ion channel protein that is degraded before reaching the cell membrane. Without functional CFTR, chloride and water cannot be secreted into airways, producing abnormally thick dehydrated mucus that obstructs the lungs and digestive tract. There are no modifiable risk factors — CF is determined entirely by inherited genotype. [1 — correct category + mechanism]

CF vs T2D — pure genetic vs multifactorial: Cystic fibrosis is a purely genetic disease: it requires mutations in both CFTR alleles (autosomal recessive) and no lifestyle or environmental exposure can cause or prevent it, only modify its severity. Prevalence (approximately 1 per 2,500 live births) reflects the carrier frequency of the mutation in the population. Type 2 diabetes, by contrast, is multifactorial: genetic susceptibility sets the baseline probability, but the disease is triggered by nutritional and environmental exposures (obesity, inactivity, high-sugar diet). Removing the environmental/nutritional triggers dramatically reduces incidence even in genetically susceptible individuals — which is why lifestyle intervention is the primary prevention strategy. This contrast illustrates the difference between diseases where genetics determines outcome (CF) and diseases where genetics modulates, but does not determine, outcome (T2D). [1 — CF vs T2D contrast with multifactorial concept]

Modifiable and non-modifiable risk factors in multifactorial diseases: For Type 2 diabetes, melanoma, and lung cancer, the data show both modifiable risk factors (diet, UV exposure, smoking — all alterable by individual or population-level intervention) and non-modifiable risk factors (ethnicity, fair skin genotype, genetic carcinogen susceptibility — not changeable through behaviour). This pattern is consistent with multifactorial disease: the disease probability is set by the non-modifiable genetic background but can be substantially raised or lowered by modifying the modifiable factors. A person with CDKN2A mutation (non-modifiable) who consistently uses SPF50+ sunscreen and avoids solaria (modifying the UV exposure risk factor) has far lower melanoma risk than one who does not — the genetic predisposition remains, but its expression is modified. [1 — modifiable/non-modifiable distinction with example]

Prevention effectiveness by category: The data suggest that diseases with a high proportion of modifiable risk factors are most amenable to population-level prevention. Lung cancer (~85% of cases attributable to smoking) has been significantly reduced in Australia through tobacco taxation, advertising bans, and plain packaging legislation. Melanoma rates in young Australians have declined following the ‘Slip-Slop-Slap’ campaign and skin cancer screening. Type 2 diabetes, while preventable through lifestyle modification, is harder to prevent at scale because the modifiable risk factors (diet, physical activity) are themselves shaped by socioeconomic and environmental determinants outside individual control. Cystic fibrosis, as a purely genetic disease, cannot be prevented through lifestyle intervention; population-level prevention relies on newborn screening and genetic counselling. [1 — prevention effectiveness analysis]

Evidence-based judgement: The data indicate that environmental non-infectious diseases (particularly those with a single dominant modifiable risk factor such as tobacco smoke for lung cancer or UV for melanoma) are most amenable to population-level prevention, because targeting the primary environmental exposure reduces incidence across an entire population. Purely genetic diseases like cystic fibrosis cannot be prevented by modifying exposure but can be managed through pharmacological intervention (e.g. CFTR modulators like ivacaftor). Multifactorial diseases (Type 2 diabetes, cardiovascular disease) present the greatest prevention challenge because they require intervention across multiple interacting domains simultaneously. [1 — explicit evidence-based judgement]

Marking criteria (8 marks):

• 1 mark each × 4 — Correct category + mechanistic justification for each of the four conditions (CF, T2D, lung cancer, melanoma).
• 1 mark — Explicitly contrasts CF (purely genetic; non-modifiable) with T2D (multifactorial; genetic predisposition + environmental/nutritional triggers) and links this to the concept of multifactorial disease.
• 1 mark — Explains why having both modifiable and non-modifiable risk factors is characteristic of multifactorial disease and uses at least one named example to illustrate how modifiable risk factors can be targeted while non-modifiable factors remain.
• 1 mark — Reaches an explicit, evidence-grounded judgement about which disease category is most amenable to prevention, with reasoning from the data (e.g. environmental diseases with single dominant modifiable cause vs multifactorial diseases with multiple interacting factors).

