362

26

Medicine and Disease

“target recognition” because it allows Cas to recognize and target a specific sequence

of DNA. Once Cas has cut the target DNA it is then able to integrate a new piece of

DNA into the genome (“gene editing”). Hence, specific genes within the genome can

be edited. CRISPR-Cas can in principle be used for human gene therapy to correct

genetic disorders; the faulty gene causing the disorder in a patient is excised and

replaced with a normal gene. In the cells whose DNA has been thus edited, the now

normally functioning gene should produce the proteins that were previously absent

or defective. CRISPR-Cas can also be used to modify existing genes. Yet another

technique applicable to personalized medicine is the therapeutic use of differentiated

embryonic stem cells (cf. Sect. 14.9.1). ²⁵

26.4

Toward Automated Diagnosis

Knowledge of protein expression patterns greatly expands the knowledge of disease

at the molecular level. The full power of the pattern recognition techniques discussed

earlier (Sect. 13.1) can be brought to bear in order to elucidate the hidden mechanisms

of physiological disorder. The technology of large-scale gene expression allows one

to correlate gene expression patterns with disease symptoms. Microarray technol-

ogy has the potential for enabling swift and comprehensive monitoring of the gene

expression profile of a patient. Where correlations become well established through

the accumulation of vast amounts of data, the expression profile becomes useful

for diagnosis, and even for preventive treatment of a condition enhancing suscep-

tibility to infection or allergy. One does not simply seek to correlate the bald list

of expressed proteins and their abundances with disease symptoms, however: the

subtleties of network structure and gene circuit topology are likely to prove more

revealing as possible “causes.”

The differential expression of genes in healthy and diseased tissue is usually

highly revealing. For the purposes of diagnosis, each gene is characterized as a

point in two-dimensional space, the two coördinates corresponding to the relative

abundance of the gene product in the healthy and diseased tissues. This allows a

rapid visual appraisal of expression differences.

The composition of blood is also a highly revealing diagnostic source (cf.

Sect. 23.12). As well as intact peptides and other biomacromolecules, fragments

of larger molecules may also be present. For their identification, mass spectrometry

seems to be more immediately applicable than microarrays.

Gene chips also allow the clear and unambigous identification of foreign DNA in a

patient due to an invading microörganism, obviating the laborious work of attempting

to grow the organism in culture and then identify it phenotypically.

In the future, implantable sensors are expected to be able to offer continuous

monitoring of a large number of relevant physiological parameters and biomarkers

25 Murry and Keller (2008).