73Sequencing DNA in subset of patients most likely to carry causative mutations leads
to identifi cation of more actual mutations. This refi ned technique may identify indi-
viduals more likely to have mutations in causal genes. By applying their methods to
real DNA samples from patients with genetic hearing loss, the researchers’ approach
helped them to select from GWAS data a subset of cases for sequencing analysis
that were most likely to carry causative mutations. Sequencing the DNA in this
subset, the study team found that the majority of those patients carried an actual
mutation known to cause hearing loss. This approach will facilitate personalized
medicine, in which treatment will be tailored to an individual’s genetic profi le.
Identifying causal variants in disease genes provides an opportunity to develop
drugs to rectify the biological consequences of these mutated genes.
Application of Proteomics in Molecular Diagnosis
Discovery of the genetic sequence encoding a protein by nucleic acid technologies
is not suffi cient to predict the size or biological nature of a protein. Studies at the
messenger RNA (mRNA) level can assess the expression profi les of transcripts but
these analyses measure only the relative amount of an mRNA encoding a protein
and not the actual amount of protein in a tissue. To address this area, several protein-
based analysis technologies have been developed.
Proteomics investigations endeavor to provide a global understanding of gene
product synthesis rate, degradation rate, functional competence, posttranslational
modifi cation, subcellular distribution and physical interactions with other cell com-
ponents. Usual sequence of events in proteomics is as follows: samples → protein
separation → gel analysis → differential protein expression → sequence analysis.
Bioinformatic systems integrate clinical data, robotics and protein identifi cation
into an automated process.
There is no protein analog of PCR and most of the work in the past has been
manual. 2D GE has been the key technology for protein expression and mass spec-
trometry is the method of choice for connecting the genome and proteome worlds.
Proteomic technologies are considered to be a distinct group within molecular
diagnostics and should not be confused with immunoassays although some pro-
teomic technologies are antibody-based. Proteomics will facilitate mass screening
at the protein level to supplement the genetic screening and fi ll a gap in molecular
medicine. Proteomic data can provide clinical biomarkers for monitoring patient
progress (see Chap. 3 ).
Proteomic Technologies
Technologies with the greatest potential are 2D PAGE, antibody-based screening,
protein-binding assays and protein biochips. Protein biochips were described earlier
in this chapter. 2D PAGE is combined with mass spectroscopy-based sequencing
Application of Proteomics in Molecular Diagnosis