Q2 — Sample Band 6 response (7 marks), annotated

The claim is largely flawed, though it contains one defensible element. [1 — overall judgement]

Defensible element: Lifestyle factors — diet, physical activity, smoking — are genuine modifiable risk factors for several major non-infectious diseases including Type 2 diabetes, cardiovascular disease, and lung cancer. Lifestyle modification is a legitimate and evidence-based prevention strategy for these conditions. The lesson’s Card 4 and AIHW data both confirm this. [1 — concedes the defensible element]

Flaw 1 — “personal responsibility eliminates the burden”: The claim treats non-infectious disease purely as a product of individual choice, ignoring the socioeconomic determinants of health. Access to healthy food, safe exercise environments, and preventive healthcare is unequally distributed across Australian society. Indigenous Australians experience cardiovascular disease at 1.7× and diabetes at 3× the national average — these disparities reflect genetic, historical, environmental, and socioeconomic inequalities, not simply individual choices. The “personal responsibility” framing ignores structural determinants entirely. [1 — refutes personal responsibility claim with data]

Flaw 2 — “genetic risk is minor and easily overridden”: This is incorrect for purely genetic diseases (cystic fibrosis, Huntington’s disease, Type 1 diabetes) where no lifestyle modification can prevent or cause the disease. Even for multifactorial diseases, genetic predisposition cannot be “overridden” — it can only be partially mitigated. A person with a BRCA1 mutation has significantly elevated breast cancer risk regardless of lifestyle choices; the mutation cannot be eliminated by diet or exercise. [1 — refutes “genetics is minor”]

Flaw 3 — “dominance of NID means people live less healthily today than in 1950”: This fundamentally misreads the epidemiological transition. Non-infectious diseases dominate today’s mortality statistics not because Australians are less healthy, but because public health measures (vaccines, antibiotics, sanitation, improved nutrition) successfully reduced premature death from infectious diseases. Australians in 1950 did not “live healthier lives” — they died in much larger numbers from infectious diseases before reaching the age at which non-infectious diseases typically manifest. The dominance of NID is partly a success story of public health, not a failure of individual behaviour. [1 — corrects epidemiological transition misreading]

Flaw 4 — burden would be “eliminated”: Even perfect lifestyle modification across the entire population would not eliminate NID. Cystic fibrosis, Huntington’s disease, Down syndrome, and other genetic conditions are entirely unaffected by lifestyle. Some cancers arise from spontaneous somatic mutations with no identifiable environmental trigger. The claim dramatically overstates what lifestyle intervention can achieve. [1 — refutes “eliminated”]

Defensible reformulation: “Modifiable lifestyle factors — including diet, physical activity, and tobacco use — are among the most important and actionable risk factors for several major non-infectious diseases, including Type 2 diabetes, cardiovascular disease, and lung cancer. Population-level reductions in these modifiable risk factors could substantially lower the burden of these conditions. However, the full burden of non-infectious disease cannot be eliminated through lifestyle modification alone: purely genetic diseases are unaffected; genetic predisposition in multifactorial diseases cannot be changed; socioeconomic determinants of health shape access to healthy behaviours; and the epidemiological dominance of NID reflects the success of infectious disease control rather than a decline in population health behaviours.” [1 — defensible reformulation with all elements]

Marking criteria (7 marks):

• 1 mark — States an overall evaluative judgement (e.g. “largely flawed but contains one defensible element”).
• 1 mark — Correctly identifies the defensible element: lifestyle factors are genuine modifiable risk factors for several non-infectious diseases, and lifestyle modification is a legitimate evidence-based prevention strategy.
• 1 mark — Refutes “personal responsibility eliminates the burden” with reference to socioeconomic/structural determinants of health and/or AIHW data on health disparities (e.g. Indigenous Australians).
• 1 mark — Refutes “genetic risk is minor and easily overridden” with reference to purely genetic diseases (CF, Huntington’s, T1D) or the non-modifiable nature of genetic predisposition in multifactorial diseases.
• 1 mark — Correctly explains that the epidemiological dominance of NID reflects the success of infectious disease control (epidemiological transition) rather than a decline in lifestyle quality, citing at least one relevant mechanism (vaccines, antibiotics, sanitation).
• 1 mark — Refutes “eliminated” with a specific example of a non-infectious disease that cannot be prevented through lifestyle modification (e.g. cystic fibrosis, Huntington’s, random somatic cancers).
• 1 mark — Provides a biologically defensible reformulation that acknowledges the role of lifestyle as a modifiable risk factor while correctly embedding it within the multifactorial, socioeconomic, and genetic context of non-infectious disease causation.