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the elucidation of diseases that are multifactorial and involve a significant contribu-

tion from environmental factors. One of the best-studied examples of this type of

disease is cancer. Molecular genetic analysis has allowed a discrete set of cellular

genes, termedoncogenes, to be defined which play key roles in such events. These

genes and their proteins are also major points in the cell cycle and are intimately

invloved in cell regulation. A number of these are indicated in Table 6.8. In a number

of cancers well-defined molecular events have been correlated with mutations in these

oncogenes and therefore in the corresponding protein. It is already possible to screen

and predict the fate of some disease processes at an early stage, a point which itself

raises significant ethical dilemmas. In addition to understanding cellular processes

both in normal and disease states great promise is also held in drug discovery and

molecular gene therapy. A number of genetically engineered therapeutic proteins and

enzymes have been developed and are already having an impact on disease manage-

ment. In addition the correction of disorders at the gene level (gene therapy) is also

under way and perhaps is one of the most startling applications of molecular biology

to date. A number of these developments are indicated in Table 6.9.

Table 6.9A number of selected examples of targets for gene therapy

Disorder Defect Gene target Target cell

Emphysema Deficiency (a1-AT) a1-Antitrypsin (a1-AT) Liver cells

Gaucher disease
(storage disorder)

GC deficiency Glucocerebrosidase GC fibroblasts

Haemoglobinopathies Thalassaemia b-Globin Fibroblasts

Lesch–Nyhan syndrome Metabolic deficiency Hypoxanthine guanine
phosphoribosyl
transferase (HPRT)

HPRT cells

Immune system
disorder

Adenosine deaminase

deficiency

Adenosine deaminase

(ADA)

T and B cells

Table 6.10Current selected plant/crops modified by genetic

manipulation

Crop or plant Genetic modification

Canola (oil seed rape) Insect resistance, seed oil modification

Maize Herbicide tolerance, resistance to insects

Rice Modified seed storage protein, insect resistance

Soya bean Tolerance to herbicide, modified seed storage protein

Tomato Modified ripening, resistance to insects and viruses

Sunflower Modified seed storage protein

261 6.11 Molecular biotechnology and applications